By Soul Solutions on
Tuesday, 22 February 2011
I saw a question posed on twitter last week asking how to pass a SQL 2008 Geography as the bounding box to the many search engines on the web that now allow a spatial query. Flickr would be an example of this, the search api takes a bbox parameter described as:
A comma-delimited list of 4 values defining the Bounding Box of the area that will be searched. The 4 values represent the bottom-left corner of the box and the top-right corner, minimum_longitude, minimum_latitude, maximum_longitude, maximum_latitude. We had to do this for some SSRS maps we made and thanks to Rob Farley from LobsterPot we created this helper in SQL:
CREATE function [dbo].[GetLatLongBounds](@geo geography) returns table as return ( select MIN(@geo.STPointN(n.num).Lat) as MinLat, MAX(@geo.STPointN(n.num).Lat) as MaxLat, MIN(@geo.STPointN(n.num).Long) as MinLong, MAX(@geo.STPointN(n.num).Long) as MaxLong from dbo.nums n where n.num ) ; GO
This makes us of a table of numbers calls dbo.nums, a trick used widely when you need a list of all indexes:
CREATE TABLE [dbo].[nums]( [num] [int] NOT NULL, PRIMARY KEY CLUSTERED ( [num] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY]
Populate the table of numbers with the largest number you will need, we put a million numbers in there.
Use the bounds function like this, where you want the bounds returned for a particular GEO in MYTABLE with MYID of 42:
CROSS APPLY (SELECT * FROM [dbo].[GetLatLongBounds](g.GEO)) b
WHERE MYID = 42
The output is perfect for your next bounding box...
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