Hi,
I have a simple closed planar polyline. And I get Unable to calculate area.
I attached the file.
Hi Bogdan - it seems the curve is not quite planar.
-Pascal
But it creates a planarsrf …
Yeah… I guess it is a matter of tolerance - the file tolerance is 1 unit, which is a bad idea - try to work between .01 and .000001.
https://wiki.mcneel.com/rhino/faqtolerances
-Pascal
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Thanks! I used to work in 0.1 but (as I remember) I was running into other kinds of problems.
Hi Pascal, if a surface was made from that curve , could that then be used to get the area?—-Mark
Hi Mark - yes, no doubt… but still…
-Pascal
That polyline came from a previous surface actually (dupborder). And the surface came from Brep/Plane section in Grasshopper. 
And grasshopper tells me that all Z coordinates of the control points are the same …
According to Bubble for Rhino the curve is not planar. After usingsetpt command with checked z direction the bubble for rhino shows the curve is planar and calculates the area.
@DavidRutten is this a Grasshopper rounding issue? I’ve noticed before that Grasshopper often flags curves and surfaces as planar where Rhino doesn’t.
It could be rounding, certainly the coordinate display will not show differences which are below some level of tolerance, but those differences may still affect planarity checks.
Tolerance issues will come into play here, as Brep|Plane intersection actually relies on Brep|Brep intersection behind the scenes.
Yes, I notice that tolerances affect intersections most of the times.
@pascal, now I remember why i changed the tolerance to 1.
Here’s the discussion:
I think that it could be useful to fine-tune the tolerances settings for large scale mm template.
They also affect Make2D.