I’ve been researching Position maps recently and would like to know.
What can they be used for
How to use them (An example please)
I can make 3d objects and generate a position map to play with…I can orbit around it and it looks like a point cloud same as nuke.
All I can find is vague discussions and I know Nuke artists use them to position 2d objects in 3d space.
For the life of me I can’t figure out how to do that in flame. Are we missing a tool that converts a point in space into a axis location or something?
Any info you have no matter how small might be useful.
Thanks
Tim
P maps are a very cool tech in theory but don’t get used that much in practice. Almost all use for them is to create masks for color grading CG elements. Though, Cryptomatte has made this redundant in a lot of cases. If you want to try it, there is the LS_Posmatte matchbox, which a nice simple but effective tool for that.
One thing I sometimes do is use the individual channels from the P pass to creat general mates. Like if I want to create a rim light effect for multiple CG objects, you can take the red channel and grade it so only one side is white or do the same with the green channel for the Y position. But a lot of that functionality can be accomplished using relighting tools and Normals pass. So, it’s also usually not worth the effort.
In terms of positioning 3D elements using a p-pass you need a render, the render’s corresponding p-pass and the camera used for the render. Then add the render as an image in action, add the p-pass as a position, then import the camera and set that cam as the render cam in action. Looking through the cam there will be a degradation but orbit the working cam or look from an orthogonal view like the top and your render is unwrapped into 3D space as seen from the camera eye.
From there it’s super simple to place things spatially correct as objects move through your scene. The example that always gets thrown out is 2d textures of dust or powder charges based on a top view of a 3D creature walking through a scene, but I’ve used it for small rubble or debris and smoke around objects. It’s by and large a utility pass.
Don’t know if that helps all that much but there you go.
Grass:
This is where most of my time was spent. I ‘stumbled onto grass’ while experimenting with hijacked position maps (ask Philippe), and found that with a flat surface set at high polygon resolution, with tiny matchbox dots mixed into the position map, you get lots of fine 3D spikes. I developed a 3d mohawk and some pretty decent fur, but could find no use for it in this spot, so I went with grass.
Haha, oh that. Yeah there are tons of creative “3D” things you can do in Action with position maps (lots I never showed), but I still haven’t found a fine-quality use for it in real paid work.
Though I have learned some interesting things from this thread.
Thanks everyone for the input on this, and thanks Peter for the shout out!
World Position and Rest Position have been part of standard CG utility passes for regular VFX work. They are esencial for extended manipulation of cg render through mattes or relighting. Flame can definitely have a better toolset for working with these.
Here an example of how Mistika does it (around the 25:40 mark:
In Nuke, deeps bring Position, UV, and Normals to a new level, since you don’t get common artifacts from antiliased and motion blurred pixels. Not as common tho.
