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Coordinate Systems All FME features know about their coordinate system and, therefore, their location on the earth. An FME coordinate system contains a complete mathematical model of the conversion between a specific location on the earth and a set of coordinates. Coordinate system definitions are spec- ified by a set of parameters that define this mathematical model, including the earth model (ellipsoid or datum), the units used to measure the coordinates, the projection type, and any parameters specific to the projection type. Coordinate systems may be extracted from input feature data sources, may come predefined with the FME, or may be defined by FME users. The FME allows output coordinate systems that are different than the input ones to be specified and performs the required coordinate con- versions when necessary. FME is shipped with over 5000 coordinate systems based on a variety of different projections, ellipsoids, and datums. The file coordsys.db in the FME installation directory contains the names and descriptions of all predefined coordinate systems. However, some users may wish to use coordinate systems that do not ship with FME, and will need to read the topics on defining custom coordinate systems. When an FME reader knows its coordinate system, the FME creates a coordinate system to match the input data specification and tags each fea- ture read with this system name. However, a majority of formats do not explicitly store the coordinate system. In such cases, mapping file direc- tives are used to supply coordinate system information. The mapping file may also contain a specification as to which coordinate system the output data is to be in. If the output coordinate system is specified and it is different from the input coordinate system, then the FME automatically converts the feature data between coordinate sys- tems. For example, converting features from one coordinate system based on North American Datum (NAD) 27 to another from NAD83 causes the FME to perform the required datum conversion. To ensure that the reprojection is accurate, FME automatically vectorizes arcs, ellipses, rec- tangles, and rounded rectangle objects as necessary before performing the coordinate system change. The output system, or format, stores the coordinate system of the features if it has facilities for doing so; for example, the MapInfo formats store the coordinate system of the data. Quick Links n Changing the Default Coordinate System n Adding a Custom Coordinate System n Sharing Custom Coordinate Systems n Shared Directories n Included Grid Shift Files n Adding Grid Files n Using the CoordinateSystemSetter Transformer Coordinate Systems All FME features know about their coordinate system and, therefore, their location on the earth. An FME coordinate system contains a complete mathematical model of the conversion between a specific location on the earth and a set of coordinates. Coordinate system definitions are spec- ified by a set of parameters that define this mathematical model, including the earth model (ellipsoid or datum), the units used to measure the coordinates, the projection type, and any parameters specific to the projection type. Coordinate systems may be extracted from input feature data sources, may come predefined with the FME, or may be defined by FME users. The FME allows output coordinate systems that are different than the input ones to be specified and performs the required coordinate con- versions when necessary. FME is shipped with over 5000 coordinate systems based on a variety of different projections, ellipsoids, and datums. The file coordsys.db in the FME installation directory contains the names and descriptions of all predefined coordinate systems. However, some users may wish to use coordinate systems that do not ship with FME, and will need to read the topics on defining custom coordinate systems.
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Page 1: FME Coordinate Systems (FME Workbench) - Safe Softwaredocs.safe.com/fme/2013/pdf/FMECoordinateSystems.pdf · COORDINATE_SYSTEM_DEF anystring Thisparameterisusedtospecifythenameofthe

Coordinate Systems

All FME features know about their coordinate system and, therefore, their location on the earth. An FME coordinate system contains a completemathematical model of the conversion between a specific location on the earth and a set of coordinates. Coordinate system definitions are spec-ified by a set of parameters that define this mathematical model, including the earth model (ellipsoid or datum), the units used to measure thecoordinates, the projection type, and any parameters specific to the projection type.

Coordinate systems may be extracted from input feature data sources, may come predefined with the FME, or may be defined by FME users.The FME allows output coordinate systems that are different than the input ones to be specified and performs the required coordinate con-versions when necessary.

FME is shipped with over 5000 coordinate systems based on a variety of different projections, ellipsoids, and datums. The file coordsys.dbin the FME installation directory contains the names and descriptions of all predefined coordinate systems. However, some users may wish touse coordinate systems that do not ship with FME, and will need to read the topics on defining custom coordinate systems.

When an FME reader knows its coordinate system, the FME creates a coordinate system to match the input data specification and tags each fea-ture read with this system name. However, a majority of formats do not explicitly store the coordinate system. In such cases, mapping file direc-tives are used to supply coordinate system information.

The mapping file may also contain a specification as to which coordinate system the output data is to be in. If the output coordinate system isspecified and it is different from the input coordinate system, then the FME automatically converts the feature data between coordinate sys-tems. For example, converting features from one coordinate system based on North American Datum (NAD) 27 to another from NAD83 causesthe FME to perform the required datum conversion. To ensure that the reprojection is accurate, FME automatically vectorizes arcs, ellipses, rec-tangles, and rounded rectangle objects as necessary before performing the coordinate system change. The output system, or format, storesthe coordinate system of the features if it has facilities for doing so; for example, the MapInfo formats store the coordinate system of the data.

Quick Links

n Changing the Default Coordinate System

n Adding a Custom Coordinate System

n Sharing Custom Coordinate Systems

n Shared Directories

n Included Grid Shift Files

n Adding Grid Files

n Using the CoordinateSystemSetter Transformer

Coordinate Systems

All FME features know about their coordinate system and, therefore, their location on the earth. An FME coordinate system contains a completemathematical model of the conversion between a specific location on the earth and a set of coordinates. Coordinate system definitions are spec-ified by a set of parameters that define this mathematical model, including the earth model (ellipsoid or datum), the units used to measure thecoordinates, the projection type, and any parameters specific to the projection type.

Coordinate systems may be extracted from input feature data sources, may come predefined with the FME, or may be defined by FME users.The FME allows output coordinate systems that are different than the input ones to be specified and performs the required coordinate con-versions when necessary.

FME is shipped with over 5000 coordinate systems based on a variety of different projections, ellipsoids, and datums. The file coordsys.dbin the FME installation directory contains the names and descriptions of all predefined coordinate systems. However, some users may wish touse coordinate systems that do not ship with FME, and will need to read the topics on defining custom coordinate systems.

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When an FME reader knows its coordinate system, the FME creates a coordinate system to match the input data specification and tags each fea-ture read with this system name. However, a majority of formats do not explicitly store the coordinate system. In such cases, mapping file direc-tives are used to supply coordinate system information.

The mapping file may also contain a specification as to which coordinate system the output data is to be in. If the output coordinate system isspecified and it is different from the input coordinate system, then the FME automatically converts the feature data between coordinate sys-tems. For example, converting features from one coordinate system based on North American Datum (NAD) 27 to another from NAD83 causesthe FME to perform the required datum conversion. To ensure that the reprojection is accurate, FME automatically vectorizes arcs, ellipses, rec-tangles, and rounded rectangle objects as necessary before performing the coordinate system change. The output system, or format, storesthe coordinate system of the features if it has facilities for doing so; for example, the MapInfo formats store the coordinate system of the data.

Quick Links

n Changing the Default Coordinate System

n Adding a Custom Coordinate System

n Sharing Custom Coordinate Systems

n Shared Directories

n Included Grid Shift Files

n Adding Grid Files

n Using the CoordinateSystemSetter Transformer

How FME Identifies Coordinate Systems

A coordinate system is a reference system for spatial data to be related to a particular space on the Earth's surface. It is made up of a number ofcomponents such as projection (http://en.wikipedia.org/wiki/Map_projection), geoid (http://en.wikipedia.org/wiki/Geoid), datum (http://e-n.wikipedia.org/wiki/Datum) and units (http://en.wikipedia.org/wiki/Units_of_measurement).

Each feature that is processed by FME is coordinate system aware; that is, it knows what coordinate system it belongs to at all times. This helpsprevent confusion when reading multiple datasets that belong to different coordinate systems.

When working with FME, you generally only have to consider the coordinate system if you want to reproject the data to another system or if FMEfails to automatically recognize the correct coordinate system.

Coordinate systems are defined in the Workbench Navigator. Because the source Reader coordinate system is marked <not set>, FME will try todetermine the coordinate system from the source dataset. Because the destination Writer coordinate system is marked <not set>, FME will notreproject the data. Instead FME writes the data using the same coordinate system as the source data.

