Preparing the Ground Surface for Physical Site Modeling


Site Model - 7-bounding box.png

In order to prepare a digital model to be turned into a physical site model, we will "box out" the ground surface by creating side walls and a bottom surface so that it becomes a solid object instead of a floating plane. Additionally, we must fill in all of the holes where the building footprints are and join everything together into a closed polysurface.
Uses Tool(s) Rhinoceros

This workflow uses this Rhino model of Potrero Hill:

Re-Build the Ground Surface

Turn off the Fences layers, leaving just the Buildings, Sidewalks, Roads , and Backyards layers on. We need to create a base plan that include both all the surfaces layers and the ground floor of the buidlings. To do this, select all the objects in the Building layer and CopyObjectsToLayer in a new layer. Save the original Building layer for later.

To make this process easier, Explode all the building polysurfaces. Delete all of the rooftops and use the sidewalks and backyards to trim down the surfaces to meet each other. This process will take some time and some areas will be more difficult to trim than others.

Elements to consider:

  • How far down do you want each building object to be placed in the ground surface?
  • In the area for your design - do you want to allow space for more underground objects?
  • Will the site buildings be built separately or laminated together?

Site Model - 5-creating building footprints.png Once this process is finished, your ground surface should consist of building bottoms, the sidewalks, roads and in-between landscape pieces.

Box Out the Ground Surface

First, copy all of the ground surface elements created in the last step and copy them to a new layer titled "Ground". Join them all together so they are now one polysurface. Note: If the objects cannot join to one polysurface, this will require some cleanup later on when producing cut files. Try to get as close to one polysurface as possible by patching up holes.

Create a base rectangle from the lowest corner of the model to the extents of the base. This should be flat along the XY plane. Right now it's touching the lowest corner. In this case, we want the lowest edge of the ground surface to be sitting 1" above the bottom of the physical model. In perspective view, Move this rectangle down 1" using the Vertical option in the command line.

Then create the sides of this base. Explode this rectangle . Use the ExtrudeCrv command and select one of the outlines of the bottom rectangle. Extrude up to the highest point along that edge. Then use the interior polysurface of the ground to Trim the extruded edge.

If have any issues with trimming, use the Intersect command to find out where the polyline is not joined.

Create the bottom of the base by creating a PlanarSrf with the bottom edges of the base. This should be the same as the original rectangle created in the beginning of this step.

Closed Polysurface

Now select all of the surfaces that will make up the ground surface of the model. This includes the Backyards, Sidewalks, Roads, Ground Fill, and Sidewalks layers. Join these layers together to form a closed polysurface. To confirm that the polysurface is closed, click Details in the Properties panel, or simply type What in the command line. The resulting dialog box will tell you if the polysurface is open or closed.

Naked Edges

If the polysurface is open, use the ShowEdges command to identify any naked edges. A naked edge exists when the edge of one surface does not cleanly meet another surface edge. Essentially, a naked edge is a hole that prevent a polysurface from being watertight. After identifying any naked edges, use appropriate surface modeling commands to edit those highlighted edges until they meet cleanly and the polysurface is closed.