Split precision

Please excuse my ignorance, as an architect I normally don’t work on projects that would cause issues like that:

Currently I am working on a very complex stair, they want to build the concrete casting forms from my 3D model, so I am trying to work as precise as possible. Now I found that when I split an object, in this case a bunch of polysurfaces, with another object, in this case surfaces, the result looks good at first glance. However when I zoom in very close, I start to see the two lines which are supposed to be exactly on top of each other coming apart. I am aware that I have to get really, really close, however I still don’t understand why this is occurring.
I am already working with very low numbers for the tolerances. My problem is not necessarily the tiny gap itself (althought I would love it if this would not be there at all…) but of course I fear that if I use the resulting surfaces for some other operations, the irregularity would spread and eventually multiply, so that at some point I end up with multiple lines not matching each other and as a result causing all kind of problems.
I ´ll attach a part of the file that illustrates what I am talking about:

split.3dm (356.4 KB)

thank you in advance for any feedback / help



Hi Andreas - the display will eventually not be precise enough if you zoom in forever. A better test is to Pull the split edge to the cylinder and check the pulled edge curve to the original edge with CrvDeviation:

Minimum deviation = 0
Maximum deviation = 7.1409e-14


Hi Pascal, thanks for your answer…
yes, I know at some point the elements in the display will start to “jump” …and I am aware that the distance is so small, that it is insignificant in the “real world”, however I still don’t understand why it is there at all…

My problem is often that I start to work on a complex object, over time I do a lot of trimming, sometimes even offsetting and so on. At some point the object gets messed up, I end up with several lines above each other that do not match and I am not talking about 7.1409e-14 but sometimes like a 1mm.

Of Course it might also be due to small errors that can occur during long revision processes when we change things over and over again, but I also fear that it might be related to these small “gaps” multiplying over time…

I already learned to be careful and use the original curves if possible because some operations seem to be destructible in the way that resulting edges often are altered and don’t resemble the same curve as the original one…

Is there some strategy to prevent this?

thanks again


Many operations are not (cannot be) exact - trimming surfaces is one, it is subject to the tolerance in the file.

Pulling/projecting curves is another of these.


thanks Pascal, I guess I´ll do a little reading…


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