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.