Explode Object component ignores blocks with invalid content

Grasshopper
1

After reading this topic, I thought I should mention this problem I experienced just recently.

The file I was working with is a building which was converted from *.ifc
It contains blocks, meshes and breps. One mesh in a block is invalid.

Since I was just going to shrinkwrap all geometries in the file, I thought I would simply use the Eplode Object component. Unfortunately the component fails to output anything if a branch contains an invalid mesh.

This can be problematic on large files with a lot of geometries.

image
image2312×1226 245 KB

I cannot share my clients file. Here’s an example with another mesh:

image
image2386×1060 236 KB

block_invalid_explode_problem.gh (19.1 KB)

2

in this particular case you can check the mesh for degenerate faces and reconstruct the mesh

image
image769×775 67.5 KB

this is done by custom script (i think there’s a rhinocommon function that does that, but i forget)

double click on the c# script for details
block_invalid_explode_problem[partial_fix].gh (24.2 KB)

I think a more robust version is possible, like checking face degeneracy by tolerances, but for now, i think this stands as a proof of concept

3

alas, here it is
CullDegenerateFaces()

4

Thanks for the cull degenerate faces script.

Nevertheless I’m not sure if the current behavior of the explode component is on purpose and I’m hoping someone from McNeel can take a look.

@kike is this something for you?

5

one explanation i could find for that behaviour is that the meshsphere ex component create 6 different meshes

image
image1087×497 88.7 KB

observe the seams

if you explode the baked mesh in rhino, it gives you 6 meshes

image
image819×659 186 KB

image
image533×510 78.2 KB

so even if you manually introduce a degenerate face in the meshsphere ex mesh, you still end up with the same seams

the real question is why the regular explode component in grasshopper doesn’t give you 6 meshes as manually exploding it in rhino

6

Adel, forget the mesh. Please. I’m not looking for a solution to fix the mesh.

@kike or @AndyPayne is this behaviour intended? Couldn’t the explode component output the invalid mesh?

7

I spoke with Kike and we both agree that it would not be the correct behavior to switch the explode component to return invalid objects. We feel that it is better to only return valid objects and make the user aware if there are invalid objects that were not exploded. To this end, the explode component will now return a warning if an invalid object is passed into the explode component with some additional information as to why that particular object was failing to return anything.

However, to ultimately get at a list of objects that represent what it is that you are after, it is possible to use a the Null Item component in tandem with a Pick N Choose component to reconstruct the list of objects. I’ve attached an example below.

image
image1293×656 77.4 KB

block_invalid_explode_problem_AP.gh (16.8 KB)

1 Like
8

Thanks Andy I think this is a good solution.