Storing GIS information in AutoCAD drawings

If you’ve ever tried to use AutoCAD xdata to store feature attributes in a DWG file you might be interested to know about the enhancements made to the Export-to-CAD tool in 9.3. In ArcGIS 9.3 storing GIS information in an AutoCAD drawing and the ability to read this data in ArcGIS Desktop is now automated.

For each feature class used as input, the Export-to-CAD tool will automatically:

  • Embed the feature class definition as a non-graphic entry in the DWG file.
  • Create a layer with a name that matches the feature class name.
  • Write the features to the matching CAD layer name.
  • Attach the corresponding ArcGIS feature attributes to each CAD entity.
  • And embed the coordinate system information as a non-graphic entry in the DWG file.

Both ArcGIS 9.3 and ArcGIS for AutoCAD Build 200 read and write this data out of the box. This makes round-trip data exchanges between ArcGIS Desktop and AutoCAD a straightforward and uncomplicated task.

Behind the scenes

Behind the scenes the information is stored as AutoCAD xrecords and organized into a framework of AutoCAD object dictionaries that is defined by the ESRI “Mapping Specification for CAD”.  As a result, there is no longer a need to burden workflows with complex xdata tasks. This new format stores ArcGIS information in the drawing’s Named Object Dictionary similar to other native AutoCAD data tools such as Plot Styles or Groups. This means your GIS data will not interfere with standard AutoCAD entities or commands yet remain accessible to ArcGIS or ArcGIS for AutoCAD.

Using the Export-to-CAD Tool

If you have an ArcView license or higher, the Export-to-CAD tool can be found in the ArcToolbox under Conversion Tools > To CAD > Export to CAD

Figure 1:

 

A simple use of the tool requires four steps (Figure 2). For simplicity this example does not use a seed file:

  • Enter or drag-and-drop the input features into the dialog.
  • Select the DWG output format.
  • Verify or enter the output filename.
  • Run the tool.

Figure 2:

The results

Viewing the results in the Catalog tree, the CAD dataset now includes an additional type of CAD feature class (Figure 3). In addition to the usual suspects, the dataset also contains uniquely named feature classes that correspond to the feature classes from the source geodatabase. For example Parcels.

Figure 3:

 

The contents of these feature classes are derived from their default parent CAD feature classes, Point, Line, Polygon, etc. This means, as in previous releases of ArcGIS, the default feature classes continue to maintain all CAD entities organized by type but these new feature classes only contain the CAD entities that belong to a particular feature class. In ArcMap this gives you the option of working with all or subsets of CAD data. For common workflows this can save you time from having to build specialized query definitions to accomplish the same result.

Attribute values

Another important distinction between the two types of CAD feature classes is feature attributes. As in previous releases of ArcGIS, the default CAD feature classes continue to be absent of attribute data. However, these new feature classes contain the attribute data that was present in the feature attributes table at the time the data was exported.

If you add this CAD data in ArcMap and use the Identify tool and scroll to the bottom of the field list, notice the feature attributes that come across from the feature classes in the sample geodatabase Montgomery.gdb (Figure 4). In this example the feature belongs to the Parcels feature class. In addition to the CAD property fields, the feature attribute field PARCEL_ID has a value of 9956.

Figure 4:

 

Summary

Beginning with ArcGIS 9.3, the Export-To-CAD tool now offers an alternative to using xdata or block inserts for storing GIS information. The benefit of this data persisting in an AutoCAD drawing is the ability to streamline workflows that routinely move data between AutoCAD and ArcGIS. Using ArcGIS for AutoCAD you can take this information and work with it, edit it, and add to it in a GIS context that mirrors your organization’s GIS data standards. This data can then be used as input to ArcGIS geoprocessing tools to update specific feature classes in your geodatabase – including attribute data.

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2 Comments

  1. sblgeomatic says:

    Nice post.thanks for sharing..

  2. palace says:

    Does ESRI have any info on how to access the embedded GIS attribute data from the Autodesk end? My users/clients don’t want to have to install the ArcGIS for AutoCAD plug-in.