tolerance problem with line-plane intersection

I'm having a tolerance problem with the line-plane intersection command. If I ask the intersection points of 4 lines with a plane and use these to draw a polyline then the polyline is not planar! this occurs when the coordiantes are very big (>10^3) if I set the drawing in meters then I don't have this problem. I tried changing the tolerance and precision in Rhino but this seems not to have any effect. Is there another way to deal with this so I can keep working in mm instead of m?

Tags: intersection, line, plane, tolerance

Attachments:

meters.3dm, 26 KB
mm.3dm, 25 KB
toleranceproblem.ghx, 153 KB

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Permalink Reply by David Rutten on December 5, 2010 at 7:22pm

The deviation from planarity is 4.5e-12. This is an absolutely tiny difference (especially considering mm).

I'm far more worried about the display degradation between the Grasshopper geometry and the native Rhino display when I bake those curves.

--
David Rutten
david@mcneel.com
Seattle, WA

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Permalink Reply by piet lelieur on December 6, 2010 at 3:08am

David,
thanks for replying, I'm working in meters now and the problem doesn't occur any more. the planarity problem is especially annoying when offsetting a closed curve (then the result isn't closed anymore). What I don't understand is the following:
when I work in mm with a precision of 1e-12 there is a problem
when I work in mm with a precision of 1e-21 there is no problem

I tought the display degradation was an openGL isue and not a grasshopper problem, but I don't no much about opengl...