Each Coordinate System parameter is linked to FME's Coordinate System Gallery. Double-click the parameter to display a list of recently usedcoordinate systems, or the browse button to access FME's Coordinate System Gallery.

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If you define the coordinate systems FME automatically restructures the data at the end of the translation, so that the output is in the correctlocation.

How FME Processes Coordinate Systems in the Workspace

If a coordinate system is specified in both the source format and the workspace, the coordinate system in the workspace is the one that will beused. The coordinate system specified in the source format is not used, and a warning is logged. If a source coordinate system is not specifiedin the workspace and the format or system does not store coordinate system information, then the coordinate system is not set for the featuresthat are read.

If a destination coordinate system is set and the feature has been tagged with a coordinate system, then a coordinate system conversion is per-formed to put the feature into the destination system. This happens after features leave the transformer, but before they enter the trans-formation process.

If the destination coordinate system was not set, then the features are written out in their original coordinate system.

If a destination coordinate system is set, but the source coordinate system was not specified in the workspace or stored in the source format,then no conversion is performed. The features are simply tagged with the output system name before being written to the output dataset.

Choosing from the Coordinate System Gallery

Tools > Browse Coordinate Systems

Browse button beside any Coordinate System field

From the Coordinate System Gallery, you can search for a keyword, filter entries, select a new coordinate system, and view properties onselected coordinate systems.

Any custom coordinate systems that you add will also appear here.

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Changing the Default Coordinate System

By default, FME either uses a default value or uses the coordinate system referenced in the input dataset. However, you may want to convertdata to a different coordinate system.

For formats that know their coordinate system (such as MapInfo and DLG), the Coordinate System field in the Source Dataset dialog will displaySame as source and FME will read the coordinate system from the source dataset. For most other input sources, the field will display <not set>,which means that FME will use default values.

For FME to perform a reprojection, you must specify different writer coordinate system parameters.

Converting to a Different Writer Coordinate System

1. Create a workspace, and define your reader and writer.

2. In the source dataset area in the Navigator pane, the Coordinate System parameter will be displayed as <not set>. This means that FMEwill either use default values, or will read the coordinate system from the source data.

You can explicitly set the source coordinate system (which will override any coordinate system read from the source) but in most cases,you will not need to change the default parameter.

3. In the destination dataset area of the Navigator pane, double-click the Coordinate System parameter.

4. In the dialog that appears, you can either click the Browse button to display the Coordinate System Gallery or enter a prefix or characterstring that will display a list of matching selections. For example, if you type the string "UTM" you will see these matches:

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FME will reproject the data to the coordinate system that you enter in this field, and the Navigator pane will display something similarto this:

Tip: If you add source or destination datasets to a workspace (by choosing Add Reader or Add Writer from the Readers or Writers menus),you can define coordinate systems at the same time.

Grid Shift Files

FME supports conversions between coordinate systems using different datums. See the topics under Coordinate Systems > Datums.

Reprojecting Point Data

Most coordinate conversion tasks are easy to perform with FME. Wherever automated translations are possible, reprojections are as simple aschoosing different reader and writer coordinate systems. The FME features are coordinate system aware and reproject themselves appro-priately.

However, when coordinate data is held in attribute values, this process cannot be completely automated. Tabular data stored in ASCII files can-not be translated automatically. In this case, you must use the AttributeReprojector transformer to accomplish this task.

1. Insert the transformer and connect it to the feature type(s) .

2. Select the X and Y coordinate values.

3. Select the source (reader) and destination (writer) coordinate systems.

This transformer does not alter the feature’s coordinates – only the values of the selected X and Y attributes (if they contain coordinate values)are changed.

Note: Make sure you have not also specified reader and writer coordinate systems through the Navigator pane in Workbench.

Reverting to Detected Coordinate Systems

If you previously changed the source coordinate system, you can revert back to the original, detected coordinate system.

Right-click on the Coordinate System label in the Workbench navigator, and choose Edit Parameter.

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Delete the text in the dialog that appears, and click OK.

The coordinate system label will revert to the original coordinate system (usually <not set>).

Search Envelopes and Coordinate Systems

Using the parameter Search Envelope Coordinate System, you can enter reader search envelope parameters in a different coordinate systemthan the actual data itself; for example you can have data in an Albers coordinate system, but enter a search envelope in Lat/Long.

This function is available in FME 2008+ for any format that has a set of search envelope parameters, which is usually any database plus anumber of other formats.

This screenshot shows where to locate the parameter in the Navigator pane in the Workbench reader parameters. The source data is inLat/Long, but the search envelope has been specified in meters using a UTM coordinate system.

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When you run a workspace with this parameter, FME converts the search envelope into the same coordinate system as the source data, thencreates a bounding box from that, as what started out as an envelope may no longer be rectangular after a reprojection. For this reason the out-put area may be slightly larger than specified.

About Custom Coordinate Systems

A custom coordinate system is a Shared Resource that defines one or more coordinate systems that are not included in FME by default.

FME is used in many different countries around the world, and it is also used with a variety of custom datasets within each country. However,sometimes FME’s Coordinate System Gallery doesn't include the coordinate systems that are being used. In these cases, you will have to definethe coordinate systems before FME can use them.

Related Files

n coordsys.db in the FME installation directory contains the names and descriptions of all predefined coordinate systems. It is typically asubset of all the definitions that are known to FME (that is, there may be some additional systems defined in the coordsys file that aren't inthe coordsys.db either because the systems have been deprecated, or some other reason). Any systems defined in LocalCoordSysDefs.fme,MyCoordSysDefs.fme or as an FME Shared Resource are automatically added to FME and don't need an entry in this file.

n To allow sites to add their own coordinate systems, a file of local coordinate system definitions is automatically loaded and made available toeach FME session. This file is called LocalCoordSysDefs.fme, and resides in the Reproject subdirectory under the FME installationdirectory. It contains a series of COORDINATE_SYSTEM_DEF, DATUM_DEF, ELLIPSOID_DEF, and UNIT_DEF lines that define addi-tional, site-specific coordinate systems. You can edit these files to add your own definitions.

n LocalCoordSysDefs.fme is a file that contains overrides to the standard coordinate systems (and related parameters) defined byFME. The built-in definitions for any coordinate system/datum/ellipsoid may be overridden if by a text defintion in the Repro-ject/LocalCoordSysDefs.fme file. FME ships with a number of overrides (and supplemental) systems in this file. The structure of

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LocalCoordSysDefs.fme is the same as the custom coordinate system file MyCoordSysDefs.fme, and its contents can be used as atemplate for new custom coordinate systems.

You should NOT edit LocalCoordSysDefs.fme, because each time FME is installed, it will overwrite this file with whatever is currentfor that version of FME.

n MyCoordSysDefs.fme in the Reproject directory contains custom coordinate system definitions.

WARNING: Although FME does not overwrite MyCoordSysDefs.fme during installation, it is always good practice to back up the fileanyway. In addition, although you should not have to edit either the LocalCoordSysDefs.fme and coordsys.db files, FME over-writes these files during installation. Therefore, you will have to back up the files if you have made any changes.

Adding a Custom Coordinate System

Use a text editor to edit the MyCoordSysDefs.fme file in your Reproject directory. This directory is located where FME was installed onyour system. (It is always good practice to create a backup copy of the file before you make any changes.)

The projection and units of your source data are not predefined within FME, so, to define them, you must edit the mapping file to add the fol-lowing lines:

Coordinate System Definition Lines Additional Information

COORDINATE_SYSTEM_DEF <coordsysname> \

    PROJ <projType> \ Table of projection types

    UNIT <unitName> \ Table of predefined units

(DT_NAME <datumName> | EL_NAME <ellipName>) \ Table of predefined datums and predefined ellipsoids. Note thateach coordinate system definition must specify either a datum orellipsoid.

