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

Mon Jan 3 07:32:53 PST 2022

Looks like ArcGIS Pro 2.62.

On Mon, Jan 3, 2022 at 10:21 AM Zoltan <zoltans at geograph.co.za> wrote:

> 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: 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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>
> --
>
> =============================================
> 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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