Civil 3D Hydraflow Storm Sewers Import Coordinate Shift

When working with Civil 3D Hydraflow Storm Sewers, if you export an .stm file from Civil 3D and then subsequently make edits in the .stm file in Hydraflow and save the .stm file, you will find that the coordinates for the pipes and structures have shifted.  If working in feet, this shift may be only thousandths of a foot.  This can still be a problem since everything in Civil 3D is dynamically connected.  For example, this can change how your pipes and structures appear in your profile and section views.

Following is a figure showing the shift in coordinates.  On the left is the .stm file exported from Civil 3D.  On the right are the coordinates in the .stm file after it has been saved in Hydraflow.  Since the coordinates end up different, when working in Hydraflow, it’s a good idea to keep your original Civil 3D exported .stm files separate from the ones saved by Hydraflow.

When importing this .stm file back into Civil 3D and updating your pipe network, you will find that your structure and pipe locations have changed to the values in the .stm file.  As a workaround to this problem, we’ve created a utility that will generate an updated .stm file containing the correct coordinates from the original Civil 3D .stm file and the modifications from the Hydraflow .stm file.  Note that this application will not work if the number of pipes and structures in the two .stm files do not match.

You can download the application here.  This software is provided as-is. Use the following instructions to update the coordinates:

1. Extract the HydraflowCoordinateFix.exe file and run the program.
2. Select the Civil 3D .stm with the correct coordinate values (the one not saved by Hydraflow).
3. Select the Hydraflow .stm file, the one with your changes, but incorrect coordinates.
4. Select a new file to write to (as long as you don’t choose a file from steps 2 or 3, then it will not modify those files).
5. Click OK.
6. Import the new .stm file into Civil 3D.  It should apply your Hydraflow updates, but use the correct coordinates.