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The local texture coordinate system (u,v)


Gilles

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I'm surprised there is not a definition of the coordinate system (u,v) in the original papers about the method PTM.

 

Could you explain the transformations between azimuth/elevation angles and the spatial variables uv (or between cartesian coordinates and the spatial variables uv)?

 

ie. How to pass the light positions (xl,yl,zl) (where zl takes the normalized value 1) to spatial coordinates lu and lv?

 

Thank you for your help

 

Gilles

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Sorry, I didn't read this : "The local coordinate system is defined per vertex, based on the normal and on the tangent and binormal derived from the local texture coordinates"

 

But I don't understand. Have you an exemple in order to illustrate this projection?

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Gilles,

 

Sorry if this wasn't articulated well in the 2001 Siggraph paper. To figure out what your Lu, Lv values are, construct a vector that points to the light source from the center of the image. The first coordinate of that vector is measured along the x axis of the images, the second is along the y axis of the images and the 3rd is perpendicular to those two, pointing up. Now normalize that vector, which is just dividing each of those components by the length of the vector. You should now have each component being between -1 and +1, and their squares adding up to 1. Now just drop that last component, the first two are the Lu, Lv coordinates that specify the lighting directions.

 

cheers,

 

Tom Malzbender

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