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The surface tolerance is the distance between the facet and the part of the surface it is representing. By setting this refinement, the user specifies how accurately the facets represent the surface. It is desirable to provide surface tolerance when facets obtained with normal tolerance do not represent the surface well.
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The
set_surface_tol method from the
REFINEMENT class specifies the maximum distance between a facet and the true surface. The proper value is dependent on the model size. When the surface tolerance is set to -1, the faceter will use a surface tolerance that is independent of the model size. This is a fraction (e.g., 1/1000th) of the diagonal of the bounding box of the face. This results in faceting that is independent of the units of measurement of the face.
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Figure 1-2 illustrates two cases of surface tolerance. The refinement values are specified in Table 1-1. In the first case the surface tolerance is zero, meaning that it is not taken into account in faceting. In the second case the surface tolerance is 0.1, meaning that every facet is not more than 0.1 unit away from the mathematical spline surface. In the second case there are smaller but more facets in order to satisfy the surface tolerance constraint.
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Figure 1-2. Surface Tolerance
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Table 1-1. Surface Tolerance
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