[QGIS-trac] Re: [Quantum GIS] #1716: improvements to ZoomLast, ZoomNext tools (extent history)

[Quantum GIS]

#1716: improvements to ZoomLast, ZoomNext tools (extent history)
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        Reporter:  smizuno           |         Owner:  mhugent      
            Type:  patch             |        Status:  new          
        Priority:  minor: annoyance  |     Milestone:  Version 1.4.0
       Component:  GUI               |       Version:  HEAD         
      Resolution:                    |      Keywords:               
Platform_version:                    |      Platform:  All          
        Must_fix:  No                |   Status_info:  0            
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Comment (by smizuno):

 Replying to [comment:8 marisn]:
 While I was only fixing the extent history mechanics to enable/disable the
 buttons and track the history correctly, I considered what happens when
 the map CRS is changed.

 While it would be a good idea to have the extent history track the map
 CRS, there are situations where a previous extent could 'blow up' a CRS
 transformation. This should be trapped so it doesn't cause a segfault, be
 what should QGIS behavior be in this case? Doing nothing is confusing.
 Popping an error dialog gets really annoying after the first one.

 The most common scenario I have seen is forgetting to set the map CRS
 before loading data that has a UTM projection, for example, after starting
 QGIS. In this case the extents are more correct for the UTM, not the
 default EPSG:4326, if the map CRS is now changed to UTM. The extents are
 likely way out of bounds, as well.

 I almost put a clear extent history on map CRS change, but decided not to
 because that behavior could be confusing and annoying.

 I believe that all consequences of map CRS change on the extent history
 should be considered before doing anything further.

-- 
Ticket URL: <http://trac.osgeo.org/qgis/ticket/1716#comment:9>
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