[<parameter> <value>]+ \

[DESC_NM <descriptive_name>] \

[GROUP <group_name>] \ Tip: Defining a unique group name allows you to sort coordinatesystems by the "Group" column in the Coordinate System Gallery.

[QUAD <quadrant>] \ Quadrant definition

[SOURCE <source>] \

[ZERO_X <zero_x>] \

[ZERO_Y <zero_y>] \

For example, this mapping file fragment defines a NAD83 based UTM Zone 12 coordinate system.

COORDINATE_SYSTEM_DEF UTM12N83 \

    PROJ TM \

    UNIT METER \

    DT_NAME NAD83 \

    PARM1 -111.0 \

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    GROUP "Custom Group" \

    SCL_RED 0.9996 \

    ORG_LAT 0.0 \

    X_OFF 500000.0 \

   Y_OFF 0.0 \

   MAP_SCL 1.0 \

   ZERO_X 0.001 \

   ZERO_Y 0.001

Edit, save, and close the MyCoordSysDefs.fme file.

Note that you will have to restart Workbench before FME can recognize the custom coordinate system.

The custom coordinate system will appear in the columns of the Coordinate System Gallery. These columns are, in order, Name, Description,Group, Datum, Ellipsoid, Projection, and Units.

When you update to a newer version of FME, the MyCoordSysDefs.fme file will not be overwritten. (However, it is always good prac-tice to back up any custom files.)

Parameter Descriptions

l The parameters above are described in Local Coordinate Systems.l For a complete list of generic parameters that you can define, please see Generic Parameters.

Working with Mapping Files

If you are working with custommapping files and you set coordinate system definitions, you will have to remove the definitions after they aredefined in the MyCoordSysDefs.fme file – the same coordinate system cannot be defined in both places.

See also Sharing Custom Coordinate Systems.

Sharing Custom Coordinate Systems

Coordinate systems can be read from user-defined directories (including network shares).

This option is especially useful for groups who work together. For instance, if an entire workgroup uses just a few custom coordinate systemdefinitions, keeping these definitions in one place means that everyone doesn't have to have a copy. Then, whenever any of the definitions areupdated, the entire group automatically has access to the new version.

See Shared Directories.

Local Coordinate Systems

Name Range Description Optional?

COORDINATE_SYSTEM_DEF any string This parameter is used to specify the name of thecoordinate system being defined may be used toidentify the coordinate system of a reader orwriter, or as an argument to @Reproject or _COORDINATE_SYSTEM.

No

DT_NAME See Datums. This parameter specifies the datum to be used forthe projection. Either a datum or an ellipsoid

Yes

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Name Range Description Optional?

must be specified for each coordinate system.

DESC_NM any string This parameter specifies a descriptive name ofthe definition.

Yes

EL_NAME See Ellipsoids. This parameter specifies the ellipsoid to be usedfor the projection. Either a datum or an ellipsoidmust be specified for each coordinate system.

Yes

GROUP Used to classify coordinate systems into groupsto make selection of a coordinate system from the1,000+ provided a bit easier.

Yes

MAX_LNG This parameter is optional and can be used tospecify the maximum longitude of the usefulrange of the coordinate system. The value isgiven in degrees relative to Greenwich. Positivevalues indicate east longitude, while negativevalues indicate west longitude. Its value shouldbe normalized between -360 and +360 and,when used, must be algebraically greater thanthe MIN_LNG parameter.

Yes

MIN_LNG This parameter is optional and can be used tospecify the minimum longitude of the usefulrange of the coordinate system. The value isgiven in degrees relative to Greenwich. Positivevalues indicate east longitude, while negativevalues indicate west longitude. Its value shouldbe normalized between -360 and +360 and,when used, must be algebraically less than theMAX_LNG parameter.

Yes

MAX_LAT This parameter is optional and can be used tospecify the maximum latitude of the useful rangeof the coordinate system. The value is given indegrees relative to the equator. Positive valuesindicate north latitude while negative values indi-cate south latitude. Its value should be nor-malized between -90 and +90 and when usedmust be algebraically greater than the MIN_LATparameter.

Yes

MIN_LAT This parameter is optional and can be used tospecify the minimum latitude of the useful rangeof the coordinate system. The value is given indegrees relative to the equator. Positive valuesindicate north latitude while negative values indi-cate south latitude. Its value should be nor-malized between -90 and +90 and, when used,must be algebraically less than the MAX_LAT parameter.

Yes

MAX_XX This parameter is optional and can be used tospecify the maximum X coordinate value of theuseful range of the coordinate system. The valueis given in system units. Its value must be alge-braically greater than the MIN_XX parameter.

Yes

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Name Range Description Optional?

MIN_XX This parameter is optional and can be used tospecify the minimum X coordinate value of theuseful range of the coordinate system. The valueis given in system units. Its value must be alge-braically less than the MAX_XX parameter.

Yes

MAX_YY This parameter is optional and can be used tospecify the maximum Y coordinate value of theuseful range of the coordinate system. The valueis given in system units. Its value must be alge-braically greater than the MIN_YY parameter.

Yes

MIN_YY This parameter is optional and can be used tospecify the minimum Y coordinate value of theuseful range of the coordinate system. The valueis given in system units. Its value must be alge-braically less than the MAX_YY parameter.

Yes

ORG_LAT Used to specify the origin latitude of the coor-dinate system. This value is specified in degreesrelative to the equator. Use positive numbers fornorth latitude, negative numbers for south lat-itude.

Yes

ORG_LNG Used to specify the origin longitude of the coor-dinate system. This value is specified in degreesand is always relative to the Greenwich primemeridian. Use positive numbers for east lon-gitude, negative numbers for west longitude.

Yes

PARM1 thru PARM24 Depends on theprojection system – seeProjection Types.

These parameters specify the value of as many as24 parameters which are specific to the particularprojection in use. The use of these items variesfrom one projection to another.

No

PROJ See Projection Types. This parameter specifies the type of mapprojection used for this definition. This namemust come from the Projection Types table and itdetermines which other parameters may be spec-ified. The parameters used by each projectiontype linked to this table.

No

QUAD -4..4 This parameter specifies the quadrant of the Car-tesian coordinates produced by the coordinatesystem. SeeQuadrant.

Yes

SCL_RED Used to specify the scale reduction which mayapply to a coordinate system. This value isignored by the many projections which do notsupport this feature. The value may be specifiedas a decimal number, e.g. 0.9996, or as a ratio,e.g. 1:2500. A value of 1.0 or greater is unusual,but is accepted.

Yes

SOURCE any string This parameter specifies the person or agencysupplying the definition.

Yes

UNIT See Coordinate Units This parameter specifies the name of the units No

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Name Range Description Optional?

Supported. used to measure coordinates in the coordinatesystem.

X_OFF Used to specify the value of the false easting ofthe coordinate system. A value of 0.0 is assumedif no specification is made.

Yes

Y_OFF Used to specify the value of the false northing ofthe coordinate system. A value of 0.0 is assumedif no specification is made.

Yes

ZERO_X any non-negativenumber

Used to specify the minimum X value which is tobe considered non-zero. X coordinate valueswhose absolute value is less than the value spec-ified here will be converted to hard zeros. This isused to suppress coordinate output such as4.3472E-07 which can be of value in certain appli-cations. A value of 0.0 is assumed if no spec-ification is made.

Yes

ZERO_Y any non-negativenumber

Used to specify the minimum Y value which is tobe considered non-zero. Y coordinate valueswhose absolute value is less than the value spec-ified here will be converted to hard zeros. This isused to suppress coordinate output such as4.3472E-07 which can be of value in certain appli-cations. A value of 0.0 is assumed if no spec-ification is made.

Yes

Generic Parameters

Parameter Name Required/Optional Description

DESC_NM Optional Used to specify the 63 character descriptive name of the coordinate system beingdefined.

DT_NAME Required unless EL_NAMEis specified

Used to specify the datum key name to which a geodetically referenced coordinate sys-tem is to be referenced to. The ellipsoid used is a part of this datum definition. Pres-ence of a valid datum key name here indicates that the coordinate system isgeodetically referenced. Either a DT_NAME specification, or an EL_NAME specificationmust be provided for each coordinate system definition. If both DT_NAME and EL_NAME specifications are provided, the EL_NAME specification is ignored.

