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

[Matthias Kuhn]

Hi Bernhard,

On 24.06.2014 11:06, Bernhard Ströbl wrote:
> Hi Matthias,
>
> probably this is academical...
>
> Am 24.06.2014 10:42, schrieb Matthias Kuhn:
>> Hi Bernhard,
>>
>> I wouldn't say no sense at all. It strongly depends on the context, but
>> if you have for example a lesson for geography students and are
>> introducing CRS/projections and their properties one could want to add a
>> scale bar in degrees.
>
> But would that scalebar show the degrees for lon or lat?

Maybe I am wrong, but I assume that there is no difference. One unit
(degree) will represent the same amount of pixels/points horizontal and
vertical.

> If the first (lon) for which latitude?
It doesn't matter in degrees. But it really matters when trying to put a
scalebar in meters.
> Either of the two: how do you want to tell people that this scalebar
> is only true for North-South (lat) or East-West (lon) measurements and
> must not be used in any other direction? IMHO a scale bar is to enable
> readers to use their ruler to measure a distance on the map in _any_
> direction.
>
>> I agree that it's not very common and most people
>> are probably unused, but if you explicitly state the fact that the map
>> is in degrees you might even avoid confusion and prevent people from
>> trying to compare distances.
>
> But adding a scale bar encourages users to compare distances! The fact
> that a map is suitable to measure and compare distances is not decided
> by the map units but by the used projection and the covered area. If
> your map is in degrees just enable the graticules and (if useful) add
> a scalebar in m/km/miles (does that work with degrees? I have not
> tried. If not this would be a feature request.)
>
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?

> BTW: for which point of a map is the scale bar currently created
> (thinking of non-distance-true projections and large areas e.g.
> continents)?
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.

Regards,
Matthias