The shapefiles for STK’s Urban Propagation capability must have polygon features to represent building footprints and an elevation attribute to represent elevations of the buildings. The specific requirements are:
- The shapefile type must be Polygon, PolygonM, PolygonZ, or PolygonZM (the MultiPatch type is not supported).
- Projection must be Geographic (also known as Lat-Lon).
- Horizontal data must be referenced to WGS84.
- Shapefiles must include an elevation attribute field with building elevations. You will need to know the attribute’s properties, in particular:
- Field name
- Units, either in feet or meters
- Vertical reference, either height above mean sea level (MSL) or height above terrain
The STK Urban Propagation model does not support UTM coordinate-based geometry shapefiles.
For information on verifying the validity of a shapefile, see Verifying Validity of Shapefile Using Global Mapper.
Understanding the shapefile
A shapefile is a set of three binary files and a *.prj file. The *.prj file is a text file that contains the shapefile metadata. The shapefile data format (binary data building geometry file) must be consistent with the metadata description in the *.prj file. STK may not be able to process the building geometry data if the data in all the files are not consistent. Converting the file data to a WGS-84 format and creating a metadata file may help to load the shapefile data into STK. STK will import building geometry data from files with the latitude/longitude format on the WGS-84 reference frame.
Polygon or PolygonM
This is the preferred shapefile type for use with Urban Propagation. This type uses X-Y geometry to capture the building footprints and it relies on the elevation attribute to extrude the buildings. Although this geometry is planar, it can drape over uneven terrain and correctly extrude buildings
PolygonZ and PolygonZM
These shapefile types may need some extra work compared to Polygon or PolygonM shapefiles. This type uses an X-Y-Z geometry to define the building footprints and it similarly relies on the elevation attribute to extrude the buildings. These shapefiles can be authored according to various conventions and you need to understand how they are defined.
The Z geometry introduces some complexity and it is important to understand how it is interpreted by Urban Propagation. For building elevations, the analysis engine relies on the elevation attribute alone and ignores the Z geometry values. In that sense, it is as if the file were a regular Polygon type. Graphically, however, the Z geometry is not ignored, so you may have a gap where the building is being analyzed and where it is being drawn in the 3D environment. To mimic how the Z geometry is ignored in the analysis, consider the following graphics workarounds:
- Go to 3D Graphics Details properties page and respecify the definitions for heights and bases of the buildings.
- Edit the shapefile and ensure that the Z geometry is universally set to zero. Keep the elevation attribute intact.
- Edit the shapefile and remove the Z geometry. This effectively converts the file from a PolygonZ type to a Polygon type. Keep the elevation attribute intact.
Verifying validity of shapefile using Global Mapper
If you have Global Mapper, do the following to verify whether or not your shapefile meets the requirements.
- Open the shapefile in Global Mapper.
- Click FEATURE INFO TOOL and click a feature in the map. The Attribute Column must have a field for building elevations. The elevation values can be in feet or meters; you need to know the unit in which the elevation values are specified.
- Click OPEN CONTROL CENTER, select your shapefile name, and click Metadata….
- AREA COUNT determines the number of polygons. It must be nonzero. You cannot determine whether or not the shapefile type is MultiPatch with Global Mapper. If it is, you will get a warning with the Urban Propagation Extension.
- PROJ_DESC must be either "Geographic (Lat/Lon) / WGS84 / arc degrees" or "UTM / WGS84 / meters".
