057 Position pass tracking

- [Steve] Hi, this is Steve Wright,…welcoming you to this weeks Nuke Nugget…how to track a 3D object to a CGI render.…The idea is to use the position pass,…which contains the XYZ location of each pixel…to position a 3D object.…Nuke Nuggets are often short little techniques…but occasionally I like to mix in some next level…techniques like this.…Okay, to do this,…you have to have a CGI render with a position pass…plus the camera.…Here's the camera that did the original CG render.…

This is just a 2D EXR file.…There's no geometry here,…and I can show you my position pass right there.…Okay, so let's get to it.…What we want to do is sample from this position pass…the XYZ location frame by frame…and feed that to a piece of geometry…so it'll track right on top of this surface.…All right, here we go.…In order to see what the original geometry looked like,…we can use the position to points node.…

So select the read node, go to 3D, Geometry,…Position to Points.…And then I'll tell it to go look for…the position pass in the position pass.…