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surface parameter space orientation

Hugues De Cougny's picture
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Hi:

I am having a hard time figuring out if orientation of surface is always same (or opposite) as orientation of associated (u,v) parameter space. In other words, does the normal to surface always point in same dir as du(cross)dv. Usually, geometric modelers will give you that info (same or opposite) via some api function, but I cannot find anything like this in CAS. I can only assume that they always point in same direction, just to follow the convention used for curves, but I would like to have confirmation. Please, note that I am referring to a surface not a face (which has the added complication of the forward and reverse orientation w/t to solid that uses it). By using term 'surface', there is no possible confusion since it does not depend on any solid using it.

thanks for your help, hugues -