Re: [Qgis-user] New Features in Shape Tools 3.2.0

classic Classic list List threaded Threaded
24 messages Options
12
Reply | Threaded
Open this post in threaded view
|

Re: [Qgis-user] New Features in Shape Tools 3.2.0

Nyall Dawson
On Mon, 1 Oct 2018 at 23:09, Helmut Kudrnovsky <[hidden email]> wrote:

>
> >I'm struggling to work out where the difference lies between the code
> >paths. Do you mind sharing the values from the st state struct when
> >G_ellipsoid_polygon_area is called for this polygon?
> >
> >Nyall
>
> delivered by Markus Metz, GRASS dev:
>
> st->AE: 40408299984661.4
> st->QA: 0.00446291999342754
> st->QB: 2.68888340714427e-05
> st->QC: 1.71432450253425e-07
> st->QbarA: -1.00448998025995
> st->QbarB: 0.0015057373196404
> st->QbarC: -5.48062628444059e-06
> st->QbarD: 2.44903500362035e-08
> st->Qp: 1.00448998025995
> st->E: 510065621153775
>
> precision: %.15g
>
> by adding a debug message in GRASS: in lib/gis/area_poly1.c add debug
> messages in G_begin_ellipsoid_polygon_area().

Thanks so much -- found the error now!

Nyall
_______________________________________________
QGIS-Developer mailing list
[hidden email]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Reply | Threaded
Open this post in threaded view
|

Re: [Qgis-user] New Features in Shape Tools 3.2.0

Nyall Dawson
In reply to this post by Helmut Kudrnovsky
On Mon, 1 Oct 2018 at 23:01, Helmut Kudrnovsky <[hidden email]> wrote:

>
> Helmut Kudrnovsky wrote
> >>[...]
> >>Caris LOTS: 14.737 km^2
> >>ArcMap:     14.727,446 km^2
> >>MapInfo:    14.727,352 km^2
> >>GeoMedia:   14.726,443 km^2
> >>Planimeter: 14.722,522 km^2
> >>QGIS 3.2:   14.652,181 km^2
> >>QGIS 2.8:   14.652,181 km^2
> >>[...]
> >>My suspicion is that the geodesic algorithm used by QGIS (and apparently
> > GRASS) is to blame here.
> >
> > a quick check in GRASS 7.7.svn shows :-)
> >
> > |m2|km2|
> > |14718097678,673|14.718,097679|

Ok, with https://github.com/qgis/QGIS/pull/8090 QGIS now exactly
matches GRASS' value (14.718 km2).

(For reference -- not a regression, this bug has been around since
ellipsoidal calculations were introduced to QGIS!)

Nyall
_______________________________________________
QGIS-Developer mailing list
[hidden email]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Reply | Threaded
Open this post in threaded view
|

Re: [Qgis-user] New Features in Shape Tools 3.2.0

pcav
Hi all,

thanks a lot for this. It's a beautiful example of how open source
works, finding and solving problems through collaboration and highly
skilled people. It would be nice if someone would write about this for a
wider audience.

All the best.


Il 10/02/2018 05:12 AM, Nyall Dawson ha scritto:

> On Mon, 1 Oct 2018 at 23:01, Helmut Kudrnovsky <[hidden email]> wrote:
>> Helmut Kudrnovsky wrote
>>>> [...]
>>>> Caris LOTS: 14.737 km^2
>>>> ArcMap:     14.727,446 km^2
>>>> MapInfo:    14.727,352 km^2
>>>> GeoMedia:   14.726,443 km^2
>>>> Planimeter: 14.722,522 km^2
>>>> QGIS 3.2:   14.652,181 km^2
>>>> QGIS 2.8:   14.652,181 km^2
>>>> [...]
>>>> My suspicion is that the geodesic algorithm used by QGIS (and apparently
>>> GRASS) is to blame here.
>>>
>>> a quick check in GRASS 7.7.svn shows :-)
>>>
>>> |m2|km2|
>>> |14718097678,673|14.718,097679|
> Ok, with https://github.com/qgis/QGIS/pull/8090 QGIS now exactly
> matches GRASS' value (14.718 km2).
>
> (For reference -- not a regression, this bug has been around since
> ellipsoidal calculations were introduced to QGIS!)
>
> Nyall
> _______________________________________________
> QGIS-Developer mailing list
> [hidden email]
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer

--
Paolo Cavallini - www.faunalia.eu
QGIS.ORG Chair:
http://planet.qgis.org/planet/user/28/tag/qgis%20board/

_______________________________________________
QGIS-Developer mailing list
[hidden email]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Reply | Threaded
Open this post in threaded view
|

Re: [Qgis-user] New Features in Shape Tools 3.2.0

C Hamilton
In reply to this post by Nyall Dawson
Nyall,

Thanks so much for investigating and fixing this. Also thank you all who have contributed to this discussion. This was an important bug to find and fix. I think we will find that the geographiclib calculations are going to be slightly more accurate coming in at 14.737 km^2, but the GRASS calculations are quite accurate.

Calvin


On Mon, Oct 1, 2018 at 11:12 PM Nyall Dawson <[hidden email]> wrote:
On Mon, 1 Oct 2018 at 23:01, Helmut Kudrnovsky <[hidden email]> wrote:
>
> Helmut Kudrnovsky wrote
> >>[...]
> >>Caris LOTS: 14.737 km^2
> >>ArcMap:     14.727,446 km^2
> >>MapInfo:    14.727,352 km^2
> >>GeoMedia:   14.726,443 km^2
> >>Planimeter: 14.722,522 km^2
> >>QGIS 3.2:   14.652,181 km^2
> >>QGIS 2.8:   14.652,181 km^2
> >>[...]
> >>My suspicion is that the geodesic algorithm used by QGIS (and apparently
> > GRASS) is to blame here.
> >
> > a quick check in GRASS 7.7.svn shows :-)
> >
> > |m2|km2|
> > |14718097678,673|14.718,097679|

Ok, with https://github.com/qgis/QGIS/pull/8090 QGIS now exactly
matches GRASS' value (14.718 km2).

(For reference -- not a regression, this bug has been around since
ellipsoidal calculations were introduced to QGIS!)

Nyall

_______________________________________________
QGIS-Developer mailing list
[hidden email]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
12