I have a large port site (1200’ x 400’) that is fairly flat, and I have 1600 georeferenced drone shots. When I run an initial alignment, the model looks pretty good, but on close inspection, everything is slightly tilted.
So, using a GIS app (Global Mapper) with some okay orthophotography and terrain data, I made 6 ground control points across the site. I loaded them to RC and tied them to 5 or 6 photos each and everything looked good – the points all shoed up in the model where they should with minimal error.
But when I re-ran the alignment, I got a nightmare model where everything was tilted up into the sky…
Why would the GCPs show up in the right places but then cause the alignment to blow up?
It is possible that there are some issues with image priors (mostly altitude) and when RC tries to optimize with both georeferenced images and GCPs after the initial alignment it is causing the issue you are experiencing. Hard to say without knowing the details, but if you are confident with the GCPs I recommend you do the following:
After placing the control points in the first calculated component and before re-aligning, select all the images, and in the 1Ds view → Select inputs panel → Prior pose → Absolute pose and switch it to Unknown.
If you are confident with both image georeferencing and GCPs, after placing the GCPs in the component, keep the Absolute pose set to Position but this time delete the existing component or any other small components you might have so there is no existing alignment in the project. And now Align again.
I hope this helps and let me know if this helped you. Cheers!
Jakub,
Thanks very much for the suggestions!
The first time I tried deleting the components and setting Prior Pose/Absolute Pose to Unknown and re-aligning I got “pretzel world”. I almost gave up. The next time, I left Prior Pose on Position, deleted the components and it quickly solved the model.
-Donald
