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4.14 imported UCX collision mesh distortion

Started with the "First Person Template" as a foundation for the project. I was handed a 3D model of a subway station built in Autodesk Revit. Imported it into 3D Studio MAX 2017 for UV mapping and UCX collision assignment. The model was centered around 1800 meters from the origo in 3D MAX. Exporting walls, floors and ceilings with their corresponding collision worked as expected in Unreal. The problems started when modeling collision for the stairs. Every import from 3D MAX either had missing faces or random distortions and gaps. After a while I tried moving the whole stair model to 0,0(origo) into 3D max before exporting the FBX. When brought into Unreal the collision mesh finally looked right. The render mesh itself never had any problems, only the UCX collision mesh.alt text

Attached are both a 3D MAX 2014 file of the offending stairs model and the exported FBX file.

I have been forced to restart the project starting with moving the whole scene in 3DS MAX to the center of Origo. The collision distortions are mostly fixed, but can still appear if the collision mesh is too thin(like modelling a very thin box for instance). For now this work around seems to hold, but it would be nice to know what is causing these problems.

Product Version: UE 4.14
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asked Nov 29 '16 at 10:44 AM in Using UE4

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I could be wrong, but if the teal object is your UCX, then it appears to have a concave area which would necessarily break the collision which needs to be constructed entirely of convex shapes. You may need to create the collision object out of two separate mesh objects, number them following Epic's collision numbering convention (described under Caveats and Considerations here https://docs.unrealengine.com/latest/INT/Engine/Content/FBX/StaticMeshes/#collision), and edit your import settings to allow "One Convex Hull Per UCX."

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answered Dec 01 '16 at 02:59 AM

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Timothy Gatton
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avatar image Waqas Dec 01 '16 at 11:23 AM

Hi Timothy, thanks for taking the time to reply. I wish it were a simple matter of non-convex collision mesh. but the teal UCX mesh is already broken up into two seperate convex objects. As you can see from the attached image the object exported from the origo comes in fine, while the other with the offset doesn't.

As a side note, if you do export a concave UCX collision mesh, Unreal automatically encapsulates it creating a convex mesh, so you never see a concave collision mesh in the editor.

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