@pbacot said:
I guess my experience is colored because I use my own CAD drawings and I don't generally have problems in accuracy. But I have seen where the accuracy of an import can be undetectably off--until it causes problems in working the model (closing faces etc.) later on.
fwiw, when i realized the accuracy issue, it was when i was first learning rhino using a template with feet as the units and a tolerance of .001 unit (so, lower tolerance than sketchup's 1/1000th inch).. i brought it into sketchup and for a minute, thought sketchup was more accurate than rhino since everything wasn't exactly in place in sketchup (out of whack enough to get a 'don't panic- there's a problem.. should i fix it?' message..
which eventually led me to realize the tolerances in rhino were adjustable.
but 1/1000th unit is a good to high tolerance setting for most situations so if the original cad app was drawn in feet, it's likely their tolerance wasn't set tighter than .001 feet.. so that's probably the most notable scenario to look out for.
on the flipside, if the original modeler was using millimeters or centimeters at .001, you won't have any accuracy problems when bringing that into sketchup.
[but even then, this is assuming the cad model went through some trimming/splitting/boolean operations in the original application which is when these tolerance issues will readily show up]