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Differences between CAD and GIS data structures CAD (DXF, DWG, DGN)GIS (Shape, TAB, GeoBase) Several element typesPoint, polyline, polygon, (text) One.

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Presentation on theme: "Differences between CAD and GIS data structures CAD (DXF, DWG, DGN)GIS (Shape, TAB, GeoBase) Several element typesPoint, polyline, polygon, (text) One."— Presentation transcript:

1 Differences between CAD and GIS data structures CAD (DXF, DWG, DGN)GIS (Shape, TAB, GeoBase) Several element typesPoint, polyline, polygon, (text) One file, several layer (foil)On layer, some files Spaghetti data modelTopologic data model Stores display attributes tooStores geometric data only Supportin engineering drawingQuerying, analyzing spatial data Attributes are optionalAttributes are always considered 3D2D, 2.5D Projection

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

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

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

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

6 Graphic data + identifier Attribute data + identifier 12 x1,y1;x2,y2;x3,y3;x4,y4 12 4563/2 L4 Relational databaseGraphic database 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

7 Data Exchange Formats DXF MIF/MID ATKIS E00 Shape INFOCAM sequential DGN DWG SDTS XML SVGGML Industrial standards, attached to specific software National standardsIndependent standards CADGIS … … … … SDTS – Spatial Data Transfer Standard DIGEST DIGEST – DIgital Geographic information Exchange STandard

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

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 9.9999994 29.9999998 150.0000006 80.0000002 Pen (1,2,16711680)

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 This is a matrix 1.2 3.5 -1.2 2.4 1.9 11.8 4 6.5 -0.6 dtd – document template definition schema – schema definition xml parser (e.g. xerces) ]>

12 SVG format

13 KML format Simple placemark Attached to the ground. -122.0822035425683, 37.42228990140251,0

14 DAT format DAT sample T_PONT* 1*242176.480*646926.000**7** 2*242166.050*646901.500**7** 3*242166.050*646933.190**7** … T_HATARVONAL* 1*1*4*3*0** 1*2*3*1*0** 1*3*1*2*0** MSZ 7772 Hungarian standard 1996 Rigid table structures and objects For land cadastre data ATKIS in Germany SDTS in the US

15 Useful links ioc.unesco.org/oceanteacher/resourcekit/M3/Formats/ Integrated/ DXF/ASCII DXF File Format.htm http://www.opendwg.org http://www.bentley.com/opendgn/ http://www.directionsmag.com/mapinfo-l/mif/AppJ.pdf http://www.w3.org/TR/2000/REC-xml-20001006 http://www.classes.cs.uchicago.edu/archive/2003/fall/23700/docs/handout-03.pdf http://www.svgopen.org/abstracts/de_vries__gml_and_svg.html http://www.w3.org/TR/SVG/ http://www.agt.bme.hu/tutor_h/presentationhu/0h.svg

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

17 Raster to vector conversion (R2V) 321 4P0 567 Pixel N neighborhoods, even – edge neighbors Steps of vectorization Found the border, One of the n neighbors has background color Multiple pixels, more than ones in the border Object thinning, until multiple pixels left only (maximum 2 pixels wide) Semi-automatic method Raster snap Optical Character Recognition (OCR)

18 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 Topology

19 Aims – find and correct topological errors Automatic solution, tolerance Drawing cleaning Break crossing objects and create node at crossing


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