Sweep2 to a Point

Rhino hates three-sided surface. OK.

What about Sweep2 to a point? That results in a 3-sided surface. Does that mean it creates something that really should be avoided or does it have some mechanism to avoid problems>

Hi Jim - Rhino does not hate… there is nothing inherently wrong with surfaces that come to a point by compressing to a singularity - Rhino is a tolerant liberal on that score. However, these can present problems in certain circumstances because the curvature across the surface is apt to increase dramatically near the point, making smooth transitions difficult on those areas - maybe that is what you meant? Sweep2, to a point, Extrude to a point, loft to a point, EdgeSrf with three curves, SetPoint, can all make these…


The topology of the surfaces is still 4-sided, but the zero length edge is called a “singularity”. They are valid. The problem though is strange things happen as you get close to them. ProE avoids them entirely by extending the surface past the point where the surface self-intersects, and trims it back to the point.
As you gain modeling experience you’ll figure out what circumstances are fine with surfaces with singularities, and others will do better to be trimmed to the shape you need.
Rhino’s Sphere is a single surface with two “singularities”, and a “seam”.
A “seam” is two opposing edges of the same surface joined together.
A Cone is a single surface with on singularity, one seam, and a “naked” circular edge.