{"id":620,"date":"2026-10-31T13:43:43","date_gmt":"2026-10-31T13:43:43","guid":{"rendered":"https:\/\/blog.get-map.org\/?p=620"},"modified":"2026-10-31T13:43:43","modified_gmt":"2026-10-31T13:43:43","slug":"experimental-sea-map-overlay","status":"publish","type":"post","link":"https:\/\/blog.get-map.org\/index.php\/2026\/10\/31\/experimental-sea-map-overlay\/","title":{"rendered":"Experimental Sea Map Overlay"},"content":{"rendered":"\n

After way too many years in the making the Mapnik renderer is now finally able to draw circle arcs, with and without radius lines and textual labels. I had been trying to implement this several times over the years, but always got stuck on details like how to use the agg render backend — who’s author unfortunately as deceased and can’t be asked any more \ud83d\ude41

Now with a little help from a companion named Claude I was able to complete that work (minus some final touches), and the code got accepted into Mapnik now, so it will be in future Mapnik releases.

See also e.g. https:\/\/github.com\/mapnik\/mapnik\/pull\/4589

And with that the one missing piece that prevented me from offering an OpenSeaMap-like style for printing is now in place (OpenSeaMap always used their own home grown rendering solution instead of Mapnik \/ CartoCSS).

So I have no also started to build a full OpenSeaMap-lookalike overlay style using the new Mapnik ArcSymbolizer feature.

See also https:\/\/github.com\/hholzgra\/mapnik-seamap-overlay

I’m not fully done yet, there are still some aspects of the OpenSeaMap style missing, most importantly all buoys and beacons still miss their coloring and their top markers; only the base shapes are rendered for now.

But I’m making good progress, and hope to finish this by Christmas latest, so that we can offer to print finished OpenSeaMap-like maps for the first time on the 40C3 Chaos Communication Congress in Hamburg at the end of this year.

With the event happening near the largest German harbor this seems like the perfect occasion …. \ud83d\ude42

For now the SeaMap overlay style is already available on print.get-map.org, under “Special Interest” overlays, but still marked as experimental.<\/p>\n\n\n\n

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After way too many years in the making the Mapnik renderer is now finally able to draw circle arcs, with and without radius lines and textual labels. I had been trying to implement this several times over the years, but always got stuck on details like how to use the agg render backend — who’s … Continue reading “Experimental Sea Map Overlay”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2],"tags":[],"_links":{"self":[{"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/posts\/620"}],"collection":[{"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/comments?post=620"}],"version-history":[{"count":1,"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/posts\/620\/revisions"}],"predecessor-version":[{"id":622,"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/posts\/620\/revisions\/622"}],"wp:attachment":[{"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/media?parent=620"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/categories?post=620"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.get-map.org\/index.php\/wp-json\/wp\/v2\/tags?post=620"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}