[Qgis-developer] Saving map config, or the meaning of extent (again)

[Martin Dobias]

Hi Sandro

On Tue, Dec 2, 2014 at 11:15 PM, Sandro Santilli <strk at keybit.net> wrote:
>
> I'm still thinking that the triplet center,scale,rotation would be the
> simplest to retain. The problem with that is that keeping the scale
> might result in a different area being exposed depending on the
> output size. On the other hand keeping the extent would result in
> a different scale being used depending on output size.

Keeping just center+scale+rotation in QgsMapSettings seems like a
cleaner solution. Having to worry about various kinds of extent with
rotation in place will wear out our brains ("requested" extent,
"visible" extent, rotated "visible" extent). With your proposed
triplet we could at least get rid of the "requested" extent. (I still
find it a bit difficult to explain why both requested / visible extent
are needed - which is not a good sign!)


> What's more worth saving: scale of visible area ?

IMHO it does not really matter much.

One issue I could see by saving center+scale instead of extent is that
e.g. if you load a project with map extent to the whole project, in
differently shaped QGIS window some bits of data may be slightly
outside of the view. But even for this case the canvas could store its
original


Regards
Martin