John John

jsmack

GlennimusPrime
By the way, what is the 3rd uv attribute for?

Why would a single vertex need more than two coordinates? I assume it only needs a u value and a v value.

What does the 3rd one even do?

It's just one attribute, you can't delete a component. The attribute can be replaced with a size 2 attribute using attribute create if needed, but most uv tools in houdini expect 3 coordinates.

UV uses three coordinates for the same reason it's useful to use 4 coordinates to represent 3 dimensions. The third being 'w' which can be used to represent an imaginary axis. It allows for rotations uv coordinates on arbitrary axes to be reversible. A matrix could be used to represent the mapping from one space to another, such as for projective spaces. The third dimension stores the projective z axis.