From aa302c237dd1c9c5060a0f3a3fed7d08b69ea698 Mon Sep 17 00:00:00 2001
From: Paul Norman <penorman@mac.com>
Date: Mon, 8 Feb 2016 22:45:27 -0800
Subject: [PATCH] Use standard formula for CDB_ZoomFromScale

postgis-vt-util comes with a standard formula for zoom from
scaleDenominator, and this is well tested. This also fixes the
function throwing an error on NULL input.
---
 scripts-available/CDB_ZoomFromScale.sql | 40 +++++++------------------
 1 file changed, 11 insertions(+), 29 deletions(-)

diff --git a/scripts-available/CDB_ZoomFromScale.sql b/scripts-available/CDB_ZoomFromScale.sql
index 6ded82e..1c59041 100644
--- a/scripts-available/CDB_ZoomFromScale.sql
+++ b/scripts-available/CDB_ZoomFromScale.sql
@@ -1,30 +1,12 @@
-CREATE OR REPLACE FUNCTION cartodb.CDB_ZoomFromScale(scaleDenominator numeric) RETURNS int AS $$
-BEGIN
+CREATE OR REPLACE FUNCTION cartodb.CDB_ZoomFromScale(scaleDenominator numeric)
+RETURNS int
+LANGUAGE SQL
+IMMUTABLE
+AS $$
+SELECT
   CASE
-    WHEN scaleDenominator > 500000000 THEN RETURN 0;
-    WHEN scaleDenominator <= 500000000 AND scaleDenominator > 200000000 THEN RETURN 1;
-    WHEN scaleDenominator <= 200000000 AND scaleDenominator > 100000000 THEN RETURN 2;
-    WHEN scaleDenominator <= 100000000 AND scaleDenominator > 50000000 THEN RETURN 3;
-    WHEN scaleDenominator <= 50000000 AND scaleDenominator > 25000000 THEN RETURN 4;
-    WHEN scaleDenominator <= 25000000 AND scaleDenominator > 12500000 THEN RETURN 5;
-    WHEN scaleDenominator <= 12500000 AND scaleDenominator > 6500000 THEN RETURN 6;
-    WHEN scaleDenominator <= 6500000 AND scaleDenominator > 3000000 THEN RETURN 7;
-    WHEN scaleDenominator <= 3000000 AND scaleDenominator > 1500000 THEN RETURN 8;
-    WHEN scaleDenominator <= 1500000 AND scaleDenominator > 750000 THEN RETURN 9;
-    WHEN scaleDenominator <= 750000 AND scaleDenominator > 400000 THEN RETURN 10;
-    WHEN scaleDenominator <= 400000 AND scaleDenominator > 200000 THEN RETURN 11;
-    WHEN scaleDenominator <= 200000 AND scaleDenominator > 100000 THEN RETURN 12;
-    WHEN scaleDenominator <= 100000 AND scaleDenominator > 50000 THEN RETURN 13;
-    WHEN scaleDenominator <= 50000 AND scaleDenominator > 25000 THEN RETURN 14;
-    WHEN scaleDenominator <= 25000 AND scaleDenominator > 12500 THEN RETURN 15;
-    WHEN scaleDenominator <= 12500 AND scaleDenominator > 5000 THEN RETURN 16;
-    WHEN scaleDenominator <= 5000 AND scaleDenominator > 2500 THEN RETURN 17;
-    WHEN scaleDenominator <= 2500 AND scaleDenominator > 1500 THEN RETURN 18;
-    WHEN scaleDenominator <= 1500 AND scaleDenominator > 750 THEN RETURN 19;
-    WHEN scaleDenominator <= 750 AND scaleDenominator > 500 THEN RETURN 20;
-    WHEN scaleDenominator <= 500 AND scaleDenominator > 250 THEN RETURN 21;
-    WHEN scaleDenominator <= 250 AND scaleDenominator > 100 THEN RETURN 22;
-    WHEN scaleDenominator <= 100 THEN RETURN 23;
-  END CASE;
-END
-$$ LANGUAGE plpgsql IMMUTABLE;
+  -- Don't bother if the scale is larger than ~zoom level 0
+    WHEN scaleDenominator > 600000000 OR scaleDenominator = 0 THEN NULL
+    ELSE CAST (ROUND(LOG(2, 559082264.028/scaleDenominator)) AS INTEGER)
+  END;
+$$;