Mystery geometry

marko_vukovic

Here is some background information first on the origin of the sketch in question. I found an STL file that I wanted to tweak a bit. I split the part using a plane and created a sketch of the resulting profile with the "Use" command. That created a "curve", but it does not seem to be either spline nor bezier. My question is what kind of entity this is. This is the document with just a single sketch in it: https://cad.onshape.com/documents/294e109e59cb7c0832e5fe9d/w/2aa7362dda57360daad0d84a/e/52ede2a468f535e038631fa5

martin_kopplow

Looks like it is a mesh face rather than a curve. It appears to be made up of small line segments. Is has no curvature ..

GregBrown

The sketch curve in the link ^^^ is in fact a spline. It happens to have an extreme number (1639) of control points, so I suspect it will not be particularly useful or clean as you would like. However ,it would be easy to recreate it with a few parallel lines and a bunch of fillets. But then again it all depends on what you want to do with it after??

martin_kopplow

Looks like it is a mesh face rather than a curve. It appears to be made up of small line segments. Is has no curvature ..

GregBrown

The sketch curve in the link ^^^ is in fact a spline. It happens to have an extreme number (1639) of control points, so I suspect it will not be particularly useful or clean as you would like. However ,it would be easy to recreate it with a few parallel lines and a bunch of fillets. But then again it all depends on what you want to do with it after??

james_aguilar160

Looks like lines connected by tangent arcs to me. But there's no reason it has to be something that Onshape can easily create in sketches. In the limit, you could have an STL file whose cross section was sculpted, which would not correspond to any mathematical principle other than being exactly what it is.

marko_vukovic

Thanks, I can see it myself now after I have zoomed in close enough.

marko_vukovic

Yes, I was planning to approximate it with lines and arcs, or fillets as you have suggested. But I am curious how you could tell it was a spline. I could not see any obvious indicator of it, but I am just starting with Onshape so I suppose I could be forgiven. That was why accepted the previous answer at its face value thinking a "mesh" was just another type of entity that I needed to look up.

marko_vukovic

james_aguilar160 said:

Looks like lines connected by tangent arcs to me. But there's no reason it has to be something that Onshape can easily create in sketches. In the limit, you could have an STL file whose cross section was sculpted, which would not correspond to any mathematical principle other than being exactly what it is.

If those had been connected lines, I would have been able to select the individual segments in the sketch. But when I click anywhere on it, the whole contour is selected as one entity as indicated by the mouse pointer.

martin_kopplow

Yes, it is in fact a strange creature. It has no start or end point, it has no pickable segments and it has no support points or handles, like you would expect from a spline. When working with it, it behaves like a spline that has no tension between points, thus the connection between corners is always a straight line. Other than out of pure curiosity, I would not bother trying anything with this but just recreate it as accurate sketch geometry.