EL_NAME Required unless DT_NAMEis specified

Used to specify the ellipsoid key name for a cartographically referenced coordinatesystem. A coordinate system is cartographically referenced to the ellipsoid named bythis specification if, and only if, the datum key name specification is omitted. If bothDT_NAME and EL_NAME specifications are provided, the EL_NAME specification isignored.

ORG_LAT Optional Used to specify the origin latitude of the coordinate system. This value is specified indegrees relative to the equator. Use positive numbers for north latitude, negativenumbers for south latitude.

ORG_LNG Optional Used to specify the origin longitude of the coordinate system. This value is specifiedin degrees and is always relative to the Greenwich prime meridian. Use positivenumbers for east longitude, negative numbers for west longitude.

SCL_RED Optional Used to specify the scale reduction which may apply to a coordinate system. Thisvalue is ignored by the many projections which do not support this feature. The valuemay be specified as a decimal number, e.g. 0.9996, or as a ratio, e.g. 1:2500. Avalue of 1.0 or greater is unusual, but is accepted.

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ZERO_X Optional Used to specify the minimum X value which is to be considered non-zero. X coor-dinate values whose absolute value is less than the value specified here will be con-verted to hard zeros. This is used to suppress coordinate output such as 4.3472E-07which can be of value in certain applications. A value of 0.0 is assumed if no spec-ification is made.

ZERO_Y Optional Used to specify the minimum Y value which is to be considered non-zero. Y coor-dinate values whose absolute value is less than the value specified here will be con-verted to hard zeros. This is used to suppress coordinate output such as 4.3472E-07which can be of value in certain applications. A value of 0.0 is assumed if no spec-ification is made.

PARM1 thruPARM24

Optional Used to specify the value of as many as 24 parameters which are specific to the par-ticular projection in use. The use of these items varies from one projection to another.The value is always a real number. Where a longitude is specified, it must be given indegrees, relative to Greenwich, where west longitude and south latitude are negative.Where a latitude is expected, it must be given in degrees relative to the equator wherenorth latitude is positive and south latitude is negative. When an azimuth is spec-ified, it must be given in degrees east of north (i.e. west of north would be negative).

X_OFF Optional Used to specify the value of the false easting of the coordinate system. A value of 0.0is assumed if no specification is made.

Y_OFF Optional Used to specify the value of the false northing of the coordinate system. A value of 0.0is assumed if no specification is made.

PROJ Required Used to specify the code name of the projection upon which the coordinate system isbased.

UNIT Required Used to specify the name of the system unit for the coordinate system being defined.

GROUP Optional Used to classify coordinate systems into groups to make selection of a coordinate sys-tem from the 1,000+ provided a bit easier.

SOURCE Optional Used to specify the source of the information used to define this coordinate system,63 characters maximum.

QUAD Optional Used to indicate the quadrant of the cartesian coordinates produced by the coordinatesystem. Zero or 1 indicate the normal right handed cartesian system where Xincreases to the east, and Y increases to the north. Quadrants are numbered counter-clockwise, therefore a value of 2 specifies a cartesian system where X increases to thewest, while Y increases north. A value of 3 indicates that X increases to the west andY increases to the south. A value of 4 indicates that X increases to the east and Yincreases to the south. A negative value will cause the axes to be swapped after theappropriate quadrant is applied. A value of 1 is assumed if this specification isabsent.

MIN_LNG Optional This parameter is optional and can be used to specify the minimum longitude of theuseful range of the coordinate system. The value is given in degrees relative to Green-wich. Positive values indicate east longitude, while negative values indicate west lon-gitude. Its value should be normalized between -360 and +360 and when used mustbe algebraically less than the MAX_LNG parameter.

MAX_LNG Optional This parameter is optional and can be used to specify the maximum longitude of theuseful range of the coordinate system. The value is given in degrees relative to Green-wich. Positive values indicate east longitude, while negative values indicate west lon-gitude. Its value should be normalized between -360 and +360 and when used mustbe algebraically greater than the MIN_LNG parameter.

MIN_LAT Optional This parameter is optional and can be used to specify the minimum latitude of the use-ful range of the coordinate system. The value is given in degrees relative to theequator. Positive values indicate north latitude while negative values indicate south lat-itude. Its value should be normalized between -90 and +90 and when used must bealgebraically less than the MAX_LAT parameter.

MAX_LAT Optional This parameter is optional and can be used to specify the maximum latitude of the use-ful range of the coordinate system. The value is given in degrees relative to the

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equator. Positive values indicate north latitude while negative values indicate south lat-itude. Its value should be normalized between -90 and +90 and when used must bealgebraically greater than the MIN_LAT parameter.

MIN_XX Optional This parameter is optional and can be used to specify the minimum X coordinate valueof the useful range of the coordinate system. The value is given in system units. Itsvalue must be algebraically less than the MAX_XX parameter.

MAX_XX Optional This parameter is optional and can be used to specify the maximum X coordinatevalue of the useful range of the coordinate system. The value is given in system units.Its value must be algebraically greater than the MIN_XX parameter.

MIN_YY Optional This parameter is optional and can be used to specify the minimum Y coordinate valueof the useful range of the coordinate system. The value is given in system units. Itsvalue must be algebraically less than the MAX_YY parameter.

MAX_YY Optional This parameter is optional and can be used to specify the maximum Y coordinatevalue of the useful range of the coordinate system. The value is given in system units.Its value must be algebraically greater than the MIN_YY parameter.

Allowed Projection Types

Each coordinate system definition must specify a projection type and provide values for all of the parameters associated with the projection.

The table below lists the projection types allowed in coordinate system definitions.

Notes

l All latitudes and longitudes provided as projection parameters must be given in degrees. Negative values areused to indicate southern latitude and western longitude.

l All longitude values must be given relative to the Greenwich Prime Meridian.

l False origins are always given in the units of the coordinate system.

Projection Type Description

AE Albers Equal Area

AZMEA Lambert Azimuthal Equal Area

AZMED Lambert Azimuth Equidistant

AZMED-ELEV Lambert Azimuthal Equidistant, Elevated Ellipsoid

BIPOLAR Bipolar Oblique Conformal Conic

BONNE Bonne

CASSINI Cassini

ECKERT4 Eckert 4

ECKERT6 Eckert 6

EDCNC Equidistant Conic

EDCYL Equidistant Cylindrical

EDCYL-E Equidistant Cylindrical Projection (Ellipsoidal or Spherical)

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Projection Type Description

GAUSSK Gauss Kruger Projection, aka Gauss

GEOCENTRIC_FME Geocentric

GNOMONIC Gnomonic

GOODE Good Homolosine

HOM1UV Hotine Oblique Mercator – one point, unrectified

HOM1XY Hotine Oblique Mercator, Alaska Variation

HOM2UV Hotine Oblique Mercator – two points, unrectified

HOM2XY Hotine Oblique Mercator – two points, rectified

KROVAK Krovak Oblique Conformal Conic, Czechoslovkia

KROVAK95 Krovak Oblique Conformal Conic, Czechoslovkia, 1995 Adjustment

LL Latitude/Longitude

LM Lambert Conformal Conic

LM1SP Lambert Conformal Conic Projection, One Standard Parallel

LMAF Lambert Conformal Conic (2SP) with Affine Post Process

LMBLGN Lambert Conformal Conic Projection, Belgian Variation

LM-MNDOT Lambert Conformal Conic, Minnesota DOT Variation

LMTAN Lambert Tangential

LM-WCCS Lambert Conformal Conic, Wisconsin County Variation

MILLER Miller Cylindrical

MODPC Modified Polyconic

MOLLWEID Mollweide Projection

MRCAT Mercator Cylindrical Projection with Standard Parallel (Tradi-tional)

