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

[Quantum GIS]

#1219: Measure  tools and Identify (derived area, line) 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             
      Resolution:                                    |      Keywords:  measure area line
Platform_version:                                    |      Platform:  All              
        Must_fix:  No                                |   Status_info:  0                
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Comment (by smizuno):

 Replying to [comment:2 msieczka]:
 > Can you reproduce that with shapefiles? If so, please attach a sample
 Shapefile. Also please tell what target CRS should be defined when OTFR is
 enabled.

 Shapefiles also show the problem. see attached file

 The source files are in EPSG:26915 (UTM zone 15 NAD83)

 1m_100m_lines.shp - 4 lines: 2 of 1M length, 1 at diagonal (1.414M
 length), 1 of 100M length

 1m_100m_squares.shp - 2  squares: 1 of 1M on a side, 1 of 100M on a side

 The test uses EPSG:26915 as the map CRS, so there should be no difference
 in the length, area measurements.

 using Identify:

 Without OTF the squares measure (in Derived item) 1.000 m2 and 10,000.000
 m2
 Without OTF the lines measure (in Derived item) 1.000 m, 1.414 m (the
 diagonal) and 100.000 m

 With OTF enabled the squares measure 0.004 m2 and 1.046 ha
 Without OTF the lines measure 1.002 m, 1.417 m (the diagonal) and 100.208
 m

 Using the measure tools and trying to trace exactly the various shapes
 gets within a very small fraction of the expected values when OTF is off;
 there are significant differences with OTF on.

 I have also tried GRS80 as the ellipsoid for distance calculations, no
 difference.

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/1219#comment:3>
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