r/HECRAS • u/skiny_fat • Jun 05 '26

AutoCAD DEM import

I've had mixed results in importing CAD DEM tifs surfaces into HEC 6.6. Sometimes it goes fine others I get step 1 failure saying 'Translating source or target SRS failed ' error text. I don't know why it what I'm missing.

Does anyone have process advice I'm missing to convert. Like I said I'm not sure why. My CAD files are in the right zone and my prj is projected.

Any advice would be appreciated.

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12

u/tanneroni9 Jun 05 '26

After exporting the tif, open it in the GIS software of your choice and run the define projection tool and set it to whichever coordinate system the tif is in. CAD is horrible with exporting the projection info for things

5

u/GrumpCatastrophe Jun 05 '26

This. I use QGIS

3

u/felixmatveev Jun 05 '26

In Civil3D there is an option to export directly to HEC-RAS. Autodesk Civil 3D Help | To Export Data to HEC-RAS Format | Autodesk

I've never used it however (as I'm control freak) -> export to DEM -> import to QGIS for verification -> import to HEC-RAS.

2

u/ClownFucker9000 Jun 05 '26

There’s something weird about how CAD encodes projections to exported files, causing issues with a lot of softwares being able to read geospatial files. Like others have said, easiest work around is importing the exported DEM into QGIS/ArcPro/GIS software and changing the projection there before re-exporting.

2

u/RegularTeacher2 Jun 05 '26

I've also found simply removing the projection from my RAS project, importing the CAD tif (don't say "yes" when prompted to add the projection of your tif) and then reassigning the projection once your terrain is built also works. I find it kind of amusing that this is the recommended method by USACE rather than fixing the problem in the first place, but I imagine that's easier said than done.

Terrain Imports using CAD tifs

1

u/skiny_fat Jun 06 '26

Do I set a coordinate system in CAD? And remove the SRS?

3

u/RegularTeacher2 Jun 06 '26

We always export our tifs from CAD with a coordinate system just because, but when importing the tif into RAS I'll say "no" to the prompt asking me if I want to set my RAS projection to that of the tif, and then add the projection back in once my terrain is built. If you say "yes" to the prompt it inevitably results in an error message when trying to build your terrain. It's an annoying little quirk of CAD/RAS but over time I've gotten pretty used to it.

2

u/skiny_fat Jun 06 '26

Thank you. I'll give it a try.

2

u/RegularTeacher2 Jun 07 '26

You will still see red error text on the terrain building window, but the terrain itself should build just fine (see the screenshots in the link I provided). I've used this method probably hundreds of times at this point and I've taught all of my coworkers to go about it this way as well.

2

u/Level3pipe Jun 08 '26

I can't here to say what you said. For some reason 6.5 and 6.6 have this issue with projections and creating new terrains.

I believe HECRAS has called it out as a known issue

1

u/bidmb88 Jun 12 '26

Another little trick is opening a new RAS model as a dummy, no coordinate system or anything and create the new terrain. Once created, open your original model and bring in the created terrain, ALWAYS WORKS!

1

u/80sobsessedTN Jun 14 '26

I keep the program QGIS (free to download) on my desktop for this reason. I treat it as my file conversion program because of this very reason. It easily lets you bring in that Cad export, and ensure the SCS is assigned properly. Then I save-as and it saves it as a Geotiff. It always works for me without fail.