QGIS georeferencer: Thin Plate Spline (TPS) residual
1) Is anyone able to explain in simple manner what does mean error exactly mean? I use metric values, so suppose 3.64109 is expression of meters and "e" is mathematical constant: http://en.wikipedia.org/wiki/E_%28mathematical_constant%29 but what's next?
2) Why does image become more brighter after TPS transformation?
I work on archival aerial imagery and I'm testing all of the transformation types and re-sampling methods to find the best one. As you can anticipate, I'm not mathematician and I'd like to understand what's result of my work in fact.
Thin plate spline works perfectly for all GCP you have entered, but possibly not for the rest of the image.
If you use polynomial interpolation, you get residuals for all GCP points.
If one or several of your GCP have a low accuracy, the polynomial interpolation can compensate that, leaving the image as a whole with less distortion.
With TPS and one GCP offset, you get a nasty distortion around it, with no way to eliminate that than deleting the GCP. See this question for an example: Georeferencing an old map in QGIS using Thin Plate Spline