MRCAT-PV Popular Visualisation Pseudo Mercator

MRCATK Mercator Cylindrical Projection with Scale Reduction

MSTERO Modified Stereographic

NEACYL Normal Aspect Equal Area Cylindrical

NERTH NonEarth

NERTH-SRT NERTH-SRT

NZEALAND New Zealand National Grid

OBQCYL Oblique Cylindrical

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Projection Type Description

ORTHO Orthographic

OSTERO Oblique Stereographic (International)

OSTEROUS Oblique Stereographic (per Snyder USA)

OSTN02 ETRF89 Referenced OSGB

OSTN97 ETRF89 Referenced OSGB (ETRF89<-->OSGB via OSTN97)

PCARREE Plate Carree / Simple Cylindrical

PLYCN American Polyconic

PSTERO Polar Stereographic Projection

ROBINSON Robinson

RSKEW Rectified Skew Orthomorphic, Azimuth at Projection Center

RSKEWC Rectified Skew Orthomorphic, Origin and Azimuth at Center

RSKEWO Rectified Skew Orthomorphic, Skew Azimuth at Rectified Origin

SINUS Sinusoidal

SOTM South-Oriented Transverse Mercator

SWISS Swiss Oblique Cylindrical Projection

SYSTM34 Danish System 34, UTM + polynomials (pre-1999 vintage)

SYSTM34-01 Danish System 34, UTM + polynomials (2001 vintage)

SYSTM34-99 Danish System 34, UTM + polynomials (1999 vintage)

TEACYL Transverse Aspect Equal Area Cylindrical

TM Transverse Mercator

TMAF Transverse Mercator (Gauss/Kruger) with Affine Post Process

TM-MNDOT Transverse Mercator, Minnesota DOT Variation

TM-SNYDER Transverse Mercator per J. P. Snyder

TM-WCCS Transverse Mercator, Wisconsin County Variation

UTM Universal Transverse Mercator System

VDGRNTN Van Der Grinten

Defining New Ellipsoids

Certain sites may require an ellipsoid that is not predefined in the FME. In such a case, a custom ellipsoid may be created. Ellipsoid definitionsmay occur in an FME mapping file, as well as in the LocalCoordSysDefs.fme. The syntax of an ellipsoid definition is:

ELLIPSOID_DEF <ellipsoidName> \DESC_NM <descriptive name> \SOURCE <source> \

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E_RAD <equator radius> \P_RAD <polar radius>

Example Ellipsoid Definition

This mapping file fragment defines a sample ellipsoid:

ELLIPSOID_DEF myEllipse \DESC_NM “Safe Sample Ellipse” \SOURCE “Safe Software Inc.” \E_RAD 6377340.128 \P_RAD 63356034.448

Ellipsoid Definition Parameters

Name Range Description Optional

<ellipsoidName> any string The name of the ellipsoid being de-fined. No

<descriptivename>

any string A descriptive name for the ellipsoid. Yes

<source> any string The individual or agency providing the ellipsoid param-eters.

Yes

<equator radius> floating pointvalue

The radius of the ellipsoid in metres at the equator. No

<polar radius> floating pointvalue

The radius of the ellipsoid in metres in the polar direc-tion.

No

How FME Manages Grid Shift Files

Grid shift files are used when reprojecting between coordinate systems that have different datums.

FME supports conversions between coordinate systems using different datums. Many datum transformations are not mathematically definableand require the use of grid of shifts. If you attempt to make a datum transformation of this kind without the appropriate grid shift file in place,FME will abort the translation.

The FME installation includes a configuration file for managing the use and location of grid shift files.

These files are found in the Reproject directory in the FME installation directory. For example, the file Nad27ToNad83.gdc includes filepaths to both the Canadian and US grid shift files for the NAD27 <-> NAD83 transformations.

Included Grid Shift Files

Adding Grid Shift Files

Coordinate Systems

Which files are included with FME?

When you install FME, grid shift files for the following datum transformations are automatically installed:

l AGD66 <-> GDA94 (Australia)l AGD84 <-> GDA94 (Australia)l CH1903 <-> CH1903Plus (Chenyx06, Switzerland)l DHDN <-> ETRS89 (BeTA2007, Germany)l DHDN <-> ETRS89 (SeTa2009, Germany)l ED50 <-> ETRF89 (Spain)

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l NAD27 <-> NAD83 (Canada)l NAD27 <-> NAD83 (USA)l NGVD29 <-> NAVD88 (VERTCON, USA, for use with NAD27 <-> NAD83 above)l NAD83 <-> HPGN (United States)l NAD83 <-> NAVD88 (Orthometric Geoid96/99/03, USA)l NTF <-> RGF93 (France)l NZGD49 <-> NZGD2K (New Zealand)l OSGB <-> OSTN97 (Great Britain)l OSGB <-> OSTN02 (Great Britain)l TOKYO <-> TOKYO GRID (Japan)l WGS84 <-> EGM96 (Orthometric WW15MGH, World)

Unsupported Transformations

Please note that different jurisdictions and standards may require the use of specific grid shift files not necessarily provided by Safe Software.Safe is unable to provide grid shift files for the transformations listed below. In these cases, it is necessary to contact the appropriate juris-diction to obtain the required files.

l NAD27 <-> CSRS (Canadian provinces)

l NAD83 <-> CSRS (Canadian provinces)

l ATS77 <-> CSRS (Province of New Brunswick)

l NAD27 <-> ATS77 (Province of New Brunswick)

To obtain grid shift files for Canadian CSRS and ATS77 transformations, Provincial contacts are available here:

http://www.geod.nrcan.gc.ca/contact2_e.php

Adding support for NAD83 <-> NAD27 Datum Shifts

You cannot perform implicit NAD83 <-> NAD27 datum shifts until Canadian or U.S. grid files have been chosen.

In FME, you can specify the grid files to use. From the Workbench menu bar, click Tools > FME Options and then click the Coordinate Systemsicon.

It is not necessary to choose grid files using this method if a NAD83 <-> NAD27 transformation is explicitly chosen in a CsmapReprojectortransformer.

USE Data Transformation Approximations

For more information on individual grid shift files, see USE Data Transformation Approximations.

Adding and Maintaining Grid Shift Files

Follow these steps to install a grid file so that FME will recognize the file:

1. Select Tools > FME Options and click the Coordinate Systems icon.

2. Select the applicable datum shift and click the Edit button.

3. A dialog displays the files already recognized by FME for the applicable datum shift. To include new files, click the Add button, browse tothe applicable directory.

4. Select the file and click OK.

Maintaining Grid Shift Files

See Setting Coordinate System Options.

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Datum Definition

Certain sites may require a datum that is not predefined in FME. In such a case, a custom datummay be created. Datum definitions may occurin an FME mapping file, as well as in the LocalCoordSysDefs.fme file. The syntax of a datum definition is:

DATUM_DEF <datumName> \

   DESC_NM <descriptive name> \

SOURCE <source> \

ELLIPSOID <ellipsoid name>  \

USE <use type>                \

DELTA_X <x value>             \

   DELTA_Y <y value>             \

   DELTA_Z <z value>             \

   BWSCALE <bwscale>             \

   ROT_X <rotX>                  \

   ROT_Y <rotY>                  \

   ROT_Z <rotZ>

DATUM_DEF DHDN \DESC_NM“Deutsches Hauptdreicknetz (DHDN)” \SOURCE“German Government” \ELLIPSOIDBESSEL \USEBURSA \DELTA_X582.00000000000 \DELTA_Y105.00000000000 \DELTA_Z414.00000000000 \BWSCALE8.3000000000000ROT_X-1.0400000000000ROT_Y-0.35000000000000ROT_Z3.0800000000000

Example datum definition

This mapping file fragment defines a datum with the BURSA use-type:

DATUM_DEF DHDN \DESC_NM “Deutsches Hauptdreicknetz (DHDN)” \SOURCE “German Government” \ELLIPSOID BESSEL \USE BURSA \DELTA_X 582.00000000000 \DELTA_Y 105.00000000000 \DELTA_Z 414.00000000000 \

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BWSCALE 8.3000000000000ROT_X -1.0400000000000ROT_Y -0.35000000000000ROT_Z 3.0800000000000

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Datum Definition Parameters

Name Range Description Optional

<datumName> any string The name of the datum being defined. No

<descriptive name> any string A descriptive name for the datum. Yes

<source> any string The individual or agency providing the datumparameters. Yes

<ellipsoid name> valid ellipsoid The ellipsoid upon which the datum is based. No

<use type>

3PARAMETER4PARAMETER6PARAMETER7PARAMETERAGD66AGD84ATS77BURSACSRSDHDNGDA94HPGNJGD2KMOLODENSKYMULREGNAD27NAD83NZGD2KNZGD49WGS72WGS84

The type of approximation used when the datumis involved in a datum conversion. No

<x value> floating pointvalue

The X component of the vector from the geo-center of the datum being defined to the geo-center of the WGS-84 datum.Units: meters.

