[gdal-dev] [EXT] Re: [Doc] gdal_calc.py extent option

[Matt.Wilkie]

To my mind the outputs of Union should be the largest extent area and Intersect is the smallest extent area. However any explanation in words alone will always have some ambiguity. It can't be avoided.

Union and Intersect via Wiki.GIS.com (I do find the intersect diagram less clear in this example than the next one):
[http://wiki.gis.com/wiki/images/thumb/2/28/Union.jpg/300px-Union.jpg]
[http://wiki.gis.com/wiki/images/thumb/4/4e/Demo_one.JPG/300px-Demo_one.JPG]

Union and Intersect in Wikipedia polygon theory:

[cid:image005.gif at 01D8E2CC.BDA0FE00]


http://wiki.gis.com/wiki/index.php/Union
https://en.wikipedia.org/wiki/Boolean_operations_on_polygons

-Matt

From: gdal-dev <gdal-dev-bounces at lists.osgeo.org> On Behalf Of Idan Miara
Sent: October 17, 2022 1:55 AM
To: Nicolas Godet <nicolas.godet at outlook.fr>
Cc: Andrew C Aitchison <andrew at aitchison.me.uk>; gdal-dev at lists.osgeo.org
Subject: [EXT] Re: [gdal-dev] [Doc] gdal_calc.py extent option

Hi!
I needed the docs are correct but as this is the second time it confuses people maybe the wording should be revised?

https://github.com/OSGeo/gdal/pull/5969<https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FOSGeo%2Fgdal%2Fpull%2F5969&data=05%7C01%7CMatt.Wilkie%40yukon.ca%7C8ec9f2c95b7c485d163508dab01d7941%7C98f515313973490abb70195aa264a2bc%7C0%7C0%7C638015937908111424%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&sdata=qgiJYx5KjebSDNQrw4QJHhY%2FrntE1Pyxfn32x31xlus%3D&reserved=0>

Any ideas?

On Mon, 17 Oct 2022, 11:49 Nicolas Godet, <nicolas.godet at outlook.fr<mailto:nicolas.godet at outlook.fr>> wrote:
Indeed, this is right.
My bad..
________________________________
De : Andrew C Aitchison <andrew at aitchison.me.uk<mailto:andrew at aitchison.me.uk>>
Envoyé : lundi 17 octobre 2022 10:25
À : Nicolas Godet <nicolas.godet at outlook.fr<mailto:nicolas.godet at outlook.fr>>
Cc : gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org> <gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org>>
Objet : Re: [gdal-dev] [Doc] gdal_calc.py extent option

On Mon, 17 Oct 2022, Nicolas Godet wrote:

> Dear Devs,
>
> In documentation<https://gdal.org/programs/gdal_calc.html#cmdoption-extent<https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgdal.org%2Fprograms%2Fgdal_calc.html%23cmdoption-extent&data=05%7C01%7CMatt.Wilkie%40yukon.ca%7C8ec9f2c95b7c485d163508dab01d7941%7C98f515313973490abb70195aa264a2bc%7C0%7C0%7C638015937908111424%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&sdata=ZQebVL1FblaUBIaZBYBsXHNJ0JfFm4nO8RzK2Gp4TZE%3D&reserved=0>>, extent param description seems a bit odd to me.
>
>
> union - the extent (bounds) of the output will be the minimal
> rectangle that contains all the input extents.
>
> intersect - the extent (bounds) of the output will be the maximal
> rectangle that is contained in all the input extents.
>
> Shouldn't it be the other way around?

I think this *is* the right way round;
"all" can be misunderstood but I can not think of a clearer phrasing,
although "every one of" might help.

> As I intend to add this option to QGIS gdal_calc window (very useful
> option), I must be sure.

--
Andrew C. Aitchison                      Kendal, UK
                    andrew at aitchison.me.uk<mailto:andrew at aitchison.me.uk>
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