Lec #7 Today's Topics (#7) Introduction to Topology - mysite tuaf

Fall 2013

LDA 150/ABT 150

3-Units

Introduction to

Geographic Information Systems (GIS)

Instructors:

Assoc.Prof. Dr. Dam Xuan VanTeaching Assistant

Msc. Nguyen Huy Trung

Lecture: Tuesday, D3O3 Hall, 8:55 AM – 10:45 AMLab Sections: Friday, computer lab 201, 8:55am – 10:45am

Lec #7Today’s Topics (#7)

• Topology

• Editing in ArcMap

• Polygon data layer creation process

Introduction to Topology

Recall: simple polygon (spaghetti model)

• All entities are represented by coordinate pairs

• Coordinate pairs must be in proper order

• This is a non-topological data structure

A

B

(5.1,2.3)

(6.2,3.3)

(6.6,1.4)

(4.8,1.3)

(5.7,0.2)

Polygon Coordinates

Polygon Coordinates

A (5.1,2.3) (6.2,3.3) (6.6,1.4) (4.8,1.3)B (4.8,1.3) (6.6,1.4) (5.7,0.2)

(Lo and Yeung p. 85)

(4.8, 1.3) (5.1, 2.3) (6.2, 3.3, (6.6, 1.4) (4.8, 1.3)

(4.8, 1.3)

*

Topological properties of consistent graphs

1) Every arc has 2 nodes (beginning and end)

2) Every arc separates 2 polygons

3) Every polygon is surrounded by a cycle of arcs and

nodes.

4) Every node is surrounded by a cycle of arcs and

polygons

5) Every intersection is at a node.

Note: outer (box) polygon is bounding space

= some

example

interior nodes

Every node is surrounded by a

cycle of arcs and polygons

Example of Property

#4:

Fundamental concepts of topology

• Connectivity

• Containment (area definition)

• Adjacency (contiguity)

Lo and Yeung p. 86

Connectivity

• Line segments connect to each other at a node or

a vertex. An arc is defined by two nodes: a start

node and an end node. Connected arcs are

determined by searching through an arc-node list

for matching node numbers.

• Implements topological properties 1 and 5:

– Every arc has 2 nodes

– Every intersection is at a node

Arc-node topology

(implements connectivity)

b

a

1

2

3

(5.1,2.3)

(6.2,3.3)

(6.6,1.4)

(4.8,1.3)

(5.7,0.2)

2. Arc Coordinate List

Arc # Coordinates

1 (4.8,1.3), (5.1,2.3), (6.2,3.3)

2 (4.8,1.3), (6.2,3.3)

3 (6.2,3.3), (5.7,0.2), (4.8,1.3)

(6.6, 1.4)

(6.6, 1.4)

(6.6, 1.4)

1.

1. Arc-Node List

Arc # From-nodeTo- node

1 a b

2 a b

3 b a

2.

Containment (Area definition)

• Closed, connected arcs surrounding an area define a polygon. The polygon is represented by its boundary arcs. A polygon whose boundary is inside that of a second is contained in the second.

• Implements topological property 3:

– Every polygon is surrounded by a cycle of arcs and nodes.

b

a

1

2

A

3

B

Polygon-arc topology

(implements containment)

3. Polygon-Arc List

Poly # Arcs

A 1, 2

B 2, 3

1. Arc-Node List

Arc # From-nodeTo- node

1 a b

2 a b

3 b a

2.

Adjacency

• Arcs have left and right sides. Left-right topology

refers to polygons on each side of an arc.

• Implements topological properties 2 and 4:

– Every arc separates 2 polygons

– Every node is surrounded by a cycle of arcs

and polygons

= some

example

interior nodes

Left-right topology

(implements adjacency)

b

a

1

2

A

3

B4. Left-Right List

Arc# L-Poly R-Poly

1 0 A

2 A B

3 0 B

3. Polygon-Arc List

Poly # Arcs

A 1, 2

B 2, 3

b

a

1

2

A

3

B

4. Left-Right List

Arc# L-Poly R-Poly

1 0 A

2 A B

3 0 B

3. Polygon-Arc List

Poly # Arcs

A 1, 2

B 2, 3

1. Arc-Node List

Arc # From-nodeTo- node

1 a b

2 a b

3 b a

Summary

2. Arc Coordinate List

Arc # Coordinates

1 (4.8,1.3), (5.1,2.3), (6.2,3.3)

2 (4.8,1.3), (6.2,3.3)

3 (6.2,3.3), (5.7,0.2), (4.8,1.3)

(6.6, 1.4)

(6.6, 1.4)

L&Y Fig 3.21

(6.6, 1.4)

connectivitycontainment

adjacency

1.

2.

