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Preparing Rhino projects for the Grasshopper Plugin
Preparing Rhino projects for the Grasshopper Plugin

How to make sure your file will export from Rhino/Grasshoper.

Patrick Chopson avatar
Written by Patrick Chopson
Updated over a week ago

Make the export process as fast and freeze-free as possible with these Rhino model preparation steps.

30-second summary

Make sure your final stage model is only single surface objects that are not locked, grouped, a block, or in any other way connected to solid or combined with other geometry. Units must be in Feet. Only geometry on cove.tool layers will be referenced. Delete all bad objects and purge unused file elements. Ensure all surfaces are facing the correct direction with the front-face facing outward or upward. All geometry should be above the XY plane, and only geometry above ground should be exported.

Detailed Preparation Steps

1. Unhide, Unlock, and Locate your Rhino project near the Origin Point
Open your project. Make sure all your building geometry is un-hidden and unlocked by typing "Unhide" and "Unlock" in the command bar. Many processes will happen in this file. You may prefer to work on a copy of the primary model, but it is not necessary. Next, make sure your model is located near the Rhino origin axis (coordinates: 0,0,0). By placing your geometry here, it will ensure your building will accurately display once inside cove.tool.

2. Set Units to FeetThe grasshopper script requires geometry to be in Feet to display accurately in cove.tool. If your project is set to SI: Meters, that will remain the case after the daylight page. You can change model units by typing "units" in the command bar and hit enter. The "Document Properties" window will open, select "Feet" in the "Model units" dropdown list. Click yes when prompted to scale your model. Check the project scale by measuring the known length of your building.

3. Move all geometry to appropriately named layers
The plugin process is expedited by good layer management with the correct building geometry assigned to the correctly labeled layers assigned for each cove.tool export category. Categories include Floors, Roofs, Windows, Exterior Walls, Interior Walls, Skylights, and Shading Devices. The latest grasshopper plugin includes a "make cove.tool layers" button to automate this process, which makes layers for each building type assigned to the cove.tool project being referenced. Make sure all of the objects have been sent to their correct layer. A misplaced object can be normally swapped between layers, so make sure this is done before exporting your geometry to cove.tool. Misplaced objects are the #1 cause of inaccuracy in the plugin.

4. Explode, Un-group, and Delete all non-single-surface objects in your file

The grasshopper plugin will only accept single-surface objects. To check if your geometry is a single surface, highlight your project and type explode. This command may need to be repeated until objects cannot be simplified any further. The geometry categories below will need to be simplified with the following checks.

  • Grouped Geometry - Select blocks with command "SelGroup" and type "ungroup" and "explode" in the command bar until geometry has been simplified.

  • Blocks - Select blocks with command "SelBlockInstance" and type "explode" in the command bar until geometry has been simplified. Also, open the "BlockManager" and delete all contents to eliminate all block geometry.

  • Curves (Lines) - Select curves in a project with command "SelCrv" and delete, line geometry is undesired.

  • Polysurfaces - Select blocks with command "SelPolySrf" and type "explode" in the command bar until geometry has been simplified.

Note: If you modeled your building geometry with thickness and have six-surface polygons, that may cause severe model clean-up. Re-massing the project may be a faster resolution.

5. Purge File of Bad Geometry Bad Geometry is the number one cause of crashing grasshopper scripts. Luckily in Rhino, there are three helpful commands to eliminate bad geometry.

  • Purge (_Purge) - "Purge" command will search the entire Rhino File for unused and problematic model elements. Click enter twice to eliminate all purge-uncovered objects.

  • Select Duplicates (SelDup) - This command will find all identical objects which occupy the same 3D Space as an existing object. Delete all duplicated objects.

  • Select Bad Objects (SelBadObjects) - Bad objects are objects in Rhino that were brought over from a different platform and are struggling to display correctly and thus will not be able to export accurately with the Grasshopper Plugin. The solution is to rebuild these objects. One recommended method to remake a bad object is listed below.

  • Select one bad object at a time. Trace the bad object with command "Silhouette." While the traced curves are highlighted, type command "join" to join all curves, which will convert them to closed-curves. Convert the closed curve into a single surface with command "Patch." A window will pop up, in Surface U spans, and V spans change the "10" value to a "1", then click ok. Delete the bad object and lines, and you should now have a compatible single-surface object. If the object had openings, i.e. window punches, then the command "Silhouette" will have to generate multiple closed curves. Select only the most outer profile line of the object then type command "Patch" to convert it to a single-surface object. Then select the remainder of the trace outlines and then type command "trim" and click the area at the center of the outlines to trim the surface and create surface openings.

6. Check for flipped-face geometry
The cove.tool grasshopper plugin uses a property-tag front-face/back-face of each plane to determine the cardinal orientation of each surface. For Example, a surface's area will be filtered into the category of the direction that its front-face is facing (for reference, this is the same tag/property is used to apply materials on the surface). If area categories look incorrect, check your project for inverse-facing surfaces.

  • To check, use the back-face settings in "Properties>Rhino Options>View>Display Mode>Shaded - Back-face Settings" to set a 'single color for all the back-faces' (see image below). Surfaces facing the wrong direction [outwards] will appear in the back-face color.

  • To correct the orientation surfaces can be flipped in Rhino with the command "Flip" (second image).

It is critical to have all building envelop geometry displaying front-facing surfaces outwards, and all horizontal plane geometry have their front planes facing upwards. This step ensures all of your building components are imported with accurate cardinal directions, i.e. that your building geometry falls into the correct orientation (N, NE, E, SE, S, SW, W, NW). Once everything is correctly oriented, you are ready to export your building geometry.

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