[OSM-dev] OSM-Carto style, ported to vector tiles!

Christoph Hormann chris_hormann at gmx.de
Sun Jul 24 16:26:08 UTC 2016


On Sunday 24 July 2016, Rory McCann wrote:
>
> The problem (correct me if I'm wrong!) is that with vector tiles it's
> common to generate them only down to a certain zoom level (e.g. z14),
> and for lower zoom levels (z15+) to use the z14 tile, and just crop
> out the area you want, i.e. you are using the result of z14 SQL
> queries for z15+.
>
> The SQL queries are run when generating the .pbf vector tiles, and
> only go down to z14. For generating images, SQL isn't run and instead
> have to use the pregenerated pbf, and hence pregenerated way_pixels
> value. Hence you have to change the style, not the SQL.
>
> If you don't change it, areas that should appear at z15+ won't, since
> the way_pixels will be wrong for that zoom.

Ok - so you essentially say that use of !pixel_width! and !pixel_height! 
is - in the vector tiles system used - limited to the lower zoom 
levels.

That however would also mean you would need to remove all the 

way_area > 0.01*!pixel_width!::real*!pixel_height!::real

filters from SQL for z14 - otherwise you get missing geometries at the 
higher zooms (not a real lot - that limit is about one Mercator square 
meter at z14 - but when this occurs it would be visible and possibly 
surprising).

And if i understand you correctly this also means you cannot render any 
features differently on z14 and any higher zoom level based on 
processing done in SQL - unless you duplicate them into different 
separate layers for different zoom levels.

-- 
Christoph Hormann
http://www.imagico.de/



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