Hello,
sometimes I have the problem, that rebuilding a crv will lose its symmetry. How can I prevent this?
I have the feeling “select master curve” could help here but the rhino help site doesn’t help me understand how to use this button.
The crv you see on the picture was created with Crv2View so it has so many points… I want to simplify this crv now.
Can somebody help? Thank you 
If you rebuld only one half, obtained by splitting the curve with the symmetry line, and enable preserve end tangent directions, then mirror the result in the symmetry line and join both halves the result will be symmetric.
Use CrvSeam to drag the seam (start/end point) of the curve to the line of symmetry. Rebuild should then be symmetric if the curve is symmetric.
Rebuild interpolates through the input curve at a number of points equal to the number of specified points in Rebuild. For a closed curve the locations of the interpolation locations are determined in part by the seam in the input curve. If the curve seam is not on the symmetry line the input locations will usually not be symmetric.
If you still have problems post a .3dm file with the input curve.
