In the attached file I have a curve I created with curvethroughpoints with degree one. I have then run simplycurve on it several times. Yet obviously colinear segments are not being merged (see second layer with exploded file (unless I set the tolerance to a huge value).
Problem Simply Curve.3dm (3.9 MB)
Here is a similar example
Problem Simply Curve 2.3dm (3.9 MB)
I stared with a 4 arc and 2 line polyline. When I do simplycrv, two of the arc merge and two do not. I can explode and join those two arcs and simply them separately. The previous may be a tolerance issue but this one is not.
That is because the start/end point (the curve seam) is in between the two arcs… SimplifyCrv does change curve seams.