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Tutorial:
SketchUp Foam Core Model

SketchUp is the sketch-based 3D design program from @Last Software. SketchUp provides a means of creating a terrain as a collection of slabs referred to as a foam core model. You can convert that into a contiguous set of planar surfaces as follows. (This tutorial requires that you have SketchUp.)

Export from SketchUp

• While still in SketchUp, open or create a drawing which consists of a foam core model. A few samples are provided; in this tutorial, you should open the file contour-example.skp.

• Choose File > Export > 3D Model..., and export in AutoCAD 2000 DXF format. Click the Options button and choose to export only the edges. Set the filename to "contour-example SU to SMT.dxf". Click the Export button.

Import into SimuTerra

• Start up or switch to SimuTerra.

• If you don't have an empty 2D window in front, choose File > New.

• Choose File > Import DXF.

• Find the DXF file which you just exported, or the sample file contour-example SU to SMT.dxf, and click Open.

• Read the results which are displayed, and click OK.

Note that data appears in a 2D view, and it is all selected.

• Choose Window > New Window (not File > New) in order to create a new window of the same document.

• Choose View > Display in 3D so that the new window will display its contents in 3D.

If you did this in a different order, you may need to choose View > Fit to Window in order to see the contents in the 3D view.

• Drag the mouse around in the 3D view so as to see what the DXF file consisted of.

Note that for each "contour line" there are two series of edges, one higher and one lower, connected by vertical lines. And there are edges around the perimeter as well. All of this can lead to confusion in a terrain modeling program, though SimuTerra is customized to handle this situation.

Create a DTM

• To create a DTM from foam core edges, ensure that the data is still selected. This would be apparent only in a 2D view, so you may want to move the 3D window to the side, and choose Edit > Select All.

• Choose DTM > "Create DTM from SketchUp Foam Core Edges".

Note that a new surface is draped over the imported data.

Export DXF

• Choose File > Export DXF....

A dialog will appear, DXF Export Entity Options. Choose only one of the items. The second one, "Square grid as polyface mesh", may be more appropriate. Click the OK button.

• Give the file a name, such as contour-example SMT squares out.dxf, and indicate where to place it. In most cases you will want the file name to end with the default dxf suffix. Click the Save button.

Import into SketchUp

• Switch back to SketchUp, and have the original file contour-example.skp in the frontmost window.

• Choose File > Insert > DWG/DXF... so as to open a dialog.

• Select the file which you just exported from SimuTerra, and click the Open button.

Note that the results dialog indicates that one entity was imported, a polyface mesh.

• Click the OK button in the results dialog.

Note that the surface which you imported is draped over the original SketchUp model. On horizontal surfaces you'll see some of each of the original data and the imported data, because they are coplanar.

Also note that the imported polyface mesh is understood by SketchUp. It consists of a contiguous set of squares, where each square is divided into two triangles by an invisible diagonal. This forces all polygons to be planar.

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