[Qgis-user] Field Calculator calculates negative area

[Lene Fischer]

Hi Morten - Again
I made a Vector>Check Geometry validity.
There are 62 errors at your polydog, all intersections. This might give you a problem.

Regards
Lene Fischer
________________________________________
Fra: qgis-user-bounces at lists.osgeo.org [qgis-user-bounces at lists.osgeo.org] på vegne af magerlin [MAP at ramboll.dk]
Sendt: 25. marts 2013 16:07
Til: qgis-user at lists.osgeo.org
Emne: [Qgis-user] Field Calculator calculates negative area

Hi

I wanted to calculate the areas of some polygons and used the $area in the
field calculator.

But one of my (rather complicated) polygons ended up having a negative area.

As can be seen from the below screen shot the derived area from the identify
tool is correct (a least it is positive) while the value Areal which I
calculated is negative:

<http://osgeo-org.1560.n6.nabble.com/file/n5042754/Negative_Area.png>

A peculiar thing is that until I save my shape file the area is correct in
the field calculator (Area2 is no saved yet):

<http://osgeo-org.1560.n6.nabble.com/file/n5042754/Negative_Area2.png>

The shap file can be doanloaded here:  Storzoner.zip
<http://osgeo-org.1560.n6.nabble.com/file/n5042754/Storzoner.zip>

Also Version 1.9 calculates a negative value even thoug it firsts show up
when I close and reopen the attribute table.







-----
Regards Morten

Qgis 1.8.0 Stand alone installer in Win7 64 bit
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