Non-Orthogonal Lines Appear Orthogonal in Viewport

Ever since Rhino 6 was released I have been dealing with some perplexing issues surrounding nearly but not quite orthogonal lines that I think I finally figured out. It appears that Rhino 6 is doing something in its viewports that is causing nearly orthogonal lines to “snap” to being orthogonal even if the geometry is not orthogonal. This is causing problems in some cases where the appearance of the line and the actual location of the line is off by a few pixels, making snaps unpredictable and mistakes or imperfections in the geometry hard to catch.

I’ve attached a screenshot to help illustrate. In this screenshot we are looking at a radial grid of lines in perspective. they are evenly spaced in reality, but they are appearing to have a much larger gap between the lines right as the lines near being orthogonal.

Hello - can you please save a names view that shows this and post an example file, or send to


Here is an export that shows this happening with a named view called “View Error” that shows it happening
181116_NonOrtho.3dm (321.7 KB)

I also noticed that the effect of this is more pronounced when you have geometry in the scene that is sitting a little bit away from the origin, but something that is even at a pretty reasonable distance will do it. In the example file, everything is within 1000 units of the origin. I also tried changing the document tolerance to see if it might have some effect - my document was at a fairly high tolerance to work with fabrication level tolerances - but the bug still persisted.

I’ve also had a lot of problems with this when working with imported surveys and GIS files where lines are nearly orthogonal, but not always perfect due to real-world conditions.

As a temporary test, in Rhino Options > View > OpenGL, uncheck the option for using GPU Tessellation.
This will slow down Rhino’s display engine, but does it clear up the problems?
Please remember to turn it back on for better performance.

Does this change anything?

It did not, here…

No, GPU tessellation does not change anything.

Okay, thanks.