Strange collision map on FBX import

Development World Creation
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1

Hi!

We are early in setting up FBX import pipeline for various industrial-type images. I am getting strange collision plane on import of [S_R_Undercarriage2_UnrealCollisionError.fbx][1]. A larger file is included as well [S_R_UndercarriageFull_UnrealCollisionError.fbx], but if we import these with CombineMeshes=OFF option, the problem remains.

  • Import of “Undercarriage2” with scale=1.0 results in degenerate/infinite vertical collision plane orthogonal to the actual component;

  • MeshEditor > Collision: Simple Capsule or Box collision work well, AutoCovexCollision works really well, but 10DOP, 18DOP 26DOP make infinite vertical plane (is that the default collision algorithm on FBX import?);

  • Import of “Undercarriage2” with scale=0.2 results in no collision map;

This is not a show-stopper :slight_smile: we clearly don’t care about collision around individual component, and would generate combined collision map using MeshEditor > Collision > AutoCovexCollision or such … but still wanted to inquire for the purpose of debugging our FBX pipeline if problem is on our side, or help making UE4 more robust if the problem is on the algorithm’s side.

Is there there is something wrong with “Undercarriage2” that generates strange results above, or is it UE4?

  • Tested on 4.7, 4.8.2 and 4.9-preview

Thanks for great product and fantastic hands-on support!

ATTACHED: [1] s_r_undercarriage2_unrealcollisionerror.zip

2

Hi -

This is a “limitation” for the Simple DOP Collision models and using flat planes without clearly delineated border vertices. The DOP collisions look at the vertices and try to generate a collision mesh with enough detail to match the detail given with the detail restricted (10,18,26). Since your plane is actually at an angle as well, the DOP collision tries to take that angle into account as well which is what generates the large triangular aspect of the collision mesh (it is a triangular plane on creation, you can rotate you camera around the mesh to see this.)

For an item like this, I would first recommend using a flat plane with the holes alpha-ed out via texture, but if that is not possible and you need collision for individual pieces I would do custom collision in your FBX which will import when you import the mesh and override the generated collision.

Here is some good documentation on the subject:

Thank You

Eric Ketchum

3

Thanks, Eric:)