VARKON Version 1.15 1997-10-16

### Low level evaluation of curves and surfaces

VARKON includes a low level geometric evaluation routine called eval for those who want to know all there is about a curve or surface.
For any curve you can evaluate its position, derivatives, normals, curvature and torsion anywhere on the curve. The second derivative for example is calculated in the following way....
eval(curve_id,"D2RDT2",value); ! Second derivative with respect to curve parameter t
For UV-curves you can also calculate derivatives with respect to the surface U and V parameter and geodesic curvature.
For a surface the eval routine can be used to calculate a large number of geometric data including all derivatives and curvatures. The Gaussian curvature is one example...
eval(surface_id,"GAUSSIAN",value);

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