Tolerances, tolerances, tolerances...?



I have a strange situation illustrated below:

  1. Two joined surfaces into brep. Both sides are planar.
  2. When I ask for naked edge I get boundary with no interior edges.
  3. I untrim surfaces
  4. Get intersection line.
    And it is not the same as brep edge. Why?

Rhino 6 wip

units.3dm (3.2 MB)


Could be a result of tolerances maybe, although that’d have to be quite extreme.


Yeah it is really strange, because those two quads are extracted from planarization and I can create planar surfaces and join them.

I am working in meters and the size of two faces is around 3 meters and from origin point up to 20m.


Your file tolerance is 0.01 meters and that is about the difference between the two lines. If you tighten your file tolerance it will probably be closer…



I would like to ask about tolerance in general as I had similar issue several times.

Having this kind of model what is the best tolerance working with meters?

before I had 0.001 which is 1 mm also similar issues occur.

Should it be really low 0.0000001?


Well, one way of looking at tolerance is that it represents the point which you consider a measurement to be too small to be significant to what you are constructing. If you are working in meters 0.01 then represents 1cm, thus you are saying that things that are off by 1cm or less are acceptable - and - that objects smaller than 1cm in any direction can be safely discarded…

Generally it is recommended to keep your tolerances in the range of 0.01 to 0.0001 (for calculation purposes), if you need tighter tolerances than that, it is recommended that you use a smaller unit. Maybe you might want to work in cm in this case…?