No

<y value> floating pointvalue

The Y component of the vector from the geo-center of the datum being defined to the geo-centre of the WGS-84 datum.

Units: meters.No

<z value> floating pointvalue

The Z component of the vector from the geo-center of the datum being defined to the geo-center of the WGS-84 datum.

Units: meters.

No

<bwscale> floating pointvalue

The scale factor employed by the BURSA use-type, in parts per million.

Not used by all datum types.

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<rotX> floating pointvalue

The X rotation factor employed by the BURSAuse-type.

Units: Seconds of arc.

Not used by all datum types.

<rotY> floating pointvalue

The Y rotation factor employed by the BURSAuse-type.

Units: Seconds of arc.

Not used by all datum types.

<rotZ> floating pointvalue

The Z rotation factor employed by the BURSAuse-type.

Units: Seconds of arc.

Not used by all datum types.

Datum Transformations

This topic describes the nature and applicability of the geodetic transformation techniques supported by the coordinate conversion system. TheUSE clause present in each datum definition identifies the technique that will be applied to transform coordinates between datums.

With few exceptions, the geodetic transformation is a mathematical process by which geographic coordinates are converted from some datumto the WGS84 reference ellipsoid.

Geodetic Transformation Method Description

AGD66 to GDA94 via Grid File The Australians have adopted the techniques developed by Geomatics Can-ada for its National Transformation (Version 2) to define a precise means ofconverting from the Australian Geodetic Datum of 1966 to the newer Geo-centric Datum of Australia 1994. The data files involve overlap, and thoseareas deserve special attention.Datum shift data files for this transformation are being developed on astate-by-state basis. Therefore, there is more than one data file for thistransformation. The coordinate conversion system considers AGD66 to be asingle entity even through there are several different data files that over-lap. Users are encouraged to sort data files to ensure that the desired datafile is used in the regions of overlap.

AGD84 to GDA94 via Grid File Several of the states in Australia have been using the Australian GeodeticDatum of 1984 for some time now. This transformation technique imple-ments the conversion of AGD84 to GDA 1994. Operationally, this techniqueis identical to the AGD66 to GDA94; however, different data files are used.See AGD66 to GDA94 via Grid Fileabove for more details.

ATS77 to CSRS via Grid File The Average Terrestrial System of 1977 has been used in the Maritime prov-inces of Canada since 1977. This transformation uses data files in the Cana-dian National Transformation (version 2) format to determine the shiftrequired to properly transform ATS77-based geographic coordinates toCSRS-based coordinates. Note that:

l each of the different provinces involved have produced a data file covering the geog-raphy of their respective provinces, and

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Geodetic Transformation Method Description

l the individual data files are not in the public domain and must be obtained by usersdirectly from the provincial governments involved.

Bursa/Wolf Transformation This transformation is actually an approximation of the Seven ParameterTransformation

The approximation is arrived at by making three assumptions:

1. the sine of a small angle is equal to the angle (in radians) itself;

2. the multiplication of two sine terms is zero; and

3. the cosine of a small angle is one.

This approximation is valid only for small angles.

In all other aspects, this transformation is the same as the Seven Parameter transformation. Inprocessing new data projects, use the Seven Parameter transformation in lieu of theBursa/Wolf. The Bursa/Wolf approximation is provided for purpose of providing the means toreproduce numbers/calculations that were originally accomplished using the approximation.

CH1903 to CH1903+ via Grid File Switzerland has adopted the Canadian technique to define the shift fromCH1903 to CH1903+.

CSRS to NAD27 via Grid Files CSRS (Canadian Spatial Reference System) is the Canadian equivalent tothe U.S.'s HARN; that is, a very accurate rework of NAD83 using GPS tech-nology. This transformation allows direct conversion of NAD27 data toCSRS, without making a stop at NAD83. This conversion technique is imple-mented by a series of datum shift grid files of the Canadian National Trans-formation format. Unlike other implementations by Canadians, however,there are multiple overlapping files involved.You can choose a fallback transformation to specify how data points outsidethe coverage of existing data files are to be handled. Again, the data filesare being generated on a province-by-province basis. The individual filesmay, or may not, be in the public domain. You may need to acquire theappropriate data files yourself in order to use the transformation.

CSRS to NAD83 via Grid Files CSRS (Canadian Spatial Reference System) is the Canadian equivalent tothe U.S.'s HARN; that is, a very accurate rework of NAD83 using GPS tech-nology. Like the US HARN, the shifts are in the range of 1 to 2 feet(40 centimeters).This conversion technique is implemented by a series of datum shift gridfiles of the Canadian National Transformation format. Unlike other imple-mentations by Canadians, however, there are multiple overlapping filesinvolved.You can choose a fallback transformation to specify how data points outsidethe coverage of existing data files are to be handled.Again, the data files are being generated on a province-by-province basis.The individual files may, or may not, be in the public domain. You may needto acquire the appropriate data files yourself in order to use the trans-

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Geodetic Transformation Method Description

formation.

DHDN to ETRS89 via Grid File German authorities have published a grid shift data file for transformingDHDN to ETRS89, applicable to German geography. Although this file coversall of Germany, it is appropriate only for specific uses.

Note that the official name may use the designation ETRF89 instead of ETRS89.

ED50 to ETRF89 via Grid Files Spain has also adopted the Canadian technique to define the shift from theEuropean Datum of 1950 (ED50) to European Terrestrial Reference Frame,1989 (ETRF89).

ETRF89 No Shift Required At the current time, the differences between ETRF89 and WGS84 are small.Further, a generally accepted means of converting between ETRF89 andWGS84 is unknown to the authors of the coordinate conversion system. Thistechnique does nothing.

Four Parameter Transformation This transformation is the Seven Parameter Transformation without the Rota-tion parameters. You could achieve the same results by using the SevenParameter Transformation, setting the three rotation parameters to zero,and setting the remaining four parameters as appropriate.

GDA94, No Shift Required The differences between GDA94 and WGS84 are small. Further, a generallyaccepted means of converting between GDA94 and WGS84 is unknown tothe authors of the coordinate conversion system.

Geocentric Transformation This transformation will produce the same results as the Seven ParameterTransformation with all three rotation parameters and the scale parameterset to zero.As with the Seven Parameter Transformation, this transformation proceedsin three phases. First, the geographic coordinates are converted to three-dimensional Cartesian, geocentric coordinates using the ellipsoid of the orig-inal datum. Second, the three translation parameters, Delta X, Delta Y, andDelta Z, are used to translate the geocentric coordinates. Third, the result-ing geocentric coordinates are converted back to geographic form using thetarget ellipsoid.As in all other cases for the translation parameters, the geocentric param-eters must be given in units of meters.

