The idea for creating a model of a Vancouver city block for shadow analysis came from an article in the summer of 2010
addition of Arc News, “Virtual City Template Enables 3D City Modeling.”
The article was presenting the new 3D modeling capabilities of Arc10.
The new 3D capabilities allows for shadow analysis of
buildings. The article did not provide much more information but it
provided a source for further reading, on the ESRI website. From here we
downloaded a demo map and extrusion manual that would allow us to conduct a volumetric
shadows analysis. In order to conduct this analysis we had to download
the CreateSunPoints.py tool. This would allow us to create a light
projecting body in the sky. For this to run, we also needed to download
PyEphem. PyEphem is a series of python code that when given the
coordinates, date, and time of day, will create the exact location of
the sun at the desired date time and location. The
CreateSunPoints.py tool acts as the interface for PyEphem. This
analysis can only be run on ArcScene at the moment, however it can be
projected in ArcGlobe Once these downloads are complete there is a
three step model provided that walked us through the next steps. The
demo map that was supplied was of P
hiladelphia, Pennsylvania.
The first step was to take the
`Buildings’ multipatch layer and use
it for an input for the
CreateSunPoints tool. The tool also requires a sun distance. This
determines how visible the sun will appear on your display. It has a
combo box that requests the time zone the projection is in. We selected
the Eastern Seaboard, New York. It then asks for a start and end date
for you sun projection. We chose only to account for a single point in
time, however you could run it over several days if one wanted too. We
saved are output as Building_Sun and moved on to the next step in
the
model. hiladelphia, Pennsylvania. The next step involves the skyline tool. The skyline tool can be found in your 3D Analyst Toolbox under 3D Features. The sun points are fed to the Skyline tool as observer points and as ‘Input features’, we’ll use the buildings we want to calculate shadow silhouettes for. To tell the Skyline tool to create shadow silhouettes, you need to check the ‘Use Refraction’ box. We used the defaults for the remainder of the boxes. The output we named Building_silhouettes.
The Building_silhouettes are used as the input feature in the skyline barrier tool, the third step in the process. This tool can be found directly below the Skyline tool. We used the Buildings_Sun that we created earlier as the observer point input. We named the out Building _shadows and ran the model.
