[Qgis-developer] QGIS Crash - Serious problem in 2x

[Matthias Kuhn]

Hi Jorge

On 24.06.2014 14:34, Jorge Tornero - Listas wrote:
> Hello All,
>
> El 24/06/14 14:02, Matthias Kuhn escribió:
>> Doesn't really make sense to me. Graticules are just another
>> reference for distances (in degrees in this case) and an alternative
>> or addition to scale bars. What problem exactly would the combination
>> of a grid in degrees and a scalebar in meters solve?
>
> Well, you should try to think about people which may receive
> positioning info in degrees but need to judge distances in "real
> world" units: on ships, for instance (sorry but that's my
> bussiness...). And remember, always taking into account that the area
> should be relatively small.
... and close enough to the equator to have no horizontal/vertical
length mismatch problems.
In this case (comparing distances in real-world units) another
projection should actually be preferred. Putting the degrees-grid on top
of that in turn sounds very sensible.
>
> Grid in degrees --> Fast  positioning in the map.
> Scale in whichever units but degrees --> Fast estimation of distances,
> travel times, speeds.
>
> Of course you shouldn't trust this kinds of map to navigate... but for
> practical uses (survey planning (up to some extent), quick info,
> simple illustration) they are OK and appreciated.
>
>> No idea.But if there should be proper support for scalebars in meters
>> on degree-based maps, then it has to be configurable. And also the
>> two different scalebars (horizontal vs. vertical) that you mentioned.
>> Then it could be that there is a small enough area that this can be
>> considered accurate enough to be useful. And there should be warnings
>> to inform the mapper that he might be misleading readers and should
>> consider to reproject.
>
> To tell you the truth, in the actual state of the scalebar, all this
> is sort of tricky. It would be great to have it properly implemented,
> as you suggest. But maybe this maps are seldom used by the majority of
> QGIS users and it is not worth the effort and it may perfectly stay as
> a trick.

Thinking about it. A warning for unsuitable scale bars would be a nice
feature. That could be the shown if the scale varies by more than a
certain threshold over the map. I expect that this would help a lot of
people to even be aware of the risk involved when choosing projections
and to make a conscious decision.

Regards,
Matthias