1. Differences between CAD and GIS data structures
CAD (DXF, DWG, DGN)
GIS (Shape, TAB, GeoBase)
Supportin engineering drawing
Querying, analyzing spatial data
Several element types
Point, polyline, polygon, (text)
One file, several layer (foil)
On layer, some files
Spaghetti data model
Topologic data model
Stores display attributes too
Stores geometric data only
Attributes are optional
Attributes are always considered 3D
2D, 2.5D
Projection

2. CAD Text CAD objects Line Circle, arc, ellipse, elliptical arc
Polyline, polygon, spline
Text
3D object (cube, sphere, cone, etc.)
Dimesioning objects
etc.
Text
CAD

3. GIS objects
Point/node
Polyline (arc)
Polygon
GIS

4. Vector and raster data representation
Vectors
Rasters
Smaller data sets
Huge data sets
Unlimited resolution
Limited resolution
Complex data structure
Simple data structure
Hybrid model

5. Layer and object data model
Layers, horizontal grouping
Objects, vertical grouping
Building object 12
Building
Terace
House
number
Parcels
Buildings
Water
Trees
Layers
Parcel object
1234/1
Parcel
subparcel
Pacel ID

6. Graphical and attribute data
GIS 1:1
1 layer – 1 table
1 object – 1 record
CAD n:m
1 drawing – many table
1 object – many record
1 record – many object
Graphic database
Relational database 12
x1,y1;x2,y2;x3,y3;x4,y4
/ L4
Graphic data + identifier
Attribute data + identifier

7. Data Exchange Formats
Industrial standards, attached to specific software
CAD
GIS
MIF/MID
Shape
DXF
INFOCAM sequential
E00 …
DGN
DWG
Independent standards
National standards
XML
ATKIS
SDTS … …
SVG
GML
DIGEST …
SDTS – Spatial Data Transfer Standard
DIGEST – DIgital Geographic information Exchange STandard

8. DXF format SECTION 2 HEADER … ENDSEC TABLES BLOCKS ENTITIES EOF TABLE
SECTION 2
HEADER …
ENDSEC
TABLES
BLOCKS
ENTITIES
EOF
DXF format
TABLE 2
LAYER 70 1
0 layer name
0 visible 62
7 color 6
CONTINUOUS linetype
ENDTAB
LINE 5 2B 8
0 layer 10
10.0 x1 20
30.0 y1 30 z1 11
150.0 x2 21
80.0 y2 31
0.0 z2

9. MIF/MID format Version 300 Charset "WindowsLatin2" Delimiter ","
CoordSys NonEarth Units "m" Bounds (-1390, -470) (1550, 580) projection
Columns 1
ID Integer structure of database table
Data
Line
Pen (1,2, )

10. Shape format Binary format .shp – co-ordinates of elements,
all elements must have the same type, point, polyline or polygon
.dbf – dBase database table
.shx – minimal boundary rectangle (MBR)

11. XML format
<?xml version="1.0"?> <matrix> <comment>This is a matrix</comment> <r> <c>1.2</c> <c>3.5</c> <c>-1.2</c> </r> <r> <c>2.4</c> <c>1.9</c> <c>11.8</c> </r> <r> <c type=int>4</c><c>6.5</c> <c>-0.6</c> </r> </matrix>
<?xml version=„1.0”?> <!DOCTYPE matrix [ <!ELEMENT matrix (r+, comment?)> <!ELEMENT r(c+)> <!ELEMENT c (#CDATA)> <!ELEMENT comment (#CDATA)> <!ATTLIST c type (int|real) #IMPLIED> ]>
dtd – document template definition
schema – schema definition
xml parser (e.g. xerces)

12. SVG format <?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG //EN„
"
<svg width="600" height="300">
<g>
<line style="stroke:black;" x1="10" y1="30" x2="150" y2="80"/>
</g>
</svg>

13. KML format
<?xml version="1.0" encoding="UTF-8"?> <kml xmlns="
<Placemark> <name>Simple placemark</name> <description>Attached to the ground.</description> <Point> <coordinates> ,
,0</coordinates> </Point> </Placemark>
</kml>

14. DAT format MSZ 7772 Hungarian standard 1996
Rigid table structures and objects
For land cadastre data
DAT sample T_PONT* 1* * **7** 2* * **7** 3* * **7** … T_HATARVONAL* 1*1*4*3*0** 1*2*3*1*0** 1*3*1*2*0**
ATKIS in Germany
SDTS in the US

15. Useful links
ioc.unesco.org/oceanteacher/resourcekit/M3/Formats/ Integrated/ DXF/ASCII DXF File Format.htm

16. Creation of digital maps
Secondary data sources
Primary data sources
Digitizing
Numeric data
Geo-
reference
Scanning
Table
digitizing
Observations
fieldbooks
Automatic
vectorization
Manual
vectorization
Numeric data input,
constructing
Digital raster map
Digital vector map

17. Raster to vector conversion (R2V)3 2 1 4 P 5 6 7
Pixel N neighborhoods, even – edge neighbors
Steps of vectorization
Found the border,
One of the n neighbors has background color
Object thinning, until multiple pixels left only
(maximum 2 pixels wide)
Multiple pixels, more than ones in the border
Semi-automatic method
Raster snap
Optical Character Recognition (OCR)

18. Topology Continuity and neighboring information for map objects
They are invariant from the chosen co-ordinate system
They make analyzis functions faster, e.g. shortest path 1 5 2 4 7 6 3
Graphic objects
Reference ő
point (tic)
polyline
centroid (label)
polygon tó
annotation
node 8 9 10 11 12 13 14 15 16 -
Centroid id
Polyline id
Node id

19. Drawing cleaning Aims – find and correct topological errors
Automatic solution, tolerance
Drawing error
Explanation 1.
duplicate objects
Objects that share the same start and end points
Delete one of them 2.
short objects
Objects shorter than the spaoecified tolerance
Erase them 3.
undershoots
Objects that come within the specified tolerance
radius of each other, but do not meet 4.
overshoots
Object overpath another object shorter than the
Specified tolerance
Break crossing objects and erase overshoot part 5.
crossing objects
Objects cross each other with no node at crossing 6.
clustered nodes
Any nodes within the specified tolerance distance
Snap them to the centermost node 7.
pseudo nodes
Any node shared by only two objects
Dissolve the node and join the two objects 8.
dangling objects
Objects with at least one endpoint that is not shared
by another object. Erase the object
Break crossing objects and create node at crossing