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Specify method for the UV parametrization
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Use current UV data - In this case it is used the texture coordinates which are already set. This method can be useful for the models which come from other programs, where the texture coordinates were set (on the picture below it is possible to see the example for the model from SketchUP).
LSCM (Triangles) - Least Squares Conformal Maps is a more complex algorithm, which allows us to receive better unwrapping results. There is one important restriction for the current implementation of this algorithm, namely all facets must be triangles.
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