Polyline Angle Issue

[J-Porter]

This may be an AutoCAD issue, but we're working in Civil 3D 2024.  We have two polylines at the intersection of a road.  If we check their angles they show 90 degrees.  We then offset them and the angles still show 90 degrees.  However, when we fillet the offset lines the angle is slightly off.  I made a video to better explain.  

[v-silvestre]

Hi Jason, I'm curious if this is a linework geometry error or a labeling error.  Could you verify if the angle of that filleted line is changing or is it just the something like the dimension having a rounding error?

I would test to by adding additional dimensions & C3D labels before you fillet your line if it really is changing your geometry:

Also, is it possible to upload a drawing?

[J-Porter]

Sorry, I meant to upload the drawing.  In one my previous tests I verified the bearings on the lines were exactly the same.  I've have also run an audit on the file and found no errors.  

Thank you for taking the time.  

[AllenJessup · Accepted solution]

A quick guess is that it looks like you're working in a high coordinate system. Polylines don't seem to like high coordinate systems. Autodesk would tell you to move them closer to 0,0. Got to go but if no solution by tomorrow. I'll look at the drawing

[v-silvestre]

Thanks for uploading the drawing.  After taking a look, it doesn't appear to be that the geometry is changing.  When I try to dimension the angle between the offset lines, they are still show as parallel.  As for the linear dimensions, the do not change either.  One thing I found is that if you use TRIM on the lines before using FILLET, the angle dimension stays correct.

As for what is the root cause of the dimension behaving this way, that's a great question for ADSK support.

[J-Porter]

@AllenJessup, you were correct.  I moved the linework closer to the origin and was able to edit the lines and get the same angle.  I'm not sure why this is so.  And, this is tough to swallow because we deal with projects millions of feet from 0,0. 

Thank you for your help,  

[AllenJessup]

@J-Porter I've been down that road with Autodesk before. I can't find the article I read years ago. But the gist of it was that the program works with a set number of places that are distributed on either side of the decimal point.  The more you have to the left of the decimal the less you have on the right. That can lead to small imperfections in the calculations.