[Qgis-developer] Derived Area is calculated wrong

Maciej Sieczka tutey at o2.pl
Tue Aug 8 13:26:52 EDT 2006


Hi,

(I'm reposting this, as my first attempt was filtered out by anti-spam
and on the second attempt, forwarded by Tim, nobody replied.)

This is a serious issue. Is it a bug or user/setup problem?

There is a vector polygon Grass layer. It's area is, according to
'v.to.db option=area units=k', 32281.680484. Also d.what.vect reports
"area size: 32281680484.380993". These seem correct, as after
rasterising it in Grass at 10m resolution the raster non-null area
(r.stats -a) is very close: 32281681800.000000.

However, querying the same vector exported to shapefile (v.out.ogr
type=area) in QGIS 0.8 (current SVN) returns '(Derived) Area 32303.759
km2'. It's 22 km2 more!

Querying the polygon Grass vector itself in QGIS returns the same wrong
derived area too.

The more complicated shape, the bigger the difference.

Could somemebody investigate? The shapefile is attached.

Maciek

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