Integrating Administrative CAD Data, GIS and Google Earth
This tutorial takes a look at how the GSD's CAD floorplans -- maintained for adminstrative purposes, may be automatically transformed (every night if necessary) to display room and desk numbers, and desk/studio/student associations.
Georeferencing CAD Data
Seeing how this application is set up, we will see a couple of different means of georeferencing CAD data:
- A building Skin Model is brought in to ArcGIS from sketchup. In sketchup it is already georeferenced. This is accomplished with the Sketchup Plugin for ESRI ArcMap. At the time of this writing (May 2007) this plugin only works with Sketchup 5.
- The CAD drawings of the building that are used to maintain the room and desk numbers can be viewed directly in Acrmap.
- An auxiliary World File is created, to register the CAD file to the Building Skin (and the Massachusetts State Plane Coordinate System.) see the file 05f.wld in the sample dataset.
Processing CAD Data to Features
DWG and DXF files have a very limited structure for handling semantic infomration -- for example the relationship between room numbers and room polygons, for example. Nevertheless a person can create layers and annotations to store this information, and through a GIS workflow (which unfortunately has to be figured out for each CAD file!( this information can be put together. The following steps describe this process in detail. Or if you prefer, you can justrun the Cad to Shape model from the GundCAD toolbox -- See picture.
- Because ArcMap digests the CAD file into separate logical feature layers, we can use Select By Attributes the room polygons from the AnnotaPolygons Layer ("Layer" = 'U-SPAC-ROOM')
- We can also select points for the room numbers from the Annotation Layer Layer" = 'U-SPAC-RMNO' or "Layer" = 'DESKNUMBERS') and save these to a new points shape file.
- The next two steps are going to create new geometry. Thopugh our CAD data is georeferenced to the Massachusetts State Plane coordinate system, we can use ArcGIS to create the new geometry in the CRS that is needed by Google Earth (Decimal Degrees of Latitude and Longitude, assuming the The world Geodeitic Sheroid of 1984. This is acco,plished by setting the Output Coordinate System parameter of each wizard's Geoprocessing Environment
- So we use the Feature to Points (Data management->Features toolbox) to turn our selected points to a new points shape file.
- We then create a new polygon shape file integrating the polygon geometry and the room numbers points using the Feature to Polygon Tool.
- Next, we raise our room polygons to the right height, using thr Calculate Field Values tool to update Elevation Field for each polygon to 20 meters.
- Finally, we use the Shape to KML tool from Zonum Solutions to convert our room floor plan to KML. We use Sketchup to convert our buildng skin model to KML/Collada, and we can view them together in Google Earth!
The GIS resources and tools described in this document can be used without muck knowledge of GIS. If you are interested in how these resources and procedures were put together, you should take a look at some of the GIS user manuals found in the GSD's GIS manual, GIS User Manuals Page
- Using ArcMap for background on GIS data layers and attributes, and how to navigate in the ArcMap interface.
- Geoprocessing in ArcGIS Especially for background on setting the geoprocessing environment for Output Extent.
THe GSD Building Services Department maintains a set of CAD Drawings representing the rooms, studio carels and seating arrangements for Gund Hall -- the building that houses the GSD. Like most CAD data, these drawings are each in their own arbitrary coordinate systems, and the organization of the geometry is a bit haphazard -- as is typical with CAD databases not intended to be used with GIS. Nevertherless, we have been able to set up a process that can georeference each floorplan scrape the room numbers and floorplans and export them to google earth. The next version of this will allow departmental staff to outline the studio areas, so that each term the association between studio desks and studio courses.