[QGIS-trac] Re: [Quantum GIS] #1993: North arrow changes direction (with OTFR disabled and projected CRS) at very high/low zoom levels

[Quantum GIS]

#1993: North arrow changes direction (with OTFR disabled and projected CRS) at
very high/low zoom levels
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        Reporter:  vince               |         Owner:  homann       
            Type:  bug                 |        Status:  new          
        Priority:  minor: annoyance    |     Milestone:  Version 1.4.0
       Component:  Projection Support  |       Version:  1.3.0        
      Resolution:                      |      Keywords:  north arrow  
Platform_version:  10.6.1              |      Platform:  All          
        Must_fix:  No                  |   Status_info:  0            
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Changes (by lutra):

  * owner:  nobody => homann
  * platform:  OS X => All
  * summary:  North arrow points sometimes north, sometimes south => North
              arrow changes direction (with OTFR disabled and
              projected CRS) at very high/low zoom levels
  * component:  Map Legend => Projection Support
  * milestone:  => Version 1.4.0

Comment:

 I'm not really very deep into projections matters, so I may not be able to
 explain this correctly, and if I'm saying something wrong please correct
 me.

 Try add a layer defined in wgs84, for example a shape of the world
 borders: to let your France shape overlap the world borders you will need
 to enable OTFR. If you define wgs84 as project CRS, then you'll see
 obviously all aligned and the north points upwards, regardless the zoom
 level.

 Now change the project CRS to a projected system and zoom to your France
 layer, you'll obviously still see the north upwards, but then when you
 zoom out the north arrow will start change the direction because the world
 border layer "wraps". It seems to me that the direction changes depending
 on what you have in the centre of the canvas. ***

 I'm not sure why this also happens when you zoom in a lot, but I see that
 it happens when the scale reads "4 cm", so I guess that is not really
 important.

 I'm also not really sure why this happens with OTFR *not enabled* and the
 project defined with a *projected CRS*. Interestingly it seems to happen
 always when zooming in (a lot) regardless the projected crs, but I found
 that when zooming out with certain projected crs, the north arrow does not
 change direction. As I said I'm very scarce about this matters, so maybe
 there is a reason that makes perfect sense for this behaviour.

 ***
 Doing such test I found a bug that crashes qgis under ubuntu, but I will
 open a separate ticket.

-- 
Ticket URL: <https://trac.osgeo.org/qgis/ticket/1993#comment:4>
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