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

[Richard McDonnell]

Hi All,
It appears that, when you georeference an image which already contains reference information it in effect applies a shift to the outputs.
One solution might be one of the options suggested here<https://gis.stackexchange.com/questions/237314/removing-coordinate-system-but-not-coordinates-of-raster>. The one which looks best suited for Georeferencing data wich already has a CRS applied, would appear to me to be..

gdal_translate -co PROFILE=BASELINE -co TFW=YES dem.tif dem_clean.tif

It seems to reset the GeoTiff back to just a Tiff, from there you should be able to georeference it easy enough.
Hope that helps!
Kind Regards,

Richard




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Richard McDonnell MSc GIS, FME Certified Professional
FRM Data Management

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MSc GIS, FME Certified Professional

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Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36
Jonathan Swift Street, Trim, Co Meath, C15 NX36
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From: QGIS-User <qgis-user-bounces at lists.osgeo.org> On Behalf Of Michael Dufty via QGIS-User
Sent: 28 July 2023 03:16
To: Mark C Quilter <mcqqov at gmail.com>; qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Georeference DSM files in QGIS Using Georeferencer

I had similar issues in 2021 trying to use the georeferencer on tiff files that already had a crs assigned.
I did not resolve it at the time, just found a workaround, I wonder if it is still the same issue.
Seemed like QGIS was picking up the control points in the image as spatial coordinates, then treating them as pixel coordinates (or vice versa).

Alexis RL on this list said a proposed fix was up, but I never tested it.


From: QGIS-User <qgis-user-bounces at lists.osgeo.org<mailto:qgis-user-bounces at lists.osgeo.org>> On Behalf Of Mark C Quilter via QGIS-User
Sent: Friday, July 28, 2023 2:23 AM
To: qgis-user at lists.osgeo.org<mailto:qgis-user at lists.osgeo.org>
Cc: Mark Quilter <mquilter at utah.gov<mailto:mquilter at utah.gov>>
Subject: [Qgis-user] Georeference DSM files in QGIS Using Georeferencer


I am trying to measure the amount of sediment captured in several analog beaver dams on a small wash in northern Utah.

We flew the site with a drone and collected images that provided us with an orthomosaic, point cloud, and DSM (digital surface model) of the wash.  Ground control points were put out and the images and elevation models came into QGIS accurately (no rectification was needed).  This flight was before the analog beaver dams were installed (2021).

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.

We also used the plugin Freehand Raster Georeferencer by using the 2 point method (1 point being the LL corner and the second point being the UR corner.  The rectified orthomosaic that was produced the same time the DSM was made was used as the base map.  Again the produced file (png) was somewhere on earth but not in the correct location and the elevation data was corrupt.

I would appreciate and help with rectifying DEM and DSM files.

Thanks

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