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Differences between CAD and GIS data structures

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Presentation on theme: "Differences between CAD and GIS data structures"— Presentation transcript:

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

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„ " /DTD/svg10.dtd"> <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 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 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

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