Hello,

I've started learning Houdini. I'm doing the first step Light, Shade & Render tutorials and have a question about shading.

I've noticed that some VOP nodes want position as an input (eg aanoise), some want S&T as an input (eg. checkered) and some want UV as input (eg colormap)

Can someone explain the differences and/or uses of these three options?

I noticed that the UVCOORD node also outputs S&T. after some experimenting i noticed that they seem to be different than the global S&T. Why is that?

Martijn

Position input in aanoise means you should define 3D position or 2D or 1D as input.
If you are in VOP SOP , so you should define X Y Z position as input.
But if you are in the SHOP , you have 2 different choice , use P as input (P means position of each point in the 3D space) , or you can use UV as position (in this case your noise is independent of Point's position).
e.g if you use Point Position as input for aanoise for Shader , you take different result if you move your object in the 3D scene , and that's not good for shader , In this case you should use UV for input , in this case you take same noise in the shader.

UV means local UVCoords.
ST means global UVCoords.

local UVCoords :
that you create in the SOP network with UV tools like “UVTexture” and “UV Project” nodes.

Global ST(UV):
means if you don't use UV nodes such as “UVTexture” , “UV Project” and etc in the SOP network , then each face has different uv from 0 to 1 by default .
for example in the “Grid SOP” you take different result if you change Row and Column parameters.

So if your node need UV as input like ColorMap , you have too define UVCoord for input manually , If not , You take wrong result.

But if your node has ST as input like checkered , In this case if you don't define any UVCoord for input , this Node (e.g checkered) use global UVCoord automatically and you take correct result in the rendering (But related to Topology and Face Count).
:wink:

Thanks for the answer,

I think I understand it better now.

in SHOP, both UV and ST are relative to the surface, so they won't slide when geometry deforms or changes. ST is always available, UV not always.
POS is relative to the objects position (I suppose). it moves with the object, but not with changing geometry.

Yes , Exactly , Also I made a simple example about this for you :wink:

Thanks for that example. It's much clearer for me now.

mart1jn
Thanks for that example. It's much clearer for me now.

:wink: