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GIS DATA INPUT USINGGIS DATA INPUT USING

SCANNERS ANDSCANNERS ANDDIGITIZERSDIGITIZERS

Charles Redd & Nathan Miller Charles Redd & Nathan Miller

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First Some HistoryFirst Some History

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The Beginning ?The Beginning ?

GIS was born in Canada in the 1960¶s tomanage Canada¶s large natural resources.

The success of the merger of computers,database, and mapmaking was a bigsuccess.

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Did GIS Make 2,500 plus Years of Did GIS Make 2,500 plus Years of

Documents & MapmakingDocuments & MapmakingSuddenly ObsoleteSuddenly Obsolete ??From cave paintings to satellite images

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Hard Copy Data with GISHard Copy Data with GISSignificanceSignificance

Maps

Aerial Photos

Tables of spatial information (coordinates) Tables of Non-spatial informationattributes

Engineering and Architectural plans

Land and Geological Surveys

Caveman Drawings? Maybe

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How can we use preHow can we use pre--GIS data andGIS data andnonnon--digital data in our GISdigital data in our GIS

Digitize existing graphical information! ± Some of the first methods to digitize graphical

information involved overlaying the map with

a grid marked on a clear sheet of Mylar.Information that was within each grid wasvisually observed and entered by keyboardinto the GIS.

Attribute data from existing tables was handentered.

There must be a better way!

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Manual Digitizing ?Manual Digitizing ?

The majority of spatialdata entered into aGIS is from manual

digitizing.

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Manual DigitizingManual Digitizing

The digitizing tablet and table allowinformation to be traced from an existingmap or graphic.

Three different types of tables or tabletsexist. ± (1) Acoustic ± the digitizing pen emits a high

frequency sound that is received bymicrophones at the corners of the work area,triangulation is used to calculate the x and ycoordinate of the pen.

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GTCO CalComp Sonic Digitizer GTCO CalComp Sonic Digitizer

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Types of DigitizersTypes of Digitizers (Continued)(Continued)

(2) Resistivity uses two charged padsseparated by a thin air gap, x and ycoordinates are determined when the pads

make contact. (3) The most widely used in large scaledigitizers is the electronic digitizing tablet.Embedded below the surface of the table

or the tablet is a grid of wires that measurethe strength of the signal from the puck or the pen

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Qualities of a Digitizer Qualities of a Digitizer

± Stability

The ability of the digitizer to maintain avalue as the puck remains in one place.

± Repeatability

Precision

Good digitizers accurate to 0.001 inch

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Qualities of a Digitizer #2Qualities of a Digitizer #2

± Linearity

the ability to be within a specified distance

of the correct value Good digitizers are able to have a linearity

of 0.003 inch over 60 inches

± Skew

The ability to produce coordinates in a truerectangle.

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Digitizing ProceduresDigitizing Procedures

The Map is fixed to the digitizing table. Three or more control points are digitized.

± Easily identified points (intersections of major streets,major peaks, points on coastline)

± These coordinates will be known or verified ± The digitizing area is registered to the map area.

Digitizing the map can be done in two ways.

± In point mode , the operator identifies the points

captured explicitly by pressing a button. ± In stream mode the points are captured at regular

intervals (time or distance)

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Digitizing Procedures (cont)Digitizing Procedures (cont)

Point mode is done subjectively by theoperator (no two operators will digitize thesame).

Stream mode generates a large number of points, many of which will be redundant.

Most digitizing is done in point mode.

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Problems with DigitizingProblems with Digitizing

Paper maps are unstable, they stretch or shrink,sometimes while they are on the digitizing table.

The accuracy depends on the dedication of theoperator and his training and skill.

Accuracy also depends on the quality of thesource documents.

Paper maps weren¶t prepared ³digitally´ correct,but to visually impart information, for example if

railroads, highways and tunnels pass through amountain pass the pass may be drawn larger toaccommodate the drawing.

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Color Scanning TechnologyColor Scanning Technology

Color images use the same technique butthe image is scanned for red, blue andgreen.

Older scanners required the image beingscanned to pass the scanning head inthree passes.

Vectorization often requires color scanning

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Color Scanning TechnologyColor Scanning Technology

Filters allow the head to pass the imageonce scanning all three colors at once

The latest technology: full width, singleline, sensor array scanning uses a line of LED¶s which capture the image

LED scanners can create images using16.8 million colors at speeds several timesfaster than previously obtained.

