[Qgis-user] inconsistenty when calculating area depending on file type or projection?

[Carlos Cerdán]

And light was done!

Objective: to get planimetric-UTM-my-zone areas, in square Km, from a
LatLong layer, just at one step: in Fields calculator

area( transform( $geometry,'EPSG:4326', 'EPSG:32717' ))/1000000

Sorry, I was wrong for years, reprojecting layers; deactivating OTF SRC;
and using $area function: It happens when you don't read help in front of
you and don't try "new" functions.

Carlos


2016-10-19 15:11 GMT-05:00 Carlos Cerdán <sig.upagu at gmail.com>:

>
> > Under project properties, general tab - change "ellipsoid" to "None
> /Planimetric".
>
> Done, but calculated area is still... geodetic area?. I've tried ArcGIS
> and, for my GEO layer, It gives me desired area (same as an UTM layer,
> calculated with OTF off); so, it's me or QGIS, but I can't do this task in
> one step on QGIS: first I've to reproject mi GEO layer into an UTM one;
> disable OTF and finally calculate area (planar, as UTM is) in the new UTM
> layer.
>
>
> Carlos🤔
>
>
>
>
> 2016-10-18 19:58 GMT-05:00 Nyall Dawson <nyall.dawson at gmail.com>:
>
>> On 19 October 2016 at 02:22, Carlos Cerdán <sig.upagu at gmail.com> wrote:
>> > It was my fault. I was used to consider plane areas as "correct",
>> forgetting
>> > ellipsoidal areas. So, QGIS give us freedom to calculate planar or
>> > ellipsoidal (geodetical) areas, but we must be careful about settings;
>> Is
>> > not it?. Sometimes, too much freedom is annoying!
>> >
>> > But, How can I calculate UTM (planar) area from a GEO layer in one step?
>>
>> Under project properties, general tab - change "ellipsoid" to "None /
>> Planimetric".
>>
>> I keep meaning to split up the concept of ellipsoidal measurement from
>> OTF reprojection. In my view these are two different concepts - one is
>> just about display of data, the other relates to measurement. Ie, you
>> should be able to perform ellipsoidal calculations even if OTF
>> rendering is disabled.
>>
>> I just keep forgetting to do it early in a release cycle for extensive
>> testing...
>>
>> Nyall
>>
>>
>>
>
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