Blend 2 curves with a definied high

Rhino Rhino for Windows
1

Hi, I would like to know the proper approach for blending 2 curves creating a connecting curve with a maximum definied high or passing trough a definied point. The apex of the arc should have a maximum high of “x” from the ground like working with catenarys . I tried to scale 1d afterwards the blend but I think it´s wrong

21

2

Hello,

this depends on what you want. some possibilities:

  • blend command and with shift pressed on the second control point you can move it very close to the desired position.

  • If you need accurate blending you can use _HandleCurve to define G1 blending’s.

  • You could also use _parabola3pt or _interpolate, increase degree to 4 (G1) or 6 (G2) and match (its one more degree as needed, because you want an additional control point for control.

  • split blending in two half’s, if you tangent align the last two cps of two symmetric curves, where the tangent is going through the point, you always get G2 in-between them, due to symmetry

3

I see 2 ways if you need to draw catenary

  1. use mathplugin for rhino 5 with following settings: x=t, y=cosh(t), z=0,
  2. You can generate more points in any spreadsheets (equation is “y(x)=cosh(x)”) , export the calculated values as csv, import this file into the Rhino a use “LineThroughPt” command to draw the curve

edited: I discovered the command catenary was added as new command to Rhino 6.

5

Why? I think that might be the most accurate way, assuming the start points of your blend are at the same Z height. Make a point at the quad osnap of the blend, SetPt a copy of it down to the target Z height you want and another copy down to the Z height of the start/end points of your blend. Then Scale1D from the quad point to the desired Z point, using the last point as the base point. You don’t actually need to create the points if everything is lined up vertically, just to illustrate the concept.

–Mitch

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