[OSM-dev] OpenStreetMap Cartographic: A client-side rendered OpenStreetMap Carto
osm at imagico.de
Tue May 26 14:43:58 UTC 2020
On Tuesday 26 May 2020, ndrw6 at redhazel.co.uk wrote:
> Rasterization is a data generalization technique too.
No it isn't. Generalization is the most frequently abused term in
cartography. Calling ST_Simplify and way_area filtering on OSM
landcover polygon data generalization is a bit like calling JPEG
compression noise reduction.
But we are drifting off topic here.
> Yes, in some
> cases it leaves no artifacts at all
Who would say that? In fact sampling artefacts (a.k.a. aliasing) are
the mother of all artefacts in computer graphics.
The point is that sampling artefacts are very well understood and it is
known how to minimize them.
> I've been looking into the code and I couldn't find anything related
> to polygon generalization. Where is it done?
Lossy geometry compression is happening in ST_AsMVTGeom - which is not
just the inevitable coordinate rounding to the vector tile coordinate
grid but also the subjective choice of per feature Douglas-Peucker line
for the well argued suggestion not to do that. The way_area filtering
is explicit in the SQL code.
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