Question:

How are units defined for StormCAD for OpenRoads and Subsurface Utility Engineering?

Sometimes I see differences in the coordinates listed in the Utility Properties when compared with the Element Information Panel. Why is this?

Answer:

The Subsurface Utility tools in OpenRoads are a merger of technologies between traditional hydraulics products like StormCAd and Road/Site CAD based OpenRoads.

The units defined in the DGN Settings of OpenRoads will be most familiar to road and site designers.  The settings are accessed from Settings > Design File > Working Units.  Here, you define the units used in the CAD files.

The utility data is also stored in an embedded database which is a part of the technology of the hydraulics family of products which are also available in standalone versions.  Part of the enhanced capabilities available in these H&H products is an enhanced capability to change the units of displayed values on the fly. The top level location for setting units for display of the utility features in reports and such is accessed at Subsurface Utility > Project > Project Defaults > Units.

This dialog sets the units that are used for any new projects.  As such, these units should be defined in the hydraulic seed file, which is usually the utility feature definition library in your workspace.   These units should be set in the hydraulic seed file and be consistent with your DGN Units.  Thus, once set, you can operate normally without worrying with units if you so choose.

Please not that while importing any hydraulic model into SUDA (Subsurface Utility>Project>Import>Import .stsw), the imported model will have the SI units (hydraulic units), even if they are set to US customary units in the SewerGEMS, StormCAD etc.

However, as noted above, the units handling is a bit more robust for the utility features because of this units system which applies to the utility database.  For example, you can change display units on the fly from virtually every interface which shows values with units.  In the next image notice that I can change the units used to display time of concentration simply by right click and click on Units and Formatting.

An example of change in the units between the utility data units and the CAD units of .dgn file.

In these cases, you just need to change the either of the unit formats to match the values/units, by above mentioned methods..

For many values used for utilities, such as Tc, there is no CAD equivalent so there is no chance for confusion.  But, where things can get a little confused is when I change the units on the fly so that they are inconsistent with the DGN units.  This will be most confusing for large linear values measured in feet.  The most common introduced inconsistency is that the user is working in US Survey Foot units but the utility units have been set to International foot.  Then it appears that units shown in CAD are at odds with the units shown in Utility Properties.  You can rest assured that your data is safe, it is just being reported differently in the two places.  And the corrective action is also simple. Just right click as shown above and reset the utility display units appropriately.

Also notice above that the units being used are always shown in parentheses.  Thus Time of concentration has "(min)" next to it.  This will help guide you when seeming discrepancies are discovered. 

As noted above, this duplication of units tools is an artifact of the ongoing merger of technologies and can be expected to be consolidated in future versions.

See Also

communities.bentley.com/.../23850.setting-units-for-data-import-and-export-landxml-inroads-etc

communities.bentley.com/.../8169.changing-units-or-converting-units-for-elements