Hi Jorge Tornero, Bernhard, Matthias, Nyall, All Thanks for taking up the scalebar issue.
I agree that in most cases, the scalebar is more of an academic / customary. It hardly gives a "true" measurement. Users generally use that as means of comparison and not to measure the exact distance. IMO, the scalebar makes sense when you have maps in large scales like 1:100 better. Otherwise, its just an estimation. Hope QGIS can provide a solution. Regards Ted On Fri, Jun 27, 2014 at 1:27 PM, Ted <tiruchirapa...@gmail.com> wrote: > 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.stro...@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.stro...@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 >>> >>> >>> >> >> __________ Information from ESET Mail Security, version of virus >> signature database 9997 (20140625) __________ >> >> >> The message was checked by ESET Mail Security. >> http://www.eset.com >> >> >> _______________________________________________ >> Qgis-developer mailing list >> Qgis-developer@lists.osgeo.org >> http://lists.osgeo.org/mailman/listinfo/qgis-developer >> > >
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