[QGIS-trac] Re: [Quantum GIS] #2349: Data not displayed with on the fly projection

[Quantum GIS]

#2349: Data not displayed with on the fly projection
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   Reporter:  ccrook                            |              Owner:  nobody       
       Type:  bug                               |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.7.0
  Component:  Projection Support                |            Version:  Trunk        
   Keywords:  projection display                |   Platform_version:               
   Platform:  All                               |           Must_fix:  No           
Status_info:  0                                 |  
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Comment(by ccrook):

 Replying to [comment:4 rduivenvoorde]:

 > As soon als you pan the 180/-180 line out of the mapcanvas points are
 shown normally.
 >
 > Probably a dateline problem?

 I don't think this is a dateline problem.  Could test (but haven't yet) by
 creating a data set elsewhere that is spanning the central meridian of a
 TM projection (which I do think is the issue)

 My original observation (I suspect that this is due to incorrectly
 determining a bounding box for the data in the source data coordinate
 system when the data is being selected for display) is probably a bit
 cryptic

 What I think is the issue is that the bounding box for the view window is
 defined in terms of the canvas coordinate system.  I think this may be
 converted to the layer coordinate system by converting the coordinates of
 the extreme points of the bounding box.  However when the view extents are
 transformed to the layer coordinate system it is no longer a rectangle
 aligned with the coordinate axes.  So the transformed coordinates of the
 corners of the extents do not correspond to the corners of the bounding
 box of the transformed view extents.  What this means is that some points
 get incorrectly filtered out of the view based on the incorrectly
 transformed bounding box.

 Resolving this is a non-trivial problem!

-- 
Ticket URL: <http://trac.osgeo.org/qgis/ticket/2349#comment:6>
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