Error checking by building topology

Building topology involves identifying all nodes, arcs,

and polygons

A

B

(5.1,2.3)

(6.2,3.3)

(6.6,1.4)

(4.8,1.3)

(5.7,0.2)

Zeiler 1999

Example topology in a TIN

Containment, connectivity, and adjacency

Common Topological Errors

Laurini and Thompson p. 191

4 common errors:

• Dangle

• Overshoot

• Overlap

• Nonsensical

vertex order

(ambiguity)

Topology_rules_poster.pdf 26 Rules

Identifies errors in Arc-Node topology

ExamplesIdentifies

polygon

containment

errors

Identifies

adjacency

errors

Identifies

point in

polygon

containment

errors

single

single

multiple

Working with map topology in

ArcGIS

• Topology rules are defined within a feature

dataset in a geodatabase

• The goal is to create a topologically

correct polygon data layer

– Unambiguous lines that define polygons

– No overshoots, undershoots, or overlaps

Vector Mapping

• Creation of feature classes

– Point, line or polygon

– Error checking

• An application of topology

• Creating the database

– Adding attributes manually

– Calculating attribute values

Example polygon feature class

The Land Cover Mapping Process

Red

Bluff

Colusa

Chico

Landing

Polygon feature class

creation process

1) Georeferencing a scan or air photo

2) Digitizing polylines

3) Edge matching • merge or append the data

4) Rubber sheeting

5) Topological validation• checks for line errors

6) Create polygons from polylines

7) Attribute the polygons in the database

8) Attribute error checking

Digitizing concepts and methods

• Creating entities: point, line, polygon

• The Editor Toolbar– Start Editing

– Choose the layer you wish to edit (in a Dialog Box)

– A “Create Features” template window appears and you click the symbol of the layer you wish to digitize on

– A drawing tool cross-hair appears and you can begin digitizing

• Minimum mapping unit (MMU) concept

• On projected imagery (e.g., DOQQs)

• Spatial data creation process– Digitizer tablet (“heads-down”) manual digitizing

– Scan-based (“heads-up”) manual digitizing

• Autovectorization (raster-to-vector conversion)– ArcScan extension

– Adobe Streamline

2. Vector Polyline Digitizing• Create a new feature class

– Create a blank shapefile or geodatabase layer in ArcCatalog

• Manual Methods:– Point-and-click mode to set points (point, line, polygon)

– Set snapping distance in the Snapping Toolbar> OptionsO

– Set snapping to “end”, “edge”, “vertex”, “point”, others

• Distance between vertexes (vertices)– fuzzy tolerance

– Streaming distance

• Level of zoom– Level of accuracy and precision can be affected

The MMU concept

• Minimum mapping unit

• Smallest entity mapped = resolution

• Similar to cell size for raster resolution

• Polygon width and length (vector)

30 m

poly15 m

poly

30 m

Gap

30 m

poly

20 m MMU example

Lo and Yeung 2001

3. Edge Matching

(from ArcGIS Help)

Spatial Adjustment toolbar

Edge Snapping

Geo-registration using common points instead

of control points (stretch-to-fit)Definition:

Spatial Adjustment toolbar

4. Rubber Sheeting

Geo-registration using common points instead

of control points (stretch-to-fit)Definition:

5. Topological Validation

• Follows edge matching step

• Purpose is to detect any errors in digitizing

– All polylines are snapped to each other

– No overshoots or undershoots

• In ArcCatalog create a feature dataset within

a geodatabase

• Define line topology rules

• Validate the polyline data with topology rules

Creating and validating a

geodatabase topology

• Done ArcCatalog in a feature dataset

• Create the feature dataset (right click on the

geodatabase and select New)

• Add the feature classes that will participate in

the topology (right click on the feature dataset

and select Import)

• Create the topology (right click on the feature

dataset and select New -> Topology)

• Enter the feature classes that will participate as

well as the rules, and validate.

6. Create polygons from polylines

• Feature conversion tools in ArcToolbox– Feature to Polygon

• Found in:

Data Management Tools>Features

– Others: • Feature to line

• Feature to point

• Polygon to line

• Creates polygons from line topology

Feature to Polygon

7. Attribute the Polygons in the

Database

• Area and perimeter geometry calculations

– This is automatic in geodatabase polygon

features classes (but not in shapefiles)

• Define additional fields

• Select (multiple) polygons and calculate

values into the fields

– Use the field calculator

Database Field types

• Short integer– “precision” (total width of a field)

• Long integer– “precision” (total width of a field)

• Floating point– “precision” (total width of a field– including decimal

places)

– “scale” (the number of decimal places in a floating point number)

• Text– “length” (total width of a field)

• Date

8. Database error checking

• Missing values in the DB

– Examine the polygon attribute table

• Incorrect values in the DB

• Groundtruthing

Polygon feature class

creation process --Summary

1) Georeferencing a scan or air photo

2) Digitizing polylines

3) Edge matching • merge or append the data

4) Rubber sheeting

5) Topological validation• checks for line errors

6) Create polygons from polylines

7) Attribute the polygons in the database

8) Attribute error checking

Editing in ArcMap

• Display the Editor toolbar

• Select the “target” layer in the toolbar

– You can edit from one folder at a time

• Select the “task” in the toolbar

• Edit toolbar menu

– Editing optionsO• set snapping tolerance

– SnappingO• Select layers for snapping (vertex, edge, end)