Loosing planarity when curve is transformed?

Hi, all,

Just curious why the curve is loosing the planarity when it is transformed.

1. Draw the planar curve on global plane.

2. duplicate the curve, and transform plane to plane into another 100 number of 3d position. (due to the different orient of plane, it is moved and rotated)

Now, some of the curve isn't any more planar. (but deviation from curve plane is really tiny)

Which step is causing to loose planarity? Is it due to the duplicate tolerance? or transform process?

Thanks!

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Permalink Reply by David Rutten on June 14, 2011 at 8:58am

Hi YJ,

very few floating point operations are exact in computing. Rotating and even moving an object will in some very small way deform it. When checking for planarity (or any other geometric and numeric property, distance, angles, equality, you name it) you should always define a tolerance. This has nothing to do with Rhino, just with the way computers deal with numbers.

In your case, you should not test for perfect platonic planarity. You should instead test for planarity within 0.1mm or whatever accuracy makes sense.

David Rutten

david@mcneel.com

Poprad, Slovakia