[QGIS-Developer] QGIS Georeferencer improvements

[Frank Sokolic]

Hi Martin,

On 2020/03/31 23:26, Martin Dobias wrote:
> Hi Nyall
>
> On Fri, Mar 13, 2020 at 8:45 PM Nyall Dawson <nyall.dawson at gmail.com> wrote:
>> On Sat, 14 Mar 2020 at 01:13, 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?)
>> I would personally prefer the second option. I think a significant
>> amount of users doing regular georeferencing would have dual screen
>> setups (or large screens) and would appreciate having the a larger
>> georeferencer window then a dock would allow.
> I have been thinking about this and what are the pros and cons of
> having a separate window for georeferencing vs doing georeferencing in
> main map canvas. Actually rather than discussing whether to have one
> or two windows, the key bit to decide on is something else - what
> would be the coordinate system of the georeferencer canvas:
>
> A. image coordinates - that is what we have in QGIS georeferencer now:
> the image gets loaded without any distortion and stays that way all
> the time. Picking of map coordinates for GCPs has to be done in a
> separate map canvas. (i.e. one click in "georeferencer canvas", and
> one click in "reference map canvas")
>
> 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.

>
> So where I am hesitating is whether to stick to option A which is
> probably familiar to QGIS users - or with option B that may provide
> better UX thanks to the live update of the warped raster (or vector).
> I guess we will need to choose one or the other - supporting both
> options would be probably too confusing. I am trying to figure out
> which way to take, because this will also have great impact on the
> workflow on how GCPs would be picked on the map(s) using map tools...
>
> Thanks for your thoughts :-)
>
> Cheers
> Martin
> _______________________________________________

Regards, Frank.