Civil 3D 2018 and Large Surfaces

Civil 3D 2018 and Large Surfaces

By Matt Kolberg, Application Specialist at SolidCAD 

If you have recently upgraded to Civil 3D 2017 or 2018 or are planning to AND you work with large surfaces (I’ll let you define what a large surface is) you’ll want to read this article!

If you want to skip past all the history and get to the point, the short story is, 2017 and 2018 store the entire surface definition within DREF drawings and this affects performance. This option can be turned off.

Most Civil 3D users know that a large surface should be created in one file and Data Referenced (DREF’d) to another file for use in such things as profiles and corridors. This helps reduce errors and improves performance.  2017 and  2018 are no different, but it contains a new feature which is meant to help another occasional user issue.

When DREFs were introduced they were, and still are, susceptible to the source file being moved. If the source file is moved, not unlike an AutoCAD XREF, the source object cannot be found and the DREF drawing is empty.

Civil 3D 2014 introduced a new feature where all Data References (except surfaces) are actually stored in the DREFd drawing file. If an alignment’s source DWG cannot be found, it’s no problem since the alignment actually lives in the DREFd file.  It’s still a DREF and it will still synchronize when the source file is found, but at least there’s something in the drawing and not a blank slate.  There is no option to turn this feature off, and you likely wouldn’t want to.

Surfaces were not included with this feature because they can be very large and performance would suffer in the DREF file. They weren’t included, that is, until Civil 3D 2017.  Entire surface definitions are now stored in DREF files.  If the source file is lost, you still have your surface.  This is great for drawings containing few or small surfaces, but it can drastically affect performance for large surfaces.

If your source surface is big enough to require an MMS file, there will be a second MMS file for the DREF drawing. These can be very large.  Not only does your drawing performance suffer, but now your hard disk must contain the additional MMS file.

This option is ON by default and I’d leave it there if you primarily work with smallish surfaces. I’d turn it off if you typically work with big ones.  There are two options:

  1. Change the setting in your template (DWT) so that future drawings will have the option set as you wish.
  2. Change the option afterward for drawings containing existing surface DREFs.

The DWT setting can be found in the Civil 3D Settings tab:

If a surface has already been DREF’d, the option can be changed in the Prospector:

2018 has been an excellent version and this feature is welcome to most, but beware of large surfaces.