Loft v. Extrude

Something that has puzzled me so I thought I would ask.

In the attached I have three identical closed polylines. At the top I have lofted a pair.
At the bottom I have extruded one.

The loft has created a separate surface for each curve segment.The extruded surface has the two upper facets merged. Why is that the case?

Problem Loft 6.3dm (3.1 MB)

Hi -

To ensure that this is created as two separate surfaces, run the CreaseSplitting and select the Enable option before running the ExtrudeCrv command.

I’m not getting any difference.

Hello - the file angle tolerance is .001, the polyline segments are ~.7 degrees off,


so Loft does not merge those segments. Extrusions use it’s own tolerance, apparently - if you set useExtrusions to make polysurfaces, you’ll get the same as the loft, or if you set the angle tolerance to 1, the loft will merge the segments.


Thanks, my preference is to not merge the surface as that is a specified knuckle point.

UseExtrusion=PolySurfaces does add the knuckle to the extrusion.