The Question;
In rhino curve extraction, what is the logic behind to pick a starting point when extracting a curve? I have no control over where the start of a curve is, is it randomly picked?
The need;
to control where will be the starting point when extracting, or making a curve from points or else.
Why this is important?
When you revolve a curve, the start point or Seam is controlled by you.(obviously)
When you extract a curve and say extrude, the seam position is… random(?)",
The problem;
This is a curve starting point related to blendSrf problem. but there could be many other cases for this, i don’t know.
When you want to blendSrf between that revolved srf to extracted curve’s srf, either you break the flow or split the extracted surface edge. example:
a revolded surface and a loft-ed surface from set of extracted curves.
loft surface does not allow a good seam flow because of crvstarting point.
you split the surface curve if you manually edit the control points for BlendSrf
No. Nothing like that in Rhino is “random”. All curves in Rhino - including those that define edges of surfaces etc. - have a defined start and end point. The curve start points from extracted objects will be the same as the start points of edges they were extracted from.
In your BlendSrf example the initial situation Rhino tries to connect the corresponding edge start points. You obviously do not have a seam point in the middle of one side of your rounded rectangle, so you need to tell Rhino that you want to put the point there manually.
I apologize. for any surface that has a seam the starting point is obvious, so let me give more examples:
section (joined lines) from polysurface and a cube with point shows crv start.
as shown here, I want to know how rhino picks a curve starting point.
converting a polyline to a G3 curve to demonstrate how rhino picks a starting point.
Also creating a curve from points/CtrlPts picks a point where I didn’t understand why rhino begins curve’s starting point from there?
thats why this breaks the workflow of BlendSrf.
note: (this is tested both in RH5 and RH8, I get exact results.)
