AutoCAD insertion scale units: what you need to know

Last updated: 2020-06-16

Background

AutoCAD 2017 and later includes the option to set the insertion scale units (INSUNITS variable) to "US Survey Feet". In prior versions, only "Feet" was available. By default, the WisDOT Civil 3D 2016 and Civil 3D 2018 templates are set to "Unitless". This prevents unintended shifts when using AutoCAD-based commands such as for inserting or Xreferencing drawings.

However, when a coordinate system is assigned, the INSUNITS variable is automatically changed to "Feet" for Civil 3D 2016 and "US Survey Feet" for Civil 3D 2018. This happens when App menu > Drawing Utilities > Drawing Settings > Units and Zones tab > Set AutoCAD variables to match: Checked

The WisDOT Civil 3D 2016 and Civil 3D 2018 configurations reset the INSUNITS variable back to "Unitless" the next time the drawing is opened.

Potential Issues

Tip: If you are using the WisDOT Civil 3D configurations, the potential for issues is very small. Since the WisDOT configuration forces INSUNITS to "unitless" each time a drawing is opened, AutoCAD does not do any scaling of units when inserting or Xreferencing drawings.

Here is one example scenario where there could be an issue:

  1. A drawing is created with Civil 3D 2016
  2. The Civil 3D 2016 drawing is assigned a coordinate system. (this changes the INSUNITS to "Feet")
  3. The Civil 3D 2016 drawing is not re-opened with the WisDOT configuration.
  4. A new drawing is created with Civil 3D 2018
  5. The Civil 3D 2018 drawing is assigned a coordinate system. (this changes the INSUNITS to "US Survey Feet")
  6. The Civil 3D 2018 drawing is not re-opened with the WisDOT configuration.
  7. The Civil 3D 2016 drawing is Xreferenced or inserted into the Civil 3D 2018 drawing.
  8. This will result in a shift in the data due to the "Feet" to "US Survey Feet" conversion.

Summary and Prevention

  1. Users should be mindful of the INSUNITS setting when working in Civil 3D to prevent any discrepancies when working with multiple drawings.
  2. When Xreferencing or inserting a drawing, both drawings must either have the same INSUNITS setting, or one of the drawings must have INSUNITS set to "Unitless".
  3. The INSUNITS variable only changes when you manually change it or when you assign a coordinate system with the "Set AutoCAD variables to match" box is checked.
  4. INSUNITS does not affect Civil 3D data shortcut referencing.
  5. If you are using the WisDOT configurations of Civil 3D, there are safeguards in place that force INSUNITS back to "Unitless" the next time a drawing is opened. If you are not using the WisDOT Civil 3D configurations, contact support.cae@dot.wi.gov for more information on how to force the INSUNITS variable to "Unitless" at drawing startup.
  6. Future versions of the WisDOT Civil 3D templates will not have the "Set AutoCAD variables to match" box checked in the drawing settings. This will add an additional safeguard by preventing INSUNITS from changing when a coordinate system is assigned.