[Qgis-developer] Wrong Area for large polygons in vector/Geometry Tools/Export/Add Geometry Columns

[Agustin Lobo]

ok, it seems there are 2 issues here:
1. The wrong results I get with
vector/Geometry Tools/Export/Add Geometry Columns
that are just missing digits to the right for large numbers

Giovanni: which version are you using?

2. The fact that results provided by R are so different. The most
intriguing/worrying is
that the R results are using package sp and package Rgeos.
I'm dealing with Edzer Pebesma regarding this issue in R-sig-geo and
will keep the list
informed. Perhaps I will open a new ticket on this specific subject
but lets wait
to see what Edzer says.

Agus



El día 9 de abril de 2012 14:35, Giovanni Manghi
<giovanni.manghi at gmail.com> escribió:
>
>> Check, for example, polygons with ID 25967 and 26570: according to the table,
>> the areas are
>> 25967: 8550196769
>> 26570: 1736474738
>>
>> while visual inspection indicates that 26570 is obviously much larger.
>
>
> this depends on
>
> http://hub.qgis.org/issues/4955
>
> if you compute areas (with both the filed calculator or the "add
> geometry columns tool") you get
>
> ID Area_FC
> 25967 8550196769.93
> 26570 173647473841.47
>
> that makes sense according to the size of polygons
>
>
>
>> Both results are different than those calculated by R:
>>
>> 25967:    9294889613
>> 26570: 205414657947
>>
>> Discrepancies with R are particularly large for polygons with area > 1E+10
>
>
> Can't understand these differences.
>
>
> -- Giovanni --
>
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