DSM file (Geo.tiff) won't import as a surface

[Anonymous]

Hello,

Thank you in advance for your help! 

I'm having trouble creating a surface out of a Digital Surface Model. My data is from a UAS survey.

When I try "Create surface from DEM..." in response I get "Unable to read file", and when try to just create a generic surface and then add the .tif file to the "DEM Files", I get "invalid DEM file".

This DSM Geo.tiff file is visible in QGIS. I've attached an image of it with Hillshade on. My first guess is that the file size is just too large and I have to compress it somehow (3GB file), but even when I try to import a much smaller cropped version of the .tif file (7MB) into Civil 3D, the same error messages pop up. 

Has anyone had a similar issue? 

Thanks again, 

Malcolm

Full view in QGIS:

Zoomed in detail in QGIS: 

[Kyle-L]

Would be be able to share a small cropped portion of the tiff?

Also, is the tiff in geographic coordinates (lat lon) or in grid coordinates (xy in feet/meters)? If it is geographic try exporting it out of QGIS in the coordinate system you are working in in Civil 3D. My guess is it might be a projection issue, but that is only a guess.

[ChicagoLooper]

Try not to crop an irregular shape. Crop a small rectangular or square portion, then use it as your surface definition. 

[Anonymous]

I've attached a rectangular cropped version of the original .tif file, it shows one of the culverts under the road. 

I'm not sure what coordinates the file is in, but under properties the units are set to meters: 

Also when I created this cropped version I think QGIS also created a .wld file that I wasn't able to attach.

I will try exporting the .tif file to the same coordinate system I am using in Civil 3D once I figure out what coordinate system it is already in. Thank you both! 

[ChicagoLooper · Accepted solution]

Manchester? Winthrop? Somewhere over there.

The DEM's metadata reveals the coodinate system is EPSG 32619 - WGS84 / UTM zone 19N - Projected.

This means the DEM is referenced against WGS84 datum. It is a projected coordinate system in Zone 19, Northern Hemisphere of the UTM grid and has units of meters.

To create your surface, go to Toolspace and create a new surface. For the surface definition, add your DEM. When browsing to your the DEM, change files of type to Geotiff. You don't need a world file for Geotiff. If the Geotiff was created (or clipped) correctly, the georeference will be built-in to the image itself and not be a spearate file.

There are two coordinate systems you are concerned with: (a) the native CS of the DEM itself and (b) the coordinate system you have already assigned to modelspace.

Your setup should look like image-1. Notice that while the DEM has a native CS of UTM-meters, modelspace has Maine State Plane West-feet. It's entirely OK for the DEM and modelspace to have differenct CS's b/c AutoCad will transform the DEM's coordinates to 'fit' your drawing environment. I'm guessing you want your drwing to be in feet and not meters.

Image-1.

If you create your surface correctly, you'll get this (image-2). If you have assigned State Plane CS to Maine NAD83, West Zone, feet, then you can draw in feet (not meters) while in modelspace.

Image-2.

The key to this exercise is to understand two coordinate systems are vital and the interplay of those coordinate systems on the DEM and on modelspace.

Note: If your DEM is a very big irregular shape and is giving you problems, a possible solution is to 'clip' the DEM to a square or rectangle. You can clip a little or clip a lot, it's up to you. Although AutoCad can work with irregular shaped DEMs, it doesn't always like them. It does better with squares or rectangles. 

[Anonymous]

Yes exactly, in Readfield!

Thank you for this excellent explanation. On my end everything works as you said after changing the DEM file's native coordinate systems when I import it, and while leaving the model space's coordinate system in the desired units (US foot).

Thanks again! This will work really well for my project. I will try and import a larger portion of the original DSM file and go from there.

- Malcolm