Multipatch footprint of Sun Shadow Volume in ArcScene (removal of below ground shadows)

Question

I am new to using ArcScene and encountered a problem in my analysis. I want to calculate shadows in the city center of Utrecht on different times and days. Subsequently I want to transform these shades to polygons that represent the amount of shade on streetlevel. I am using the tools Sun Shadow Volume and Multipatch Footprint.

I extruded a layer with buildings (with heights in the attribute table) on a TIN with the baseheights of Utrecht, which is almost flat (image 1). Subsequently I ran the Sun Shadow Volume tool, which seems to work fine. However, the resulting shades cut through the baselayer (image 2). When I want to transform them to footprints, I get the footprints at the lowest point, instead of at baseheight level (image 3).

Does anybody know whether I can change the settings in Sun Shadow Volume tool somehow? Or in the Multipatch Footprint tool? Or did I already do something wrong with the extrusion?

Answer 1

I also encountered this problem (shadows appearing below the ground) and it took me a while to figure out a workaround (I suspect that the problem exists because the tools are not yet used very much - I had to figure this out on my own!) You basically need to select only the above ground shadows and delete the rest.

My (not very eloquent) workaround was the following:

• Create a new polygon that covers the extent of your study area ("clip.shp")
• Add a new field (type = double) and assign a value of say '100' (this value is to be used for an extrusion so make sure that you have no features higher than this in your study area)
• Convert the polygon ("clip.shp") to a raster (Conversion Tools > To Raster > Polygon to Raster), perhaps named "clip_dem"
• Convert this raster to a TIN (3D Analyst > Conversion > From Raster > Raster to TIN), perhaps named "clip_dem_tin"
• Use Extrude Between (3D Analyst > Triangulated Surface > Extrude Between) to extrude a TIN between the surface DEM and the sky. Where your first Input TIN is the DEM for your study area, the second Input TIN is the clipped/coverted TIN ("clip_dem_tin") and the Input Feature Class is your clipped study area extent polygon ("clip.shp")
• Then use Intersect 3D (3D Analyst > 3D Features > Intersect 3D) to create an intersected selection between the extruded TIN and your shadows to remove the below ground shadows. Note: I found that this process crashed quite frequently with large shadow model files (i.e. using multiple, close, time points - use a smaller file or subset to test this on first).

You're essentially making a big 3D block from the ground (with your DEM as its base) up into the sky and using that to select (intersect) the shadows that you want to keep.