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40 lines
1.0 KiB
MySQL
40 lines
1.0 KiB
MySQL
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/******************************************************************************
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### TileBBox ###
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Given a Web Mercator tile ID as (z, x, y), returns a bounding-box
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geometry of the area covered by that tile.
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__Parameters:__
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- `integer` z - A tile zoom level.
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- `integer` x - A tile x-position.
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- `integer` y - A tile y-position.
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- `integer` srid - SRID of the desired target projection of the bounding
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box. Defaults to 3857 (Web Mercator).
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__Returns:__ `geometry(polygon)`
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******************************************************************************/
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create or replace function TileBBox(z int, x int, y int, srid int = 3857)
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returns geometry
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language plpgsql immutable as
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$func$
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declare
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max numeric := 20037508.34;
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res numeric := (max*2)/(2^z);
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bbox geometry;
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begin
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bbox := ST_MakeEnvelope(
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-max + (x * res),
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max - (y * res),
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-max + (x * res) + res,
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max - (y * res) - res,
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3857
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);
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if srid = 3857 then
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return bbox;
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else
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return ST_Transform(bbox, srid);
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end if;
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end;
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$func$;
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