Goliath20 posted a topic in General Houdini QuestionsHello, Does anyone know how to get a motion vector AOV for a VDB pyro sim in Arnold (Maya). I know the smarter solution would be to use Arnold for Houdini or to just use Mantra but I have no control over this pipeline. The VDB MUST be taken into Maya to be rendered with Arnold, and I MUST do motion blur in Nuke using motion vectors. I'm aware that in order to get motion vectors out of Maya I need to turn on motion blur in the render globals and make sure 'ignore motion blur' is ticked in the render overrides - I can render motion vectors for geometry and fur without any problems but I can't figure out how to get motion vectors for VDB's. Hopefully someone out there has had to deal with this before. Any help is appreciated, thanks.
Giving it a quick look, found some problems. -Set your filecache 'filemode' to write, not read. Also, when writing out a VDB, you have to change the extension at the end of your filename from .bgeo to .vdb -Plug 'dopimportfields' node into a 'convertVDB' node to convert it from a regular volume (which is what it is when it comes out of the sim) to a VDB. Make sure you select VDB from the dropdown box. In the group section, select all the fields you want converted to VDB. Also, in the 'dopimportfields' node, untick the fields you're not going to use (if you're taking this over to Maya, then you're probably not gonna need rest, rest2 or fuel; all this useless data is just going to take up disk space unnecessarily.) -The 'VDBvectormerge' node will turn your 3 velocity fields into 1. Just leave at default settings. You can ignore the warning it gives you. The 'primitive' node can compresses your VDB into a 16 bit format which is all you need. These two nodes aren't necessary, you can skips these two if you want, but they'll help you if you're working on a heavy sim. You have an OUT null at the end of this, I didn't look at your whole file but I assume you want to use your campfire sim to do something else afterwards. If so, you're probably going to want to put the OUT node after your dopimportfields and use the Houdini volume data, not VDB data- i'm just guessing here, maybe you don't, maybe you do want to use the VDB data, don't let me tell you how to live your life.