Monday, March 31, 2008

Revit 2009 - Smart about shading surfaces

The Revit 2009 line of products offers some rather nice improvements in regard to the structure of the gbXML file, as well as in regard to how the geometry is translated into the same.
The first visible improvement starts with Energy Data entry within RAC 2009 Project Information options. The user will have the option to define the ground plane location and project phase as well as the “Sliver” tolerance, which specifies the tolerance for areas that will be considered sliver spaces.
But to me the most interesting one is the ability to specify whether the exported analytical model will contain "Shade" surfacesTypes enumerators or not. If the decision is made to export the model without Shade surfaces, the resulting gbXML file will represent pure space/volume analytical geometry, stripped of any intended or unintended "Shade" surfaces.

In the case that you really don’t care whether the addition of "Shade" surfaces will offset your results, go ahead and turn on the "Shading Surfaces" option, and voila, they are back whether you like them or not. This opens the possibility of manually merging the non "Shading Surfaces" model with only those shading surfaces that are welcome in your analysis, like eaves , overhangs, and various tectonic elements that will impact the insolation loads.
The following workflow describes one possible way of merging both gbXML files by using GBS’s VRML browser and a suitable XML editor like XML Marker.

Export two gbXML files: one with "Shade" surfaces turned off and one with "Shade" Surfaces turned on.
Submit the one with "Shade" surfaces to GBS and look at it in the VRML viewer. Examine the surfaces whose name contains “depx” as part of their description and this will help you identify those that you are willing to keep.

Once those surfaces are identified, in the XML editor open the file containing "Shade" surface, copy the entire surface(s) definition, and paste them by appending those after the last element definition in the gbXML file that does not contain any of the “ShadesurfaceType enumerators. Save the modified file and compare the results.

If you work with a relatively small building these results will not be noticeable, but as the scope increases and the complexity of the structure increases, as well as the need to switch from generic building elements to those that have real world thickness, the difference between these different Shading Surfaces options will become more evident.

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