I have the impression that writing SVG that it’s actually rendered by mapnik is quite hard. Let me show you my latest frustrating failed attempt:
I have my own fork of osm-carto, and I want to render a green hatching pattern on Natural Reserves and National Parks. So I took the patterns/military_red_hatch.svg file, loaded it in InkScape, changed the hatching color from #ff5555 to #55ff55, and saved it as patterns/np_nr_green_hatch.svg.
On the CartoCSS side, I added this code which is also a ‘clone’ of the military red hatch code:
line-width: 2;
}
}
+
+ // ::fill already exists in a previous branch, and seems like either
+ // `carto` and/or mapnik get confused by this
+ ::fill_2 {
+ // polygon-fill: #55ff55;
+ // polygon-opacity: 0.08;
+ polygon-pattern-file: url('patterns/np_nr_green_hatch.svg');
+ polygon-pattern-alignment: global;
+ }
}
}
}
to the #protectted-areas layer. This (of course?) didn’t work. mapnik (actually kosmtik) loads the project fine (and I even compile the thing into MapnikXML to double check), but I get no green hatching. Notice the commented out code; I used this to make sure this is being rendered.
Remembering that InkScape does not always write ‘good SVGs’ (I wish I could point to some discussion mentioning this), I instead openes the original SVG with a text editor, changed the color and saved as above. And it didn’t work either. We’re talking about the same actual contents of the original file with only 4 bytes changed.
Finally, I thought it was a mapnik bug, having a polygon pattern only attachment not rendering, so I instead added the pattern to the ::narrowline attachment:
[zoom >= 12] {
line-width: 2;
}
+
+ polygon-pattern-file: url('patterns/np_nr_green_hatch.svg');
+ polygon-pattern-alignment: global;
}
}
}
This didn’t render either. I have the impression this is not the first time I get frustrated trying to produce SVGs that mapnik accepts and renders. As a last resort, I copied the military file onto the other one and retried. Nothing.
So, is it my SVGs, InkScape, my CartoCSS, mapnik or any combination of those to blame here?
3 posts - 2 participants
Ce sujet de discussion accompagne la publication sur https://community.openstreetmap.org/t/care-to-share-your-knowledge-about-svg-and-mapnik/99281