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Geodesic curve offset
johan_van_ravenhorst
Member Posts: 19 ✭✭✭
Requested feature summary: A geodesic offset of a given curve on a given surface at a given distance in a given direction.
Example application: Modeling of wind turbine blade composite layups, especially draping of fabrics, preventing detailed draping simulation. For an example and a possible workaround, see Figure 1. In Solidworks, the workaround often resulted in erroneous behavior (back in 2010, maybe it has improved).
Example application: Modeling of wind turbine blade composite layups, especially draping of fabrics, preventing detailed draping simulation. For an example and a possible workaround, see Figure 1. In Solidworks, the workaround often resulted in erroneous behavior (back in 2010, maybe it has improved).
Figure 1: (left) Example of a geodesic offset of curve C on surface S of a wind turbine blade, yielding geodesic offset curve O. (right) An approximation using multiple swept surfaces. (bottom) Mathematical expression, coarsely defining a geodesic offset curve. Note that the path of arc length d is generally not coplanar.
Putting the sketchy math of Figure 1 in words: Curve O is a `geodesic Offset curve´ from curve C at arc length d, if, for each point q on curve O, there exists at least one path p on surface S from point q to curve C for which it holds that the arc length of that path equals the geodesic offset distance d, and, for each possible path p on surface S from point q to curve C it holds that the arc length of that path equals or exceeds the geodesic offset distance d.
This problem may be relatively exotic as well as relatively `computationally expensive', so I do not expect a high implementation priority. However, maybe this request can be taken into account when selecting libraries or algorithms for similar operations.
The accuracy of the approximation improves with a decreasing sweep profile radius, provided that the surface-surface intersections are precise enough. In Onshape, the "split face" feature could be used to achieve the approximation, but there seems to be no option (at this time of writing) to keep the sweep profile normal to the sweep path.
PS: I was completely shocked (in a very positive way) when I saw OnShape for the first time in my life this week. It addresses many headaches that make CAD-life miserable. I could not believe that this CAD system strategy would work so well.
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Erratum: In the right figure, swept surface S should be swept surface R.