[OSM-dev] Migrating osm.org to vectors/Kartotherian

[Yuri Astrakhan]

Christoph, thanks for the explanation! Yes, sounds like each projection
would have to be generated and stored separatelly. Not that big of a deal
from Kartotherian perspective because it handles each tile source
independently, but it will require extra space and cpu. Also, it will
require osm2pgsql or other db update tool to generate multiple invalidation
tilesets in different projections.

On Sat, Oct 31, 2015 at 10:55 PM, Christoph Hormann <chris_hormann at gmx.de>
wrote:

> On Saturday 31 October 2015, Yuri Astrakhan wrote:
> >
> > Christoph, re multiple projections - if Mapnik implements vector tile
> > merging, we could in theory dynamicaly recombine tiles and change
> > projections, would't we? At a performance cost of course.
>
> First of all if you don't use the tiles as tiles but merge them into a
> full data set again there is no point in generating them in the first
> place of course.
>
> Apart from that regarding the abstract possibility: probably no for a
> number of reasons:
>
> - since mercator tiles don't include areas near the poles you will not
> be able to handle any projections that include the poles although
> better display of polar regions is of course one of the primary reasons
> for using other projections.
> - in general the tile edges in mercator will not be straight lines in
> other projections.  You would have to specifically take this into
> account when generating and processing the tiled data, otherwise you
> can't reproject the tiles without generating artefacts or invalid
> geometries.
> - you cannot map the zoom levels in one projection to those in another,
> especially not with the strongly variable scale of the mercator
> projection so unless your tiles are not zoom level specific you are
> screwed.
>
> These points apply to all generic geometry data in the tiles, any data
> specifically generated for rendering like label positions etc. is
> normally projection specific anyway.
>
> --
> Christoph Hormann
> http://www.imagico.de/
>
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