[QGIS-Developer] QGIS Georeferencer improvements

[Martin Dobias]

Hi Frank

On Wed, Apr 1, 2020 at 8:47 AM Frank Sokolic <sokolic at worldonline.co.za> wrote:
> >
> > B. map coordinates - that is what ArcGIS does. The image is placed at
> > some initial position in the map, picking of image coordinates and map
> > coordinates for GCPs is done in the same map canvas. (i.e. two clicks
> > in single map canvas)
> >
> > The option B has the advantage that it is quite easy/intuitive to have
> > live preview of the image transformation as GCPs are being added. With
> > option A the live preview of the transform is not really possible (we
> > are still in image coordinates) - and the preview would need to be in
> > a separate map canvas.
>
> While I like the live preview of option B, I find this option difficult
> to use when georeferencing the raw image against a raster dataset such
> as an aerial photograph. The top raster in the drawing order, e.g. the
> raw image, covers the bottom raster as the live image transformation
> proceeds, requiring the top raster to be toggled on/off when identifying
> GCPs. In this case I find the current dual window approach is better as
> the images can be placed side-by-side for easier identification of GCPs.

Yeah this case when georeferencing aerial imagery on top of other
aerial imagery is a valid concern. This could be possibly addressed by
having a switch (with a keyboard shortcut) that would toggle opacity
of the georeferenced layer to 0% and 100% (or some other values).

Another option would be to have an action to open a new map canvas
dock widget containing just the georeferenced layer (with live warp as
well) that could be either docked on the side of QGIS main window or
even moved to a second display. Closing this map canvas dock widget
would make the georeferenced layer appear again in the main map
canvas...

What do you think? In this way, with single canvas by default and with
optional "pop out" georeferencing canvas we could probably address the
issue nicely.

Regads
Martin