Grid Interpolation This transformation method supports a priority ordered list of grid files inarbitrary formats. It is specific to geodetic transformation definitions, andmay not be used for datums. Each grid file entry includes the grid format,direction of the grid, and the path to the grid. The first grid that providescoverage of the input point will be used for conversion.Grid Formats:

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Geodetic Transformation Method Description

Format Name Format Description Notes

NTv1 Canadian National Transformation, Ver-sion 1

NTv2 Canadian National Transformation, Ver-sion 2

NADCON US NADCON (i.e., las/los pair) Only a single entry shouldbe added for each las/lospair. (e.g., arhpgn.l?s)

FRGEO French Geocentric Interpolation

JPPAR Japanese Grid Mesh Interpolation (i.e..par)

ATS77 Maritime Provinces Polynomial Inter-polation

Grid direction must be ‘Fwd’ (Forward) or ‘Inv’ (Inverse/Reverse).Transformation Definition Example Snippet:

[…]

METHOD GRID_INTERP \

GRID_FILE “NADCON,Fwd,.\GridData\Nadcon\arhpgn.l?s” \

GRID_FILE “NADCON,Fwd,.\GridData\Nadcon\alhpgn.l?s”

HARN to NAD83 via NADCON HARN (High-Accuracy Reference Network) has also been known as HPGN(High-Precision GPS Network): both terms refer to NAD83/91, which is arework of NAD83 with the aid of GPS technology (since GPS was not func-tional in 1983). This technique selection implies the use of the algorithmsand data files of the U. S. National Geodetic Survey's NADCON program toeffect the shift between NAD83 and HARN.As with the NADCON technique this transformation relies on the existence ofdata files that define the shift at various geographic points in a grid format.As is the case with the NAD27/NAD83 NADCON data files, these data filescome in pairs and are in the public domain.All of the data files used in this transformation adhere to a specific namingconvention (as published by the National Geodetic Survey): they must havethe proper .LAS and .LOS extensions, and the names and locations must beproperly recorded in the Geodetic Data Catalog file. These files all overlaptheir neighbors by a substantial amount.Since different results for the same point can be obtained depending uponwhich specific data files are used, users should pay significant attention tothe order and choice of files. For example, if the geography one is workingis primarily in Ohio, then the Ohio HPGN file should be listed first in the cat-alog file. This will cause that data file to take precedence over all others inthe case of overlap.

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Geodetic Transformation Method Description

Users can choose a fallback transformation to specify a fallback definitionto be used when coordinate data not covered by the data files is processed.

JGD2K via Grid Files This method is used to transform data from the older Tokyo Datum to theJapanese Geodetic Datum of 2000 (JGD2K). Associated data files define thetransformation, and must be purchased from the Geographic Institute ofJapan.The data files, as supplied by the Geographic Institute of Japan, are in theform of text files, with no guarantee of records of fixed length, and whichare not in any specific order. Since the most popular of these files covers allof Japan, the size of this particular file is quite large (approximately 12 MB).FME will, therefore, convert the text file into a binary form upon its firstuse.

Local DHDN to ETRS89 via Grid File The local DHDN to ETRS89 grid shift is used to transform coordinates in amore precise scale than the “DHDN to ETRS89” grid shift and does not nec-essarily cover all of Germany.This transformation must be configured to point to the user-provided GridShift Binary (gsb) files required to execute the particular NTv2 transformrequired. To make the change, click Tools > FME Options > CoordinateSystems.The USE method for this datum is DHDN_LOCAL. The corresponding trans-formation name is DHDN/local_FME_to_ETRS89/01.

MGI to ETRS89 via Grid File Austrian authorities have published a grid shift data file for transformingMGI to ETRS89, applicable to Austrian geography. This covers all of Austria.This transformation must be configured to point to the Grid Shift Binary fileAT_GIS_GRID.gsb. To make the change, click Tools >FME Options > Coor-dinate Systems. You can also just place the AT_GIS_GRID.gsb file in thedefault location:

<FME Install Directory>/Reproject/GridData/Austria/AT_GIS_GRID.gsb.

This file, available freely at the website of the Austrian Federal Office forMetrology and Survey, http://www.bev.gv.at, is required to execute the par-ticular NTv2 transform required.The USE method for this datum is MGI. The corresponding transformationname is MGI/Grid_FME_to_ETRS89/01.

Molodensky This transformation is the DMA (US Defense Mapping Agency [now knownas NIMA]) implementation of the Molodensky transformation. (The formulasused were extracted from Defense Mapping Agency Technical Report8350.2-B, 1 December 1987.) Effectively, it is a variation of the GeocentricTransformation that produces very similar results and can be calculated with-out iteration. Most importantly, the parameter use for this transformation is

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Geodetic Transformation Method Description

the same as the Three Parameter Transformation.

Molodensky-Badekas Transformation In addition to the Seven Parameter Transformation parameters, Molodensky-Badekas allows a rotation origin point to be specified. The additional param-eters are:

Rotation Origin X: The X component of the point (in the source Cartesian coordinate ref-erence system) about which the rotation will be performed.

Rotation Origin Y: The Y component of the point (in the source Cartesian coordinate ref-erence system) about which the rotation will be performed.

Rotation Origin Z: The Z component of the point (in the source Cartesian coordinate ref-erence system) about which the rotation will be performed.

Multiple Regression ala DMA This transformation is based on the series of Multiple Regression devel-opments published by the US Defense Mapping Agency (NIMA) in TechnicalReport 8350.2-B, December 1987. Essentially, these are formulas devel-oped from applying linear regression techniques to a varying number ofpoints where the source and target ellipsoid coordinates are rather pre-cisely known.These regression formulas are based on normalized input coordinates. It isassumed that the normalized coordinates define the useful range of thedatum transformation. In theory, therefore, a geographic coordinate thatproduces a normalized coordinate greater than 1.0 or less than -1.0 wouldnormally be considered to be outside the useful range of the trans-formation. In this implementation of the regression technique, a geographiccoordinate is considered to be outside the useful range of a transformationif the absolute value of either normalized coordinate exceeds 1.4.In the event that a coordinate is given that is outside of the useful range ofthe multiple regression formula as described above, a fallback technique isused to calculate a datum shift. In this case, the fallback technique is theMolodensky, the Six Parameter Transformation, or the Seven ParameterTransformation depending upon how many parameters have been defined inthe base definition. That is, when defining the datum definition, temporarilyset the technique specification to Seven Parameter and set the desired fall-back parameters. Then, the technique can be set back to the MultipleRegression selection and the parameters values will be preserved.Currently, the parameters to such a transformation consist of a pre-processed transformation definition file. These files contain all of the coef-ficients of the multiple regression formula in a compact form. This formalso facilitates the actual testing of each parameter file individually as theDMA-provided test case is included in the file. Currently, no provisions aremade for users to implement their own multiple regression parameter files.This may change in the future.

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Geodetic Transformation Method Description

NAD27 to NAD83 via NADCON This transformation represents the integration of the algorithms originallypublished by the National Geodetic Survey of the US and Geomatics Canadain the forms commonly known as the NADCON program and the NationalTransformation (Versions 1 and 2). That is, this transformation is the meansby which one would convert from the North American Datum of 1927(NAD27) to the North American Datum of 1983 (NAD83).All of the techniques encapsulated in this transformation rely on access todata files that define the amount of the shift from NAD27 to NAD83 in a gridform. The coordinate conversion system uses algorithms identical to thoseused by the respective government-published programs to interrogate thedata files and determine the shift for any given coordinate.The shift data is stored in a single data file for the Canadian National Trans-formation (either version) and neither of these data files is in the publicdomain. The recommended NTv2 file is distributed with FME. In the case ofthe US NADCON data files, two files are required for each region covered.One file contains the latitude shift and the second contains the longitudeshift. These files are in the public domain and are usually included in the dis-tribution of this product. Should updates become available, you can use thedata files in the exact form as they are published by the National GeodeticSurvey.Since the coverage of the data files is limited, the coordinate conversionsystem uses a fallback technique to calculate datum shifts for coordinatesthat are not covered by the data files.

NAD83, No Shift Required For practical GIS applications, there is no difference between NAD83 andWGS84. Both are very precise measurements of the same thing, and whatdifferences there are between the two are largely due to how the statisticalnoise was handled. Also, there are no published techniques or generallyaccepted means of converting from NAD83 to WGS84. The end result of allthis is that this transformation does nothing.

