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

[Ted]

Hi Richard, Matthias, All

Yes, the crash problem is gone in master (nightly built) version. Thanks a
lot for the fix.  Tested it on Win 7 x64 and also Win XP x32.

Just for note, that issue is reported in v2.0.1 and v2.2 releases.

Will wait for the v2.4 release in July.


Regards
Ted





On Wed, Jun 25, 2014 at 5:02 PM, Bernhard Ströbl <bernhard.stroebl at jena.de>
wrote:

> Hi Nyall,
>
> thanks for clarification!
> However I would say that even if using a projected coordinate system (map
> units m) scalebars are not neccessarily accurate all over the map: if your
> map covers a small area this may hold true but not if you look at
> continents.
>
> Bernhard
>
> Am 25.06.2014 00:13, schrieb Nyall Dawson:
>
>  On 25 June 2014 01:20, Bernhard Ströbl <bernhard.stroebl at jena.de> wrote:
>>
>>  It does also matter in degrees, depending on the projection. same in
>>>>> meters: 1 cm on the map represents always a certain distance in
>>>>> reality (though this distance varies troughout the map depending on
>>>>> the projection and the area covered). If you look at the Lambert map,
>>>>> you realize that the distance between two parallels (10 degrees!)
>>>>> increases towards the pole, although in reality it is always (10*110km
>>>>> =) 1100 km. In the WGS84 map the distance between the parallels is
>>>>> constant but so is the distance between the meridians, but this is
>>>>> false as the distance gets less towards the pole in reality. So a
>>>>> scalebar (in m) being accurate in the middle of the map becomes less
>>>>> accurate towards the edges. Hence my question on which base the
>>>>> scalebar is calculated.
>>>>>
>>>>
>>>>
>>>> The question absolutely makes sense but I don't know the answer :)
>>>>
>>>
>>>
>>> Could you check? or whom would we have to ask?
>>>
>>
>> It's calculated this way:
>>
>> If you're working in a projected coordinate system (ie, map units are
>> metres):
>>
>> - Take the current extent of the map, calculate the width (x max - x
>> min), divide this by the width on paper of the map
>>
>> If you're working in a geographic coordinate system (ie, map units are
>> degrees):
>>
>> - Convert the width of the map (map's extent x max - x min) from
>> degrees to metres, using a variant of the Haversine formula, and
>> treating the current latitude as the MIDDLE LATITUDE from the map's
>> extent
>> - Convert this distance to a scale by dividing by the width on paper of
>> the map
>>
>> So, yes, scalebars using m/km/miles/etc are only an approximation when
>> map units are degrees, and are very inaccurate when used with maps
>> covering a large area or for areas far from the equator.
>>
>> Nyall
>>
>>
>>
>
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