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Scanning ProblemsScanning Problems

Higher resolutions aren¶t always the answer tobetter data; often the additional ³noise´ andresulting clean up of data can cause higher resolution to not be the best solution, a balance

between detail and additional manual clean-upmust be struck.

Paper maps are not ³dimensionally stable´ and agreat deal of variation occurs as the maps age.

Documents must be clean (no smudges or extramarks or lines).

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Scanning Problems #2Scanning Problems #2

Text may accidentally be scanned as linefeatures in automatic feature recognition.

Specialized symbols (for example marshor asphalt) may not be detected as such.

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IDEAL

Large FormatMonochrome Scanners

Model Pricemaxdpi

Paper Size Speed

FSS 4300DSP $6,675 200 36 in. 15 sec.

FSS 8300DSP $10,425 800 36 in.

17 sec.@200

dpi

FSS 12300DSP $11,925 1200 36 in.25 sec.@200dpi

FSS 18300DSP $13,425 1800 36 in.34 sec.@200dpi

Super Wide 2250 $13,425 400 50 in. 3 in./sec.

Super Wide 2251 $14,925 800 50 in. 6 in./sec

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ANAtechBinary & Grayscale Scanners

Evolution 4 $10,000 400 36 in.3"/sec @200 dpi

Evolution 8 $11,000 800 36 in.

3"/sec @

200 dpi

Evolution Pro $12,500 800 36 in.6.4"/sec @200 dpi

High ResolutionMonochrome Scanners

1270 Digidot $50,000 1270 27 in. Unknown

Eagle 4225 $55,000 2540 42 in. Unknown

Model Pricemaxdpi

Paper Size Speed

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Vendors for ScannersVendors for Scanners

Widecom Scanners ± www.widecom.com/

Anatech Scanners

± www.anatech.com/ Vidar Systems Corporation

± www.delinfotek.com/

Abakos Digital Images

± www.abakos.com.au/

Contex Scanning Technologies ± www.caddcentreindia.com/

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Digitizer or Scanner Digitizer or Scanner

Scanners

± Speed and ease

± Raster data without

intelligence; manual or automatic vectorisationpossible.

± Usually produces largefiles that needcompression

± Hardware is expensive

Digitizers

± Labor intensive

± Requires skilled

operator ± Vector (intelligent) data

± Labor intensive

± Hardware less

expensive

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Scanning & Digitizing Input ErrorsScanning & Digitizing Input Errors

Incompleteness of the spatial data;missing points, line segments, andpolygons.

Location placement errors of spatial data;careless digitizing or poor quality of theoriginal source.

Distortion of spatial data; base maps thataren¶t scale correct over the entire imageor from material stretch in paper maps.

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Scanning & Digitizing Input ErrorsScanning & Digitizing Input Errors#2#2

Incorrect linkage between spatial and attributedata; misplaced labels or unique identifiersbeing assigned during manual key entry or

during the initial setup. Attribute data is wrong or incomplete; missingdata records or data records from different timeperiods.

Redundant information, including vertices, text,nodes, and arcs.

Incorrect label information and placement.

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Common Spatial ErrorsCommon Spatial Errors

Slivers or gaps in the line work.

Dead ends, dangling arcs, overshoots and

undershoots. Bow ties or weird polygons caused by

inappropriate closings of connectingfeatures.

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Data VerificationData Verification

Visual review; usually done by reviewing a checkplot (hard copy).

Cleanup of lines and junctions; this process isusually done by software and then throughmanual editing.

Check source maps, if additional copies of thesame map are available compare them to see if stretching of the map has occurred.

Check output drawing to see if text or symbolswere read as features if software is used toconvert the drawings.

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Examples of Scanned andExamples of Scanned and Aerial images Aerial images

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Paris 1640Paris 1640

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Paris 2000Paris 2000

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Notre DameNotre Dame

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Summary of Presentation or«.Summary of Presentation or«.

Things I Learned Preparing thisThings I Learned Preparing thisReportReport

Scanning while initially faster may not be

the fastest solution for your data input. Source information needs to be carefully

assessed before a method of data

conversion is selected. The skill and motivation of staff should be

evaluated before a method is selected.

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OneOne Eagle 6250C Color Scanner Eagle 6250C Color Scanner Costs more than two Dodge VipersCosts more than two Dodge Vipers

Scanner $142,000

Two Vipers @ $69,225

= $138,450