[QGIS-Developer] QGIS Georeferencer improvements

Luigi Pirelli luipir at gmail.com
Sat Mar 14 02:14:23 PDT 2020


On Fri, 13 Mar 2020 at 16:13, Martin Dobias <wonder.sk at gmail.com> wrote:

> 1. Georeferencer opens in a new window. In order to see the main map
> canvas and the georeferenced layer side by side, it is necessary to do
> some resizing of windows which is inconvenient. It would be maybe more
> practical to have the georeferenced image in a dock widget in the main
> window - and all georeferencer related map tools included in the main
> QGIS window as well. (Or maybe the other way around - to keep
> georeferencer as a separate window, but allow the main map canvas to
> be embedded in it?)

se j rectifier plugin

> 2. Georeferencer is a plugin. Its core/gui functionality cannot be
> reused elsewhere. It would be useful to have some Processing
> algorithms to load/save GCPs, to extract GCPs to raster images, to
> save GCPs to raster images and to warp imagery according to GCPs (and
> chosen transformation method).

yes please

> 3. Georeferencer does not allow live preview of how the georeferenced
> raster image would end up looking on the map - user is required to
> write warped image to disk as a new file and only then see the
> results. It should be possible to use the estimated transformation
> based on GCPs and show the layer in the main map canvas any time (if
> wanted).

see j rectifier plugin

4. It uses a combination of GDAL-based transformation methods
> (Polynomial of 1st/2nd/3rd order, thin plate spline) and some of its
> own (Helmert, Projective), for which it also requires GSL library as a
> dependency. In my opinion, QGIS georeferencer should leave all the
> math to GDAL which does a great job there. Moreover, I have some
> doubts about the methods that do not come from GDAL: the “Helmert”
> method is simply 2D affine transform (offset+scale+angle), while true
> Helmert transformation is 3D transformation with 7 parameters. Do we
> need it if GDAL’s 1st order polynomial transformation should do just
> that? And the “Projective” method which is a bit of a mystery to me.
> First of all, I am not sure in what situation it is useful and the
> documentation only says it is “a linear rotation and translation of
> coordinates” - which is a bit vague. It looks like a subset of RPC
> method supported by GDAL (although GDAL does not have estimation of
> RPC coefficients). Overall I would be for removal of these methods and
> stick to what GDAL offers.

+1 to all in gdal... btw seems gdal has some hidden or poorly documented
features. e.g geoid and gcp seems (form documentation) mutually exclusive,
but they are not (reading the code) and can be combined to reach better

> Martin


Luigi Pirelli

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