CAD Drawing Units vs. C3D Toolspace > Drawing Settings > Units and Zone, Drawing Units

[Joshua7812]

Summary of my question:

Should our AutoCAD Drawing Units be set to be Unitless, Feet, or US Survey Feet? Our C3D Toolspace > Drawing Settings > Units and Zone, Drawing Units are set to Feet (the only options there, of course, being Feet and Meters); I believe our field crews' data collectors are set to US Survey Feet.

Some context, for information/discussion:

At the land surveying company I work for, it's recently come up whether our AutoCAD Drawing Units should be Unitless, Feet, or US Survey Feet—one of the other survey companies near us, whom we keep in frequent contact with, says they prefer using Unitless. My question/concern is how this setting works in relationship to the C3D Toolspace > Drawing Settings > Units and Zone, Drawing Units, as the only options there are Feet and Meters.

Prior to using C3D, we had our AutoCAD Drawing Units set to Unitless. After switching to C3D and setting Toolspace > Drawing Settings > Units and Zone, Drawing Units to Feet, our CAD manager at the time changed our AutoCAD Drawing Units to Feet, as well. Our data collectors for the field are set to US Survey Feet, I believe, and recently our calc guy imported the field crew's ASCII file and it was off (from his calculated linework) horizontally by about 5' he said. After he changed our AutoCAD Drawing Units from Feet to US Survey Feet, the data he imported landed in the correct spot, in relationship to his calculated linework.

I apologize if this is a dumb question. Myself and our calc guy were thrown into our roles a few years ago with little to no training in C3D because those in the roles left abruptly. We've learned everything as we've gone—mostly by trial and error, watching YouTube videos, and a lot of hands-on work in the software. Unfortunately, nothing like this has come up before for us to realize there was something here that we needed to gain an understanding of, regarding how these settings (C3D Toolspace > DWG Settings > Units and Zone, DWG Units vs. CAD DWG Units) function in relationship to one another. Thank you for any help you can be!

[tcorey · Accepted solution]

It is important to note that you aren't just offered Feet or Meters. Depending on which State Plane Coordinate Zone your assign your drawing, you are assigned US Survey Feet, International Feet or Meters. This is important at zone coordinates, often in the millions, making a very small difference in measurement of a foot into a big difference when times a million and more. 

Those other AutoCAD settings are for when drawings that might be set to different units are inserted herein. Also, have you had any angular input issues using Civil 3D? If so, set your angles to Decimal Degrees in AutoCAD Units dialog.

[AllenJessup · Accepted solution]

I usually say don't touch the AutoCAD units. That dialog should be eliminated from Civil 3D.

This is how the units are set OOTB and that's how I leave them. Changes can affect Civil 3D calculations.

The Drawing Setting from the Toolspace are what control the drawing. You'll notice that you don't have a Drawing Units option for US Survey Feet. That's controlled through your Coordinate System Selection.

[Joshua7812]

Thank you for your help. No, I haven't had any angular input issues. I'll keep that in mind though.

[Joshua7812]

Thank you for your reply. It was very helpful and informative, and it did help clarify things for me.