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#1 2020-06-16 11:15:42

James787
Member
Registered: 2020-06-16
Posts: 11

Remove woodland graphics beneath an area of Water

Hi

If i place an area of water (like a pong or lake) over woodland, the woodland graphics show through beneath the water.
Is there a way to remove the background woodland graphics beneath the water to stop them showing through?

Thanks

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#2 2020-06-16 12:59:01

kocio
Administrator
From: Warszawa
Registered: 2013-09-04
Posts: 3,482
Website

Re: Remove woodland graphics beneath an area of Water

Could you paste an example link and image showing this problem?

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#3 2020-06-16 21:12:50

SK53
Member
Registered: 2009-01-11
Posts: 656

Re: Remove woodland graphics beneath an area of Water

This is a known artifact from the way in which the symbology of trees is overlaid on the green base colour of the wood. The various decisions made when introducing the overlay are documented extensively on github.

In most cases the solution, which is probably correct for many purposes is to make the water area an inner member of a multipolygon with the original wood polygon as the outer. (This isn't perfect because it makes it harder to find lakes & ponds in a wood, but meets most use cases).

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#4 2020-06-17 09:08:10

BCNorwich
Member
From: Norwich, Norfolk, UK
Registered: 2010-07-31
Posts: 160

Re: Remove woodland graphics beneath an area of Water

Hi James787, If this is the area you are concerned about (https://tinyurl.com/y8bc9pn8), then you need to add the overall forest area into a nested multipolygon. Please see here https://tinyurl.com/y8yzaow3

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#5 2021-10-15 18:35:20

38446
Member
Registered: 2015-08-17
Posts: 7

Re: Remove woodland graphics beneath an area of Water

Yes, this isn't perfect, is it? I wonder if it isn't really that the issue of rendering should be addressed because really smaller ponds in the forest are in fact part of the forest and are even covered by the leaves of the trees. Isn't it tagging for the renderer to use multipolygons for these cases? Like in former times the layer tag was used.

SK53 wrote:

This is a known artifact from the way in which the symbology of trees is overlaid on the green base colour of the wood. The various decisions made when introducing the overlay are documented extensively on github.

In most cases the solution, which is probably correct for many purposes is to make the water area an inner member of a multipolygon with the original wood polygon as the outer. (This isn't perfect because it makes it harder to find lakes & ponds in a wood, but meets most use cases).

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#6 2021-10-15 21:21:44

SK53
Member
Registered: 2009-01-11
Posts: 656

Re: Remove woodland graphics beneath an area of Water

Yes in these cases it does not make sense to make them inners (closed canopy is a useful rule of thumb). The technical problem lies deep in Mapnik (the decoration has to be at a different level to the colour fill), and at the time it was regarded as a minor deficiency which we could live with (particularly as large bodies of water/grass etc are better represented by excluding them from the woodland, and the artefact of trees over a pond can be regarded as a positive as it shows closed canopy).

Most of these issues can be resolved if one does post-processing of polygons, but the main Carto-CSS map on the website has to be able to update in near real-time, so always uses polygons as is.

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