[Qgis-user] Wrong area count QGIS 3.20+?

[Sebastian Gutwein]

Ok to add to the fun I tried the calculations in ArcPro and interestingly
if I run it using calculate field with this expression
*!shape.geodesicArea at hectares!* I get the QGIS 3.22 value of 31271112 but
if I run Geoprossessing Add Geometry Attributes I get the QGIS 3.16 value
of 31271108.
[image: image.png]
So if you want them to match I guess you should use the python expression
in ArcGIS Pro!

I guess we are back to the old adage of All Measuring is Guessing.
-Bas




On Mon, Jan 3, 2022 at 8:43 AM Sebastian Gutwein <bas at rdgland.com> wrote:

> Yes that was my read as well except previously it was the Grass method and
> now it is Geographic Lib method because that is theoretically more accurate
> and is the same method that is used in Postgis and other places. The
> switched happened because someone noticed the difference between QGIS’s
> calculations and Postgis’s calculations. If I am reading the pull requests
> correctly even Grass has switched to the Geographic Lib method. I’m
> surprised that ArcGIS Pro uses the same method as the Grass method.
>
> On Mon, Jan 3, 2022 at 2:57 AM Sadowski Jarosław <jaroslaw.sadowski at cpk.pl>
> wrote:
>
>> Sebastian,
>>
>>
>>
>> thank you very much for your precise answer and materials sent - I have
>> read them carefully.
>>
>>
>>
>> So, as far as I can understand, QGIS has moved in version 3.20 to a new
>> way of counting areas (other libraries? GRASS algorithm instead of
>> Geographic lib? I have actually noticed a different nomenclature and
>> definition of EPSG 2180 for some time in new versions…), that will be more
>> accurate?
>>
>>
>>
>> I must admit that, for me as a GIS operator, it is surprising and sounds
>> like bad news - so far surfaces have always been the same in various GIS
>> software, whether or not it was open-source or commercial (ArcGIS Pro). So
>> from this moment it will be that I will get different surfaces depending on
>> the software it was calculated? :(
>>
>> with kind regards
>> JS
>>
>> *_____________________________*
>>
>> *Jarosław Sadowski*
>> Ekspert ds. Baz Danych i Analiz Przestrzennych | *Biuro Strategii i
>> Planowania, Projektowania i Inżynierii Podprogramu Kolejowego*
>> *Database and Spatial Analysis Expert |Railway Subprogramme Strategy &
>> Planning, Design & Engineering Department*
>> e: jaroslaw.sadowski at cpk.pl
>>
>> *From:* Sebastian Gutwein <bas at rdgland.com>
>> *Sent:* Saturday, January 1, 2022 7:13 AM
>> *To:* Sadowski Jarosław <jaroslaw.sadowski at cpk.pl>
>> *Cc:* qgis-user at lists.osgeo.org
>> *Subject:* Re: [Qgis-user] Wrong area count QGIS 3.20+?
>>
>>
>>
>> Nie otrzymujesz często wiadomości e-mail z adresu bas at rdgland.com. Dowiedz
>> się, dlaczego jest to ważne
>> <http://aka.ms/LearnAboutSenderIdentification>
>>
>> There was some discussion on this in the list serve back in January
>> <https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.osgeo.org%2Fpipermail%2Fqgis-user%2F2021-January%2F047638.html&data=04%7C01%7Cjaroslaw.sadowski%40cpk.pl%7Cf7cc24b07b7c42e8902a08d9ccedca61%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637766145287655707%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=bUHOuswrG6tPdkebzFYem%2BVsSrgjFhbSLVcKCiu6TW0%3D&reserved=0>
>> that resulted in this feature request
>> <https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fqgis%2FQGIS%2Fissues%2F40888&data=04%7C01%7Cjaroslaw.sadowski%40cpk.pl%7Cf7cc24b07b7c42e8902a08d9ccedca61%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637766145287655707%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=dY89NsDscjybmwQPMV9PjPOwckPlcv%2B8TEWjl69rTtM%3D&reserved=0>
>> and this pull request
>> <https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fqgis%2FQGIS%2Fpull%2F41726&data=04%7C01%7Cjaroslaw.sadowski%40cpk.pl%7Cf7cc24b07b7c42e8902a08d9ccedca61%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637766145287655707%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=IRMFsaJYT7xpylDJCZNvXAUNzdmtTjNbI4VyQMKtedE%3D&reserved=0>.
>> I tested your polygon, to the best of my limited ability, and the areas
>> were indeed different in QGIS 3.16 and 3.22 as would be expected from that
>> change . However it would be hoped that the area measurement would be more
>> accurate in 3.22.
>>
>>
>>
>>
>>
>> On Fri, Dec 31, 2021 at 6:49 AM Sadowski Jarosław <
>> jaroslaw.sadowski at cpk.pl> wrote:
>>
>> Dear all,
>>
>>
>>
>> I am asking for help with QGIS error/bug or verification of proper usage
>> of basic QGIS functionality “$area”.
>>
>> From version 3.20 upwards, it counts areas differently than before (3.18
>> calculated area is different than 3.20). Up to version 3.18 everything was
>> fine, equal to calculations from ArcGIS Pro (geodesic mode).
>>
>> Anyone have an idea where the differences come from?
>> This is example vector [image: Ikona zip] PL_2180.zip
>> <https://eur06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcpkonline-my.sharepoint.com%2F%3Au%3A%2Fg%2Fpersonal%2Fjaroslaw_sadowski_cpk_pl%2FEVs0-TiEvPdBjMaqXrEvGfoBI0VussbJaYHdDVFfQnEYug%3Fe%3DVDY3rf-&data=04%7C01%7Cjaroslaw.sadowski%40cpk.pl%7Cf7cc24b07b7c42e8902a08d9ccedca61%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637766145287655707%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=JlPtyjeeYHQxV0DdlGrsPwjTNy9FHqqyEqEpLNrian8%3D&reserved=0>:
>> Polish borders in EPSG: 2180, in the table of attributes you can see the
>> areas (hectares) calculated for different versions of the software.
>>
>>
>>
>> with wishes for more success in the new year
>>
>> Jarosław Sadowski
>>
>>
>>
>> *_________________________________*
>>
>> *Jarosław Sadowski*
>> Ekspert ds. Baz Danych i Analiz Przestrzennych | *Biuro Strategii i
>> Planowania, Projektowania i Inżynierii Podprogramu Kolejowego*
>> *Database and Spatial Analysis Expert | Railway Subprogramme Strategy &
>> Planning, Design & Engineering Department*
>> e: jaroslaw.sadowski at cpk.pl
>> m: +48 532 720 230
>>
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> Sent from a phone. Amazing! But possibly garbled. Sebastian Gutwein
> Regenerative Design Group 1 Chevalier Ave Greenfield MA Bas at rdgland.com
> (631) 241-1018
>
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