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

[Johannes Kröger (WhereGroup)]

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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-- 
Johannes Kröger / GIS-Entwickler/-Berater

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