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GIS and CAD (computer aided design)



GIS and CAD  
(computer aided design)

UT-Dallas  Briggs GISC 6382 Applied GIS



CAD and GIS 

GIS and CAD have similar data content but have:

  • Different fundamental philosophies
    • CAD sees the world as a cube
    • GIS sees world as a sphere
  • Different primary applications
    • Detailed construction design (larger scale)
    • Real world representation and modeling (smaller scale)
  • Different data models
    • As we shall see
  • Different editing environments
    • Editing is CAD��s speciality
    • But ArcGIS editing is becoming more ��CAD-like��


UT-Dallas  Briggs GISC 6382 Applied GIS




  • ESRI no longer trying to compete as a CAD vendor
    • ArcCAD product has been discontinued
  • Goal is now the integration of CAD data and GIS data via
    1. Common storage environment
      • data can be stored in SDE (using ArcSDE Client for CAD) for common access by both CAD and GIS users
    2. Use of CAD data in ArcGIS without the need to convert to GIS
      • Can be displayed
        • As CAD drawing layer: displays drawing file as it would be seen in CAD
        • As feature layers: which can be processed like GIS, but without conversion
    3. Bi-directional conversions between CAD and GIS data
      • Use ArcToolbox to convert CAD to GIS & GIS to CAD
        • ArcToolbox>Conversion Tools>To Geodatabase>Import from CAD
        • ArcToolbox>Conversion Tools>To CAD>Export to CAD
      • not necessarily transitive: cannot always reproduce the original CAD data after converting to GIS ��cos of inherent differences in CAD/GIS data models

UT-Dallas  Briggs GISC 6382 Applied GIS



How CAD Differs 

  • Lacks database environment
  • Lacks spatial analysis
  • Lacks topological information
    • connectivity, congruency and contiguity (adjacency)
  • Lacks layering within point, line and polygon classes
    • All line features (e.g. roads and streams) are in same layer
  • Features are not ��segmented��
    • E.g. Belt Line Rd all around Dallas is one feature
  • ��Cartographic�� information is often present in layers, undifferentiated from true geographic features
    • ��blowups,��  symbology,  legends, etc..
  • Limited support for real world positioning (map projections, etc.)

UT-Dallas  Briggs GISC 6382 Applied GIS



CAD files in ArcCatalog:   9.2  v. 9.1 

In ArcGIS 9.2, a CAD file is displayed in ArcCatalog as a  group layer with a ��triple box�� blue icon

Within this group there are:

    • multiple  feature layers containing  annotation, point, polygon, polyline (arc) line data, all with blue single box icons
      • These can be used for display, query, and  analysis as though they were regular, separate GIS layers
    • A single drawing file,which display all layers simultaneously, as they would appear to a CAD operator,
      • More akin to an ��image�� although it��s a vector file
      • Potentially useful as a background

You  can bring the layers (one, some or all), or the drawing file, or both into ArcMap, as desired.

ArcGIS 9.1 and earlier differs. The drawing file is shown as a second layer so you get two layers for every CAD file. 

9.1 and



UT-Dallas  Briggs GISC 6382 Applied GIS



A single CAD file can have up to 999 ��layers�� of vector data within its point, arc and polygon datasets. These can be separated into homogeneous GIS-type  layers by:

    • Accepting the ��CAD unique entity value�� symbology, which is the default in ArcGIS 9.2
    • Controlling display of drawing layer or feature layers via Properties/Drawing Layers (this is unique to CAD)
    • Separate feature layers (point, polyline, or polygon) into homogeneous GIS layers using the CAD ��layer�� variable, or other variables if appropriate
      • Via Properties/Symbology
      • Via Properties/Definition Query
    • You can  save the results as separate layers in TofC of ArcMap,  and as layer files to use in other ArcMap documents
  • Layers can be displayed, queried and used in many geoprocessing operations  in ArcToolbox as though they were regular GIS layers
    • However, there are exceptions e.g. can��t clip them or use as the clip layer
  • In all cases here you are processing the original CAD data, thus any edits made in CAD will be immediately available to the GIS user. This is the big advantage.

Using  CAD files in GIS

UT-Dallas  Briggs GISC 6382 Applied GIS



Converting CAD to GIS:    three ways

1. Use the standard Data/Export facility in ArcMAP or ArcCatalog

    Identify individual layers as per previous slide, then export as  separate shapefiles or gdb feature classes

    • This is by far the easiest conversion method
    • Generally, one CAD file produces multiple GIS feature classes

2. Use the Import from CAD tool in ArcToolbox

    Go to ArcToolbox>Conversion Tools>To Geodatabase>Import from CAD

    • Use this if you need access to ��fancy�� aspects of the CAD data
    • See When to Use the Import from CAD tool in ArcHelp

3. Use ArcInfo Workstation commands DXFARC and IGDSARC

Converting GIS to CAD:

    Go to ArcToolbox>Conversion Tools>To CAD>Export to CAD

    • Relatively complex issue
    • Other tools in the To CAD toolset are used to set up data appropriately prior to running Export to CAD tool
    • See ArcHelp for more detail

Converting  CAD files

UT-Dallas  Briggs GISC 6382 Applied GIS



Working together 

  • Engineers/designers make limited use of GIS when designing and building
    • However, the data they create can be very useful  for GIS
  • CAD provides multiple ways of creating data
    • Adoption of a set of ��CAD standards�� can greatly improve the usability of CAD data in GIS
    • Getting the CAD people to do  this requires diplomacy!
  • The ESRI document  Creating Compatible CAD Data for ArcGIS, October 2003, provides guidance.    Examples include
    • Use only one geometry type (e.g. line or  polygon) for a given feature
      • CAD people often intermix polygon and line features when drawing 
    • Use CAD blocks or cells to create point features rather than drawing them with lines 
    • Differentiate features (e.g. roads and railroads) in a consistent manner
      • use CAD layer variable, or a standard color, line style or width symbol
    • Snap features together using CAD snapping tools, especially for networks
    • Avoid splitting lines  to insert text or point symbols
    • many, many more!!!
  • If possible, use the CAD layer in GIS, rather than converting to GIS. Then, any new CAD edits can be captured immediately
    • If not, be sure to implement a process for update of GIS layers when CAD changes
      • For this, use a Modelbuilder Application so it can be repeated consistently!!!


UT-Dallas  Briggs GISC 6382 Applied GIS



Commonly encountered CAD file extensions 

.dxf   -     Autocad DXF (digital exchange format) arcdxf 

          also a pseudo standard for the exchange of CAD data

          (equivalent to a shapefile)

.dwg -     AutoCAD drawing file format

.dgn   -    Intergraph��s Interactive Graphics Design Software (IGDS) 

                and MicroStation Design format

UT-Dallas  Briggs GISC 6382 Applied GIS



Some Useful Reference Documents 

ESRI White Papers

  • Using CAD in ArcGIS,  June 2003
    • UsingCADinArcGISJ9059.pdf
    • This is a helpful overview
  • Creating Compatible CAD Data for ArcGIS, October 2003
    • Creating_Compatible_CAD_Data_for_ArcGIS.pdf
    • More detailed discussion of how to structure CAD data to maximize/simplify its use in GIS
  • CAD and the Geodatabase, July 2001
    • J8687_CAD-GIS_Geodatabase.pdf

Available from www.esri.com and also from http://wilbur.utdallas.edu/gisdata/g6382/Info_materials/


UT-Dallas  Briggs GISC 6382 Applied GIS

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