Create GetOpenLocationCode.sql

Author: victorvartan

GetOpenLocationCode.sql

@@ -0,0 +1,99 @@
+/****** Object:  StoredProcedure [dbo].[GetOpenLocationCode]    Script Date: 11/23/2018 4:18:59 PM ******/
+SET ANSI_NULLS ON
+GO
+SET QUOTED_IDENTIFIER ON
+GO
+-- =============================================
+-- Author: Victor-Vartan Pambuccian
+-- Create date: 2018-11-22
+-- Description: The MSSQL implementation of converting latitude and longitude to Open Location Code
+-- =============================================
+CREATE FUNCTION [dbo].[GetOpenLocationCode]
+(
+    @latitude DECIMAL(9,6), 
+    @longitude DECIMAL(9,6),
+    @codeLength INT = 10
+)
+RETURNS VARCHAR(MAX)
+AS
+BEGIN
+    DECLARE @code VARCHAR(MAX) = '';
+    DECLARE @CodePrecisionNormal INT = 10; -- Provides a normal precision code, approximately 14x14 meters.
+    DECLARE @CodePrecisionExtra INT = 11; -- Provides an extra precision code, approximately 2x3 meters.
+    DECLARE @Separator CHAR(1) = '+'; -- A separator used to break the code into two parts to aid memorability.
+    DECLARE @SeparatorPosition INT = 8; -- The number of characters to place before the separator.
+    DECLARE @PaddingCharacter CHAR(1) = '0'; -- The character used to pad codes.
+    DECLARE @CodeAlphabet CHAR(20) = '23456789CFGHJMPQRVWX'; -- The character set used to encode the values.
+    DECLARE @EncodingBase INT = LEN(@CodeAlphabet); -- The base to use to convert numbers to/from.
+    DECLARE @EncodingBaseSquared INT = @EncodingBase * @EncodingBase;
+    DECLARE @LatitudeMax INT = 90; -- The maximum value for latitude in degrees.
+    DECLARE @LongitudeMax INT = 180; -- The maximum value for longitude in degrees.
+    DECLARE @PairCodeLength INT = 10; -- Maxiumum code length using just lat/lng pair encoding.
+    DECLARE @GridColumns INT = 4; -- Number of columns in the grid refinement method.
+    DECLARE @GridRows INT = 5; -- Number of rows in the grid refinement method.
+
+    -- Check that the code length requested is valid.
+    IF (@codeLength < 4 OR (@codeLength < @PairCodeLength AND @codeLength % 2 = 1)) RETURN N'Illegal code length ' + CAST(@codeLength as NVARCHAR);
+
+    -- Ensure that latitude and longitude are valid.
+    SET @latitude = (SELECT MIN(x) FROM (VALUES ((SELECT MAX(x) FROM (VALUES (@latitude), (-@LatitudeMax)) AS value(x))), (@LatitudeMax)) AS value(x));
+    WHILE (@longitude < -@LongitudeMax) SET @longitude = @longitude + @LongitudeMax * 2;
+    WHILE (@longitude >= @LongitudeMax) SET @longitude = @longitude - @LongitudeMax * 2;
+	
+    -- Latitude 90 needs to be adjusted to be just less, so the returned code can also be decoded.
+    IF (@latitude = @LatitudeMax)
+    BEGIN
+        DECLARE @latitudePrecission DECIMAL(9,6);
+        IF (@codeLength <= @CodePrecisionNormal) SET @latitudePrecission = POWER(@EncodingBase, @codeLength / -2 + 2);
+        ELSE SET @latitudePrecission = POWER(@EncodingBase, -3) / POWER(@GridRows, @codeLength - @PairCodeLength);
+        SET @latitude = @latitude - 0.9 * @latitudePrecission;
+    END
+
+    -- Adjust latitude and longitude to be in positive number ranges.
+    DECLARE @remainingLatitude DECIMAL(9,6) = @latitude + @LatitudeMax;
+    DECLARE @remainingLongitude DECIMAL(9,6) = @longitude + @LongitudeMax;
+
+    -- Count how many digits have been created.
+    DECLARE @generatedDigits INT = 0;
+
+    -- The precisions are initially set to ENCODING_BASE^2 because they will be immediately divided.
+    DECLARE @latPrecision DECIMAL(9,6) = @EncodingBaseSquared;
+    DECLARE @lngPrecision DECIMAL(9,6) = @EncodingBaseSquared;
+
+    WHILE (@generatedDigits < @codeLength)
+    BEGIN
+        IF (@generatedDigits < @PairCodeLength)
+        BEGIN
+            -- Use the normal algorithm for the first set of digits.
+            SET @latPrecision = @latPrecision / @EncodingBase;
+            SET @lngPrecision = @lngPrecision / @EncodingBase;
+            DECLARE @latDigit INT = FLOOR(@remainingLatitude / @latPrecision);
+            DECLARE @lngDigit INT = FLOOR(@remainingLongitude / @lngPrecision);
+            SET @remainingLatitude = @remainingLatitude - @latPrecision * @latDigit;
+            SET @remainingLongitude = @remainingLongitude - @lngPrecision * @lngDigit;
+            SET @code = @code + SUBSTRING(@CodeAlphabet, @latDigit + 1, 1);
+            SET @code = @code + SUBSTRING(@CodeAlphabet, @lngDigit + 1, 1);
+            SET @generatedDigits = @generatedDigits + 2;
+        END
+        ELSE
+        BEGIN
+            -- Use the 4x5 grid for remaining digits.
+            SET @latPrecision = @latPrecision / @GridRows;
+            SET @lngPrecision = @lngPrecision / @GridColumns;
+            DECLARE @row INT = FLOOR(@remainingLatitude / @latPrecision);
+            DECLARE @col INT = FLOOR(@remainingLongitude / @lngPrecision);
+            SET @remainingLatitude = @remainingLatitude - @latPrecision * @row;
+            SET @remainingLongitude = @remainingLongitude - @lngPrecision * @col;
+            SET @code = @code + SUBSTRING(@CodeAlphabet, @row * @GridColumns + @col + 1, 1);
+            SET @generatedDigits = @generatedDigits + 1;
+        END;
+
+        -- If we are at the separator position, add the separator.
+        IF (@generatedDigits = @SeparatorPosition) SET @code = @code + @Separator;
+    END;
+
+    -- If the generated code is shorter than the separator position, pad the code and add the separator.
+    IF (@generatedDigits < @SeparatorPosition) SET @code = @code + REPLICATE(@PaddingCharacter, @SeparatorPosition - @generatedDigits) + @Separator;
+
+    RETURN @code;
+END;