[QGIS-trac] [Quantum GIS] #1219: Measure Area tool and Identify(derived area) report incorrect values when On-The-Fly projection is enabled

[Quantum GIS]

#1219: Measure Area tool and Identify(derived area) report incorrect values when
On-The-Fly projection is enabled
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   Reporter:  smizuno                           |              Owner:  nobody       
       Type:  bug                               |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.0.0
  Component:  MapCanvas                         |            Version:  HEAD         
   Keywords:  measure area                      |   Platform_version:               
   Platform:  All                               |           Must_fix:  No           
Status_info:  0                                 |  
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 Occurs on Windows and Linux - don't know about Mac.

 Project CRS set to epsg:32615 or 26915 (haven't tried others), measures in
 meters; PostGIS layer in same CRS. Ellipsoid for distance measurements is
 WGS84.

 I created two squares, 1 meter and 100 meters on a side, and located at
 500000, 5000000.

 With OTF turned OFF Identify reports derived area of 1.000 m2, 10000.000
 m2 respectively. These are the expected values. Using the Measure Area
 tool to measure the squares gives reasonable values (variation due to
 drawing accuracy).

 Linux: With OTF turned ON Identify reports derived area of 5.740 ha, 1.046
 ha respectively. These are incorrect, especially for the 1m square.

 Windows: With OTF turned ON Identify reports derived area of 0.004 m2,
 1.046 ha respectively. These are incorrect, especially for the 1m square.

 With OTF turned ON, the area reported using the Measure Area tool drawing
 on the squares are similar, with the 1m showing wildly varying values -
 very small to quite large (several ha) depending on how the area was
 drawn. The area reported also varies with the location the squares are
 positioned at.

 I have tested with actual dataset (a Minnesota county set) and find that
 the discrepancies are present but fairly small as the objects get larger.

 Mandriva Linux x86_64: r9037, GEOS 3.0.0, PROJ 4.6.0
 Windows XP: r9044, GEOS 3.0.0, PROJ 4.6.0

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/1219>
Quantum GIS <http://qgis.org>
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