Note: Evaluating parameters at equal intervals in the 2-D parameter rectangle does not necessarily translate into equal intervals in 3-D space.
Surface evaluation Evaluating a surface at a parameter that is within the surface domain results in a point that is on the surface. Keep in mind that the middle of the domain (mid-u, mid-v) might not necessarily evaluate to the middle point of the 3D surface. Also, evaluating u- and v-values that are outside the surface domain will not give a useful result.
Normal Vectors and Tangent Planes The tangent plane to a surface at a given point is the plane that touches the surface at that point. The z-direction of the tangent plane represents the normal direction of the surface at that point. Grasshopper handles NURBS surfaces similarly to the way that Rhino does because it is built on the same core of operations needed to generate the surface. However, because Grasshopper is displaying the surface on top of the Rhino viewport (which is why you can’t really select any of the geometry created through Grasshopper in the viewport until you bake the results into the scene) some of the mesh settings are slightly lower in order to keep the speed of the Grasshopper results fairly high. You may notice some faceting in your surface meshes, but this is to be expected and is only a result of Grasshopper’s drawing settings. Any baked geometry will still use the higher mesh settings.
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