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Intersect Feature creates Subsurfaces/Windows/Skylights

asked 2015-01-12 20:13:51 -0600

updated 2020-01-26 11:51:03 -0600

I've run into an interesting problem which I believe to be a bug or flaw (possibly a failure to identify a use case) in the "Intersect" feature in the Surface Matching window of the Openstudio Plugin for SketchUp. It happens in a very specific case, but it is reproducible. To demonstrate i will build a two story building with two spaces per floor.

here is the first floor built image description

here is the second floor built image description

Then, the Intersect in Entire Model button is pressed. Below is the space with the issue selected image description

When we isolate that space and look underneath to see if the intersection worked, we see that instead of the surface being broken up into two surfaces, a subsurface is added which by default is rendered as a skylight. This is because the surface break starts from and ends at the same edge of the surface. image description

If the surface break is attempted manually, the same issue appears.

I understand that its uncommon for the floor of a room to be divided in such a way, but it must happen sometimes. Is there a way to convert the subsurface to a separate surface? otherwise, modeling the building described here is impossible as far as I can tell.

Any thoughts?

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answered 2015-01-12 20:41:26 -0600

I'd be interested in hearing from the developers regarding why this occurs, but a solution I've found is to subdivide the floor surface so that the 'subsurface' is not surrounded by a single larger surface by more than two edges:

image description

You end up with more surfaces for the space, but they remain surfaces when intersected/matched.

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Thanks! Not exactly a solution, but an interesting workaround.'s avatar  ( 2015-01-13 11:53:03 -0600 )edit

answered 2015-01-12 21:16:56 -0600

updated 2015-01-12 21:17:44 -0600

@Eric Ringold's solution is correct. The intersect feature in the SketchUp plugin uses a native intersect feature of Sketchup that looks for adjacent and splits the surfaces. Then OpenStudio just uses the same observers that exist when you draw new surfaces to classify it as a base or sub-surface. Since a base surface can't be contained within another base surface it is classified as a sub-surface. If you forget to split the surface as Eric described, you can always split it after the fact and then erase and re-draw the sub-surface. This time it should be a base surface.

However, there is a much nicer solution now if you are willing to do surface matching in the OpenStudio application with a measure as described in this post. The native OpenStudio measure splits up the base surface for you.

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Thanks guys! This will definitely work for now. We've got another employee working on the OpenStudio method so we can compare the two and figure out what's best for our workflow.

As the son of a computer scientist, I'm fairly disappointed in the execution of the tool in the SketchUp plugin. I understand now WHY this occurs, and its the same problem I have with most software being written today. Rather than examining the use case and developing an end-to-end solution that understands the goal of dividing surface, the intersect tool is just replicating human inputs. Ah well, free is free.'s avatar  ( 2015-01-13 11:52:11 -0600 )edit

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Asked: 2015-01-12 20:13:51 -0600

Seen: 1,195 times

Last updated: Jan 12 '15