[postgis-devel] [PostGIS] #503: ST_Area on small polygons in EPSG:31467 gives incorrect results depending on 32-/64-system-architecture

[PostGIS]

#503: ST_Area on small polygons in EPSG:31467 gives incorrect results depending
on 32-/64-system-architecture
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  Reporter:  mjansen  |       Owner:  pramsey      
      Type:  defect   |      Status:  new          
  Priority:  medium   |   Milestone:  PostGIS 1.5.2
 Component:  postgis  |     Version:  1.5.X        
Resolution:           |    Keywords:               
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Comment (by nicklas):

 I'm sorry. I think I talk rubbish.

 But it is very strange. I calculated the two first polygons from above in
 a spreadsheet with the algoritm in the area function and I get to the
 result  0.001953125  !!!!

 And I get the same result for each step as the function.

 I think this is about rounding and extream polygons. The number of
 decimals in the coordinates is only 3 or 4 and the polygons seems to be
 very long and thin triangels. I couldn't get QGIS to draw anything else
 than a line for one of them.

 Can that be the answer?
 The precision of the koordinates is not enough to get a good answer from a
 polygon like this. Since it is so long and thin a very little different in
 coordinates mekes a very big difference in area if it affects the triangel
 to be thinner or fatter.

 A note
 I calculated the answer in the spreadsheet in an environment that gave the
 "right" answer in PostGIS and had the wrong answer in the speadsheet.

 So, I don't think it is a bug, it is just about floating point differnces
 in systems showing with extream plygons.

 Rubbish again???

 /Nicklas

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/503#comment:8>
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