[Qgis-user] Wrong area count QGIS 3.20+?
Zoltan
zoltans at geograph.co.za
Mon Jan 3 06:51:38 PST 2022
Hi Bas,
Please say which version of ArcPro - I might be heading for these type
of issues in the next few months.
Thanks and regards,
Zoltan
On 2022-01-03 16:46, Sebastian Gutwein wrote:
> 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.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 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/
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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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--
=============================================
Zoltan Szecsei GPrGISc 0031
Director, Geograph (Pty) Ltd.
GIS and Photogrammetric Services
Cape Town, South Africa.
Mobile: +27-83-6004028 (Signal, not WhatsApp)
www.geograph.co.za
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