I am using RiverGIS plugin in QGIS and facing a problem in Extracting Manning's n values for cross-sections. The error code is as follow: -

Extracting Manning's n values for cross-sections UndefinedFunction('function st_line_interpolate_point(geometry, numeric) does not exist\nLINE 39: ST_Line_Interpolate_Point(inter_xs_dump.geom, 0.0000...\n ^\nHINT: No function matches the given name and argument types. You might need to add explicit type casts.\n') Process aborted!

I am not very expert in in coding, so please help me.

2 Answers 2


The error is apparently due to a change in the function name in PostGIS (several versions back...). If you're willing to do a trivial edit to one of the plugin python files, I think you'll be able to overcome this.

Find the plugin directory on your system, and open the file hecobjects.py with a simple text editor. At line 839, change the function name ST_Line_Interpolate_Point to: ST_LineInterpolatePoint. (Remove two underscores. No other changes)

Save and then retry the plugin.



I tried this tip. The plugin directory may be something like


I changed ST_Line_Interpolate_Point into ST_LineInterpolatePoint in hecobjects.py. Didn't work better. Then I encountered hecobjects.cpython-39.pyc. Don't know a damn about this file, its language and what it is for, but it has the same function ST_Line_Interpolate_Point. I changed it into ST_LineInterpolatePoint, got no results. Then I shut off QGIS and opened it again : yeeeh, it's ok !

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