Hello,

I've been wrestling with this for a couple of days now and I'm at my wit's end. When I sim my mesh of a shack collapsing (I'm just keeping it basic for now by just hitting play and letting it all fall apart)and export it into UE4, the imported FBX has all of my sub elements sitting at the origin instead of their correct positions, and it looks like they're rotated 90 degrees on UE4's Y axis also.

For some background to my issue and what I'm trying to do, I will say I've followed the “traditional” method I guess you could call it of voronoi fracturing a mesh (pig head test mesh), simming it, and exporting into UE4 (following the Houdini for Games // Houdini Illume Webinar by Luiz) with no issues, all working perfectly which is nice, but I want to sim a pre-fractured mesh getting blown apart and so on without fracturing it within Houdini.

I tried importing my building FBX, selecting all of the sub meshes, and clicking the RBD Fractured Object button in the Rigid Bodies shelf.

So now whenever I export my new shack sim of pre-detached pieces, they are all placed at the origin. I managed to somehow fix the position issue, by ticking either “Keep position when parenting” and “Child Compensation” within the transform tab of my Geometry Subnetwork, or some combination of the two, but regrettably I can't reproduce my own fix…

When importing my FBX into Houdini itself I've tried ticking and unticking “convert to Y-up Coordinate System” which doesn't seem to make any difference.

What's even better is that if I import my FBX into Houdini, and directly export it without editing it in any way, then import this FBX into Unreal it looks normal. The scaling is also correct when not touching it… however, when I was trying to RBD sim the mesh before exporting, I'd uniform scale my mesh subnetwork to 0.01 to have a correct object scale and for some bizarre reason exporting this 0.01 scaled and simmed version, ontop of all my sub objects being moved to the origin it's also huge.

Hopefully I'm making sense as to what the problem is, my brain is fried and I'd appreciate any help to get this working. I tried to attach my .hip file in case someone wants to take a peek but it's 20mb and so too big.. here's a link instead: http://puu.sh/C2dSs/8959779fc4.hip [puu.sh]

Any help would be appreciated, in fact if there's a totally different way to do this I'm all ears as it seems like there should easily be a way to separate my mesh into the pieces I want inside Houdini to sim it instead of using Voronoi as basically every tutorial has shown so far, but I'm not experienced enough to know where to start.

Hi. I made a couple changes to your file.

1. Object merge all the geo from the fbx import. This is a lot easier to manage than the bazillion nodes you have coming into the dopnet. This also sets up the local space of the transforms which could have been causing the issues you were having with everything ending up at the origin.
2. Use a dopimport to extract the sim geo to a geometry container and use that as your export. I think pointing to the dopnet directly doesn't play nice with the Vertex Animation Texture node.

Mike

https://drive.google.com/open?id=1VqH2KiVfvDU1aVHIufw0sT63MeUJHC10 [drive.google.com]

Hey Mike,

Thanks for looking into this for me, it works!

I have a few questions as there are some things I don't understand, namely what's going on inside the merged_building geometry network. For example you use: s@name = “piece” + itoa(i@class); in a primitive wrangle. What's this doing and why isn't it enough to just use the object_merge node? If you could explain the flow through this network and why you're doing those things that would be great. All the other stuff I understand though.

Additionally I'm completely clueless when it comes to VEXpressions. Where would the best place to look for learning how to use them be?

Again many thanks for looking into this for me and getting it working

Cheers