Loft Surface Isocurves Best Practice?

Rhino Rhino for Windows
1

Hi everyone,

I am working with some curves and often I rebuild these curves to matching control point density.

Because one curve is long than the other, the loft isocurves instead of being perpendicular start to rotate.

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Which is the best of this three? A, B or C?
For what purpose you ask? In the first place, importing into Revit for visualization and drawing purposes. Later for fabrication purposes.

A: Normal Loft between top and bottom curve both with 68 interpolated points, degree 3. (Not sure why it places isocurves in pairs). Inclined curves.

B: Normal Loft between top and bottom curve with Rebuild of about 40 control points, degree 3. This time the isocurves are not in pairs, but also inclined.

C: Loft between straight vertical lines, which were created by dividing top curve and projecting that point onto the bottom edge curve. These vertical lines where then lofted horizontally.

2

Hello- I like C. You can also get there by projecting edit points (EditPtOn) of the rebuilt lines to the shaped curve and then lofting the two.

-Pascal

1 Like
3

I like the C too.
But this get me to a question: why loft is not able to get a clean srfs by default. The solution A shows so many overlapping isocrvs when the 2crvs have same CVs

1 Like
4

I would use Degree 4 instead of Degree 3 for the curves. The former is much smoother even after you edit the control points.

5

The following is based on observations and experiments. I do not have any direct knowledge of Rhino code or algorithms.

Loft creates a surface by matching points on the input curves with corresponding parameter values. (Points with corresponding parameter values means points with the same parameter value if the parameter on each curve was rescaled from 0 to 1.)

Isolines of the surface will intersect the curves at the locations along the curves with corresponding parameter values.

The surface will have a knot at the location of every knot on the input curves. If knots on the input curves have close but not quite corresponding values then the surface will have two knots which are close together. Isolines are displayed at knot locations so there will be isolines which are close together.

1 Like
6

You might want to try this method using the option Knots=Uniform when interpolating.
That should avoid the extra isocurves.

7

Thanks.
Make sense but not always.

9

When/how is the behavior different? I’d like to improve my understanding.

10

The Loft option “Rebuild with” uses uniform spaced knots.

11

Yes that was the OP’s method “B”.
However, that version has inclined isocurves.

If the goal is to get vertical isocurves that could be done by using the method in version “C” to produce the points and then use InterpCrv ( Knots=Uniform) to make both curves to be used by Loft.