Re: [Qgis-user] Simplify geometry - snap to grid

[Patrick Dunford via Qgis-user]

Is this the grid you see in View -> Decorations -> Grid ?

On 29/06/22 07:50, Delaz J via Qgis-user wrote:

Hi Klaus,

Just a guess: the only snap to grid thing I know about is 
https://docs.qgis.org/3.22/en/docs/user_manual/working_with_vector/editing_geometry_attributes.html#snapping-on-custom-grid. 
Worth a check?


Regards,

Harrissou

Le 28/06/2022 à 15:54, Klaus Mithöfer via Qgis-user a écrit :

hello,

with the simplify tool in QGIS you can simplify geometries using 
either  Douglas-Peucker Algorithm, Visvalingam-Algorithm or snap to 
grid. I understand the algorithms, but how the grid snapping work? 
Where is is the grid defined? I don't get that point. maybe someone 
can explain.


Thanks an kind regards
Klaus
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Re: [Qgis-user] Simplify geometry - snap to grid

[Andrea Giudiceandrea via Qgis-user]

*Klaus Mithöfer*
/Tue Jun 28 06:54:55 PDT 2022/

how the grid snapping work?


Hi Klaus,
the QgsMapToPixelSimplifier Class [1] gives a hint about what the 
"Simplify" algorithm "Snap to grid" method do:



SnapToGrid  

The simplification uses a grid (similar to ST_SnapToGrid) to remove 
duplicate points.




The code used for the "Snap to grid" method is at [2].

Another algorithm that snaps the vertex to a grid is the "Snap points to 
grid" [3], but this doesn't actually simplify the geometries, just 
simplifies the coordinates of the geometries.


Regards.

Andrea Giudiceandrea


[1] 
https://api.qgis.org/api/3.22/classQgsMapToPixelSimplifier.html#a0b97d82a3abd0876ce529ba9d9cfd412
[2] 
https://github.com/qgis/QGIS/blob/e113457133fe5d7c3f5e3b90a2795b8b691ae269/src/core/qgsmaptopixelgeometrysimplifier.cpp#L183-L229
[3] 
https://docs.qgis.org/3.22/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html?highlight=simplify#snap-points-to-grid 
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Re: [Qgis-user] Simplify geometry - snap to grid

[Delaz J via Qgis-user]

Hi Klaus,

Just a guess: the only snap to grid thing I know about is 
https://docs.qgis.org/3.22/en/docs/user_manual/working_with_vector/editing_geometry_attributes.html#snapping-on-custom-grid. 
Worth a check?


Regards,

Harrissou

Le 28/06/2022 à 15:54, Klaus Mithöfer via Qgis-user a écrit :

hello,

with the simplify tool in QGIS you can simplify geometries using 
either  Douglas-Peucker Algorithm, Visvalingam-Algorithm or snap to 
grid. I understand the algorithms, but how the grid snapping work? 
Where is is the grid defined? I don't get that point. maybe someone 
can explain.


Thanks an kind regards
Klaus
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Re: [Qgis-user] Own processing scripts doesn't load into processing toolbox since QGIS update to 3.22.8.

[Andrea Giudiceandrea via Qgis-user]

*Wolfgang Meinolf*
/Tue Jun 28 09:08:19 PDT 2022/

Hi,
Yesterday I updated my QGIS from 3.22.7 to 3.22.8. Since I have the issue, that 
two of my processing scripts don't load. As reason the log shows critical 
messages:


Hi Wolfgang,
it seems to me the same issue previously reported at 
https://trac.osgeo.org/osgeo4w/ticket/688, which has been fixed at that 
time but it occurs now again.


Regards.

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[Qgis-user] Own processing scripts doesn't load into processing toolbox since QGIS update to 3.22.8.