NTF to RGF93 via Grid File France has developed a technique to define the shift from the New Tri-angulation of France Datum (NTF) to Reference Geodesique pour la France(RGF93). This technique makes use of a single grid file called gr3df97a.txtwhich must be placed in the FME's Reproject directory to work. For allintents and purposes, RGF93 is considered equivalent to WGS84.

NZGD2K, No Shift Required At the current time, the differences between NZGD2K and WGS84 are small.Further, a generally accepted means of converting between NZGD2K andWGS84 is unknown to the authors of the coordinate conversion system. Thistechnique does nothing.

NZGD49 to NZGD2K via Grid File New Zealand has also adopted the Canadian technique to define the shiftfrom the New Zealand Geodetic Datum of 1949 (NZGD49) to New Zealand

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Geodetic Transformation Method Description

Geocentric Datum of 2000 (NZGD2K). This implementation is somewhat sim-pler in that only a single data file is used.

ROME1940 to IGM95 via Grid File The ROME1940 to IGM95 grid shift is used to transform coordinates betweenthese two datums used in Italy.This transformation must be configured to point to the user-provided GridShift Binary file R40WGS_t.gsb required to execute the particular NTv2transform required. To make the change, click Tools > FME Options > Coor-dinate Systems. You can also just place the R40WGS_t.gsb file in the defaultlocation: <FME Install Direc-

tory>/Reproject/GridData/Italy/R40WGS_t.gsb.The USE method for this datum is ROME40. The corresponding trans-formation name is MonteMario_Grid_FME_to_IGM1995.

Seven Parameter Transformation This transformation is a rigorous implementation of the standard three-dimensional transformation. The seven provided parameters must indicatethe transformation to convert source datum coordinates to target datumcoordinates. For many typical GIS applications, you can simply change thesign of each of the seven parameters to affect an inverse. However, thistechnique is not exact. For precise results, a rigorous inversion is necessaryin order to determine the appropriate parameters.Essentially, this transformation proceeds in three phases. First, the geo-graphic coordinates are converted to three-dimensional Cartesian, geo-centric coordinates using the ellipsoid of the original datum. Second, thethree-dimensional transformation defined by the seven parameters isapplied producing a modified set of geocentric Cartesian coordinates. Third,the resulting geocentric coordinates are converted back to geographic formusing the target ellipsoid.The seven parameters are:Delta X: the amount the intermediary geocentric X coordinate is trans-lated. This value must be given in meters and the direction of the trans-lation is given by the sign of the value.Delta Y: the amount the intermediary geocentric Y coordinate is translated.This value must be given in meters and the direction of the translation isgiven by the sign of the value.Delta Z: the amount the intermediary geocentric Z coordinate is translated.This value must be given in meters and the direction of the translation isgiven by the sign of the value.X Rotation: the amount of rotation about the X axis which is applied to theintermediary geocentric coordinates. This value is given in seconds of arc,and the direction of the rotation is indicated by the sign of the value.Y Rotation: the amount of rotation about the Y axis which is applied to the

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Geodetic Transformation Method Description

intermediary geocentric coordinates. This value is given in seconds of arc,and the direction of the rotation is indicated by the sign of the value.Z Rotation: the amount of rotation about the Z axis which is applied to theintermediary geocentric coordinates. This value is given in seconds of arc,and the direction of the rotation is indicated by the sign of the value.Scale: a scale factor that is applied to the intermediary geocentric coor-dinates. The value is given as a value in parts per million and is the dif-ference of the actual scale factor and unity. For example, a value for thescale parameter of -2.5 produces an actual scale factor of 0.9999985. Thatis, the actual scale factor used is arrived at by multiplying the parametervalue by 1.0x10-06 and adding the result (algebraically) to 1.0.

Six Parameter Transformation This transformation is the Seven Parameter Transformation without the Scaleparameter. You could achieve the same results by using the Seven Param-eter Transformation, setting the scale parameter to zero, and setting theremaining six parameters as appropriate.

WGS72 to WGS84 via DMA Formula This transformation implements the formulas published by the U. S.Defense Mapping Agency in Technical Report 8350.2-B, December 1987 fortransforming WGS72-based geographic coordinates to WGS84-based coor-dinates. The transformation is hard-coded and does not require any param-eters.

WGS84, No Shift Required This is another transformation that essentially does nothing, silently (i.e., itdoes not return an error), and very quickly. The WGS84 datum definitionrefers to this transformation technique.

Defining Custom Units

FME defines a large number of units (for example, meters, US feet, degrees, radians, etc.). If your coordinate system is measured in a unit thatFME does not already know about, you can define the new unit.

Unit definitions may occur in an FME mapping file, as well as in the file:

LocalCoordSysDefs.fme

The syntax of a unit definition is:

UNIT_DEF <unit name> \UNIT_TYPE <unit type> \UNIT_ABBREVIATION <unit abbreviation> \UNIT_FACTOR <unit size>

Name Range Description Optional

<unit name> any string The name of the unit being defined. No

<unit type> ANGLE | LENGTH Specifies whether the unit meas-ures angles or lengths.

No

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<unit abbreviation> any string This abbreviation repre-sents theunit and may be used in coordinatesystem definitions instead of the<unitname>.

No

<unit size> Floating pointnumber

The size of a unit in metres if itmeasures length. If the unit meas-ures angle, then this is the size indegrees.

No

Example Unit Definition

In this example, we define the unit “GRIDUNIT” (abbreviated as “GRD”) where the unit length is 0.999738 meters.

UNIT_DEF GRIDUNIT \UNIT_TYPE LENGTH \UNIT_ABBREVIATION GRD \UNIT_FACTOR 0.999738

Predefined Units

The following table lists the predefined units available to measure coordinates.

For the Latitude/Longitude pseudo-projection, angular measurement units are used to measure the coordinates.

FME Unit Name Full Name Unit Length in Metres

BENOITCHAIN Benoit chain 20.11678249438

BenoitLink Benoit link 0.2011678249438

Brealey Brealey units 375.0

CAGRID Canadian grid unit 0.999738

CAPEFOOT Cape foot 0.3047972615

CENTIMETER centimeter 0.01

CLARKECHAIN Clarke chain 20.1166194976

CLARKEFOOT Clarke foot 0.3047972651151

CLARKELINK Clarke link 0.201166194976

FOOT US survey foot 0.30480060960121920243

GOLD_COAST_FOOT Gold Coast foot 0.30479971

GERMANMETER German meter 1.0000135965

GERMAN_LEGAL_ME German legal me 1.000013597

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GUNTERCHAIN Gunter chain 20.11684023368047

GUNTERLINK Gunter link 0.2011684023368047

IFOOT international foot 0.3048

IINCH international inch 0.0254

IMILE international mile 1609.344

INCH inch 0.0254000508001016002

INDIAN_YARD Indian yard 0.91439523

IYARD international yard 0.9144

KILOMETER kilometer 1000

METER meter 1.0

MILE mile 1609.34721869443738887477

MILLIMETER millimeter 0.001

NAUTM nautical mile 1852.0

ROD rod 5.02921005842012

ROOD South African rood 3.778266898

SEARSCHAIN Sears chain 20.11676512155

SEARSLINK Sears link 0.2011676512155

SEARSYARD Sears yard 0.914398414616029

YARD yard 0.91440182880365760731

Quadrants

FME also allows coordinate systems to be measured in quadrants other than the usual one where X increases to the east and Y increases to thenorth. The QUAD directive in a coordinate system definition is used to set the orientation of the coordinate system.

This directive takes an integer value from -4 to 4. 0 or 1 indicate the normal right-handed Cartesian system, where X increases to the east, andY increases to the north. This is the default quadrant.

Quadrants are numbered counterclockwise; therefore:

n a value of 2 specifies a Cartesian system where X increases to the west and Y increases to the north;

n a value of 3 indicates that X increases to the west, and Y increases to the south;

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n a value of 4 indicates that X increases to the east and Y increases to the south.

2 1

3 4

A negative value will cause the axes to be swapped after the appropriate quadrant is applied.