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Limit the maximum zoom level

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Avoid returning zoom levels greater than the maximum
'safe' level. For a zero denominator (which would imply
and infinite zoom level) return the maximum level too.
This commit is contained in:
Javier Goizueta 2016-05-27 12:19:47 +02:00
parent aa302c237d
commit 0b3ad5e569
1 changed files with 17 additions and 2 deletions
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17
scripts-available/CDB_ZoomFromScale.sql
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@ -1,3 +1,17 @@
-- Maximum supported zoom level
CREATE OR REPLACE FUNCTION _CDB_MaxSupportedZoom()
RETURNS int
LANGUAGE SQL
IMMUTABLE
AS $$
-- The maximum zoom level has to be limited for various reasons,
-- e.g. zoom levels greater than 31 would require tile coordinates
-- that would not fit in an INTEGER (which is signed, 32 bits long).
-- We'll choose 20 as a limit which is safe also when the JavaScript shift
-- operator (<<) is used for computing powers of two.
SELECT 29;
$$;
CREATE OR REPLACE FUNCTION cartodb.CDB_ZoomFromScale(scaleDenominator numeric)
RETURNS int
LANGUAGE SQL
@ -7,6 +21,7 @@ SELECT
CASE
-- Don't bother if the scale is larger than ~zoom level 0
WHEN scaleDenominator > 600000000 OR scaleDenominator = 0 THEN NULL
ELSE CAST (ROUND(LOG(2, 559082264.028/scaleDenominator)) AS INTEGER)
WHEN scaleDenominator = 0 THEN _CDB_MaxSupportedZoom()
ELSE CAST (LEAST(ROUND(LOG(2, 559082264.028/scaleDenominator)), _CDB_MaxSupportedZoom()) AS INTEGER)
END;
$$;