[Wolfgang Meinolf via Qgis-user]

Hi,
Yesterday I updated my QGIS from 3.22.7 to 3.22.8. Since I have the issue, that 
two of my processing scripts don't load. As reason the log shows critical 
messages:

2022-06-28T17:02:03 CRITICALKonnte Skriptalgorithmus 
xx.py' importieren [Translates: Could import 
Scriptalgorithmus. I think, it means Could NOT import script alg]
 DLL load failed while importing ogrext: Das angegebene Modul wurde 
nicht gefunden. [Translates: module not found]
2022-06-28T17:02:03 CRITICALKonnte Skriptalgorithmus y.py' 
importieren
 partially initialized module 'fiona' has no attribute '_loading' 
(most likely due to a circular import)


I found some older cases in the web where this was caused due to different 
versions of python library or wrong path to py libs.

Has anyone else observed such effect? If not I tend to open a case.

Thanks and best regards form bavaria


smime.p7s
Description: S/MIME cryptographic signature
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[Qgis-user] Simplify geometry - snap to grid

[Klaus Mithöfer via Qgis-user]

hello,

with the simplify tool in QGIS you can simplify geometries using either 
 Douglas-Peucker Algorithm, Visvalingam-Algorithm or snap to grid. I 
understand the algorithms, but how the grid snapping work? Where is is 
the grid defined? I don't get that point. maybe someone can explain.


Thanks an kind regards
Klaus
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[Qgis-user] QGIS 3.22 and 3.26 3D window is black

[Randal Hale via Qgis-user]

I think this is relating to a known Issue 
(https://github.com/qgis/QGIS/issues/40324) - but I wanted to check to 
see if anyone had  a thought.


I've got a Lenovo Laptop with an integrated Nvidia Quadro P2000. If you 
do anything involving 3D the window is black in 3.22 and 3.26. With some 
effort sometimes I can get it to "blue" but nothing displays. No 3D. 
It's not a data issue - seems to be a video driver (I think).


I was wondering if anyone had experienced this and possibly had a fix. 
My gut says I need to do something with the Nvidia Control Panel and 
make some adjustments. I'm not 100% sure on what to change.


Anyway - any help is appreciated.

Randy

--
-
Randal Hale
rjh...@northrivergeographic.com
https://www.northrivergeographic.com

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Re: [Qgis-user] how to simplify polygons without loosing too much information

[Michael.Dodd via Qgis-user]

Thanks very much for the responses.

One of the key features I am after is that any method does not ‘loose’ chunks 
of the polygon, does not matter too much if a few extra bits are included but 
if they are lost this is more of a problem. Looking through the 3 main methods 
it is not clear (to me at least) if they can be asked to avoid too much loss of 
this sort. In the third suggested url below the ‘best’ method does actually 
loose quite a chunk of a headland and in my case headlands like this are places 
where some of the more interesting points are likely to be.

I want to make sure dots within the polygon are included and it does not matter 
too much if some extra ones are included but it does matter more if some are 
lost.


From: Qgis-user  On Behalf Of Johannes 
Kröger (WhereGroup) via Qgis-user
Sent: Monday, June 27, 2022 3:58 PM
To: qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] how to simplify polygons without loosing too much 
information


CAUTION: This mail comes from outside the University. Please consider this 
before opening attachments, clicking links, or acting on the content.

Hey Michael,

the algorithms involved are Douglas-Peucker and Visvalingam. With those terms 
you might find some nice explanations and guidance online. Some quick links:

- 
http://bl.ocks.org/msbarry/9152218
- 
https://dulldrums.github.io/polygon-reduction-algorithms-demo/
- 
https://ignf.github.io/CartAGen/docs/algorithms/line/visvalingam.html

For your use case (keeping the overall shape) I would try Visvalingam first as 
that is pretty much its goal too.

Cheers, Hannes


Am 27.06.22 um 16:52 schrieb Michael.Dodd via Qgis-user:
I know there are various simplify tools in qgis but perhaps I don’t understand 
how to use them best. I want to simplify i.e. reduce the number of nodes in a 
polygon without changing the overall shape too much for country or similar 
outlines.  When I have tried this the simplify tends to chop off bits that a 
human doing a manual simplification would not, in some areas the simplification 
could loose loads of nodes whereas in other areas it needs to keep more of them 
or the overall shape will be greatly changed. Is there anyway round this or am 
I asking for something that is not logical?



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