# Physical Modeling 6.2 [topography method 2]

## “Generating a Topographic Model from Rhino (Option 2)”

1. Begin with a NURBS surface that represents the desired topography that you would like to build a physical model to represent.
2. Follow Rhino Tutorial 5.20 to create a series of vertical contour lines that divide the surface into even intervals of desired width. Your “direction perpendicular to the contour lines” should be the x-axis. Your intervals should be based on the desired grid for your final topography (for example if your final scale is 1/16” = 1’ and you want your grid to be 1” square, use 16’ as your interval in this step).[premium content]
3. Now select all of the curves you created in step 2.
4. Use the rebuild command to make each curve have the same number of control points. You can use your best judgement here for the point count (too few will lead to a simplified surface, to many will add unnecessary detail). Also, set the degree to 1.
5. Now select pairs of curves created in step 4 and loft them together. You need to do these separately so that they will unroll properly in the next step.[premium content]
6. Select each lofted surface. Use the unrollsrf command to unroll each surface. Please ensure ‘Explode=No’ in the command line. Also, keep the unrolled surfaces in order so that you can assemble them correctly later. You may wish to turn labels on, though this can add confusion.
7. Now, turn off the layer containing the unrolled surfaces and the original surfaces (if they are not on their own layer, put them on a new layer and turn them off). You will work with just the curves from step 4.
8. Use the vertical plane tool to draw a surface the width of one of these contours, but taller than the contour (see example below).[premium content]
9. Use the array command with the same spacing you used for your original contours (step 2) to create a series of vertical planes, one at each of your contours.[premium content]
10. Now use the trim command to trim off the top of the vertical plane (where it extends above the contour. Leave the bottom of the plane intact as this will form the base for your topography.[premium content]
11. Select each surface and use the dupborder command to create a polyline around each of the resulting surfaces. These fins will form the base for your unrolled surfaces created in step 6.
12. Use the rotate3d command to rotate each polyline flat and arrange the fins in an order you can remember.
13. Turn on the unrolled surfaces and use the scale command to scale the surfaces and the polylines created in step 12 from full scale to your model scale.
14. Arrange both the fins and the unrolled surfaces on a 12” x 24” sheet(s) for the laser cutter and, with all objects selected, use File>Export Selected… to create a 2004 .dwg file (for laser cutting).
15. Follow Physical Modeling 6.3 [laser cutting from AutoCAD] / Physical Modeling 6.4 [laser cutting from Illustrator] to cut your pieces. You will need to assign colors either in Rhincoeros or AutoCAD/Illustrator with pure red as “cuts” and pure blue as “engraves.”
• Note: Depending on the thickness of the material you are cutting, you may wish to cut blocks to fit in between each fin and hold the base stable as you glue all the pieces together.