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

Tue Jan 4 11:44:43 PST 2022

Happy to help!

On Tue, Jan 4, 2022 at 2:04 PM Sadowski Jarosław <jaroslaw.sadowski at cpk.pl>
wrote:

> Dear Sebastian,
>
>
>
> I am very grateful to you for taking on my case in such depth.
>
> Now everything is clear to me, thank you kindly for your answer.
>
> I will spread this knowledge further on local QGIS community and Polish
> internet QGIS forums.
>
>
>
> with best regards
>
> and greetings to the entire community of this amazing open-source project
>
> 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
>
> *From:* Sebastian Gutwein <bas at rdgland.com>
> *Sent:* Monday, January 3, 2022 3:47 PM
> *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>
>
> 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
> <!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.
>
> 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%7C72f10e545ec748e873ca08d9cec7e6d0%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637768180240837962%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=n9NfD1jSBsKsrD9ujGf50us0H5McoNOnjZTet%2BvXFlo%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%7C72f10e545ec748e873ca08d9cec7e6d0%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637768180240837962%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=7md2NSCR87fR2Uhv2tMwrisF9%2FbiulNQH%2BuTPwqCqok%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%7C72f10e545ec748e873ca08d9cec7e6d0%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637768180240837962%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=I7pSrQ9eHBnY%2BOq6xN5BTbUV2ZkcJOP0k30teMLdJUk%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%7C72f10e545ec748e873ca08d9cec7e6d0%7Cfa798250ca0b4a1bb47381cff4a1752b%7C1%7C0%7C637768180240837962%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=AcHBFAywXe35DZ3kZWTRk%2FuaUEp145TjOwmJKp7sf64%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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