[OSM-dev] OpenStreetMap Cartographic: A client-side rendered OpenStreetMap Carto

ndrw6 at redhazel.co.uk ndrw6 at redhazel.co.uk
Tue May 26 13:46:54 UTC 2020

On 26/05/2020 13:26, Christoph Hormann wrote:
> As Joseph has hinted when it comes to accurate rendering for precise
> mapper feedback without unintentional incentives at the lower zoom
> levels there are other options based on pre-rasterizing the data which
> would still allow using the benefits of client side styling.  I have
> demonstrated that in the past.

Rasterization is a data generalization technique too. Yes, in some cases 
it leaves no artifacts at all but that's not true in a general case and 
almost never true on mobile platforms. It is a viable solution but to 
make it work well the style should not use borders or bake in 
antialiasing (i.e. leave that to the client code).

I am concerned about something else - even with polygon generalization 
in place, the performance is not great. Zooming/panning is rather slow 
on my not so weak PC - the map would be unusable on a mobile device or 
at best it would be draining the battery quickly.

I've been looking into the code and I couldn't find anything related to 
polygon generalization. Where is it done? If it happens automatically in 
the Mapbox GL renderer that's too late - all the cost of preparing 
tiles, transmitting them, processing them in the client has already been 
incurred. Displaying data via WebGL is probably the cheapest part of the 
processing chain.


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