[Qgis-user] Georeference DSM files in QGIS Using Georeferencer

[Greg Troxel]

Mark C Quilter via QGIS-User <qgis-user at lists.osgeo.org> writes:

> We flew the same site last month and produced orthomosaic, point cloud, and
> DSM.  However, we were not able to put out ground control so we needed  to
> rectify the images in QGIS so they would align with the 20213 imagery and
> models.  We were able to align the orthomosaic using Georeferencer (
> 3.28.2).  We have not been able to rectify the DSM.
>
> To attempt to rectify the DSM we used the same control points as used for
> the orthomosaic (the surface model was aligned with the orthomosaic).  This
> produces a file but its location was out of the mapping area and the
> elevation data was no longer correct.  We also used the 4 corners of the
> DSM for the control points in Georeferencer (these corners are the same
> corner extents as the rectified orthomosaic.  This also produced a geotiff
> somewhere on earth with no elevation data.

You didn't explain what file formats the DEM and DSM are in.  I wonder
if you can preprocess them to tiff and then use the georeferencer.

I am guessing you are working in NAD83 2011 (epoch 2010.0) either UTM or
SPC as both project CRS and output CRS for all of your georeferencing.

You might look at the data in the output files and try to understand
it.  tiffinfo will show you the scale and the UL point.   As I
understand it there is a hard norm that the tiff is oriented with the y
axis towards grid north for the CRS it is in.
In a map I georeferenced I see tags

  33550: xscale scale 0
  33922: 0, 0, 0,  UL-east UL-northing, 0

or at least that's what think.