Probably a stupid question - UV Mapping

[AFK_Matrix]

Hi,

 

I am currently learning Maya for my new job and I have to give Presentations on what I am learning. So I am giving a presentation on UV Mapping and Texturing and I have kind of gone blank on why the XY coordinates when your modelling are replaced by UV when you start to UV map the model?

 

Sorry if this is a stupid question but I can't think why.

[Jim Mann]

I seem to recall that UVW is basically XYZ for the texture transforms but relative to the object that the texture is being mapped to rather than the scene as a whole which would be described in XYZ. i.e. its a local rather than world coordinate system.

[shaneis]

Jim's quite right. To elaborate...

 

...why the XY coordinates when your modelling are replaced by UV when you start to UV map the model?

 

That's the problem right there - the XYZ system isn't replaced by UVW. They are two different sets of coordinates.

 

1. The XYZ set applies to how a surface occupies 3D - world space.

2. The UVW set applies to how a surface is mapped in 2D - local space.

 

UVW has no effect on the surface (the geometry) that exists in world space. The "W" component does have an effect on geometry in local space (eg displacement), 2.5D for argument's sake - depth in local space, not world space. (There are other instances, though not important at the moment).

 

Think of it this way - take an orange...

 

By using XY and Z coordinates, we can determine the orange's physical size, form and positioning in world space (ie: how big it is, what shape it is and where it is relative to the rest of the world).

 

By using UV and W coordinates, we can determine the location of the orange's surface tonal qualities, it's patterning and texture in local space (ie: how and where it is coloured, where any variations in transparency/ specularity/ reflectivity etc occur and the position of any surface detail occur relative to the rest of itself).

 

See the relationship? The orange's skin will remain orange and the little green bit from the stalk will remain green regardless of where you move the orange in world space - because the surfaces coordinates (UVW) are local. To this, if you were to select the orange's UV's and rotate them by 90deg, the little green bit would end up sitting somewhere around the "equator" - the orange itself will not move regardless of what you do to the UV's.