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Exporting Parametric Geometry with the Rhino/Grasshopper Plugin
Exporting Parametric Geometry with the Rhino/Grasshopper Plugin

FAQ: Parametric and Curved Geometry for cove.tool workflow

Written by Patrick Chopson
Updated over a week ago

If you have highly intricate parametric geometry in Rhino, speed up your simulation by using the Mesh command in Rhino first to extract the mesh triangles. Follow these steps to get your geometry simplified and exported. The fewer the triangles the faster it will run. For an accurate simulation, thousands triangles are not necessary.

Let's Begin

The procedure to reduce your model's triangle count occurs before launching grasshopper. Start simplifying the model's geometry after you have filtered the geometry into the various building components like walls, windows, roofs, floors, etc.

1. Select the Surfaces to Simplify
Depending on how much of your building is complex, you may only need to simplify geometry that contains non-single surface geometries. Simplifying one layer at a time may significantly expedite the reduction process. This tutorial will show the process with the layer of the exterior wall.

2. Run the ExtactAnalysisMesh command
Running this command generates a mesh which is the approximation of your geometry. If your objects are already meshed then move to the next step. Once you run this command the original surface will remain selected in a view, delete the original geometry, or re-layer elsewhere to not have operation occur to undesired objects.

3. Next run the Mesh command.
The Mesh command will launch a dialog window. Users have the option to reduce the polygon count using either the # of polygons or to reduce by a percentage. We recommend you use the percent option, and enter a value of 80% or greater. To make the model run faster in the analysis you can be as aggressive as you are comfortable with. The more simplified the model the faster it will run. After reducing the polygon count, the new mesh will have a fraction of the polygons once displayed.

4. Convert mesh(es) back to planes with the MeshToNurb command
Converting the mesh(es) back to planar geometry will make it compatible geometry for the plugin process. Once you run this command the original mesh will remain selected in a view, delete the geometry so that only planar geometry remains.

5. Type Explode to convert all objects to single-surface geometry
Objects after the mesh reduction process will remain as poly-surfaces until un-joined with the explode command. Leaving poly-surfaces, meshes, or other non-single surface geometry in view will crash the plugin or will not be detected by the plugin.

6. Repeat the process for the other complex geometry layers.
Go through the other layers to convert and simply your building geometry to simple single-surface objects.

7. Once all geometry has been simplified
Wire the geometry back in the same way as before. Now you should get super-fast analysis back every single time. There is a way to do this with grasshopper but this one will be the fastest because you can check the results as you go and ensure the fidelity of the model is not being negatively affected.

Why do this?
When geometry is selected for plugins, three steps are occurring simultaneously. First, the plugin is creating a list of all the planes in the selection. Once it has a list is creates two columns for each building category (windows, roofs, etc.): one for the object's surface area, another with the list of each plane's construction vectors and their coordinate positioning in space. The final file size is typically less than 10 MB, even for our largest projects.

Files that were parametrically designed, or have a double-curved surface have a high-triangle count. when simplified to single surface planes (steps 1 of the export tutorial). Files with similar modeling practices can generate a file size in excess of 300 MB. That is because each plane is recorded and every surface has dozens to hundreds of construction vectors. Thus the issue that is causing a failed export is project complexity and not Project size. Therefore the steps in this article to get your model on track for export is to reduce the triangle count but still have the design's integrity evident when recreated in cove.tool.