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Spatial queries in SQL Server 2008 SQL Bits III – 13 th September 2008
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New data types geometry and geography Spatial references Spatial operations Spatial indexes Case study
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80-90% of all data has a spatial element Where are your customers? Where are your assets? Where are potential customers? Where are the flood risks? Where are your complaints coming from? Where are the accident black-spots? Where are crimes happening?
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Postcodes in Glasgow Zoned Historical reasons G5 adjacent to G42 G40 in an island Postcodes designed for delivering letters
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The data analysis engine No useful rendering engine Virtual Earth Map Point Other GIS systems OGC Standards compliance Plus some “extension” methods of their own
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X/Y coordinate on a planar grid British National Grid Works well to ~750,000km 2 Different projections
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Geodetic coordinates Covers larger areas International datasets Approximation Earth actually flattened sphere (oblate spheroid) Different models Airy 1830 (used by OS) WGS84 (used by GPS)
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Spatial Reference Identifier All spatial data has an SRID SRIDs must match for spatial operations Null returned if SRIDs don’t match Geometry can have an SRID of 0 Not Geography.
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Point LineString Polygon GeomCollection MultiPolygon MultiLineString MultiPoint From BOL
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colin@scottishdevelopers.com http://www.colinmackay.net
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SELECT a.Name AS StartVenue, b.Name AS EndVenue, a.Location.STDistance(b.Location) / 1000.0 As Distance FROM Venue AS a INNER JOIN Venue AS b ON a.Id < b.Id ORDER BY a.Id, b.Id GCU60 Dundee U62102 MS TVP520537572 MS Edin’66658521 HBOSGCUDundee UMS TVP
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A linestring is a series of coordinates 1 dimension Defines a linear object Road Railway line River
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Can use STGeomFromText STGeomFromWKB STLineFromText STLineFromWKB Parse
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colin@scottishdevelopers.com http://www.colinmackay.net
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Geography uses SI Units Geometry uses the units of the planar system The square of the hypotenuse is equal to the sum of the square of the other two sides Not to scale 3 units 4 units ? units Distance from A to B: √(3 2 +4 2 ) = 5 A B
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colin@scottishdevelopers.com http://www.colinmackay.net
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A series of coordinates in a closed ring First and last coordinate are the same 2 dimensions Defines an area
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Interior is everything inside an anti-clockwise ring Everything on the left- hand side of the perimeter line.
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The specified input does not represent a valid geography instance because it exceeds a single hemisphere. Each geography instance must fit inside a single hemisphere. A common reason for this error is that a polygon has the wrong ring orientation.
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Can use STGeomFromText STGeomFromWKB STPolygonFromText STPolygonFromWKB Parse
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colin@scottishdevelopers.com http://www.colinmackay.net
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Estate Agent Filter by price, # bedrooms, type – EASY! Filter by location? Until now very vague
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N e a r a r a i l w a y s t a t i o n N e a r m y w o r k N e a r a m o t o r w a y j u n c t i o n Near a good school I n s i d e t h e c i t y O u t s i d e t h e c i t y
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Railway data Stations Routes
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colin@scottishdevelopers.com http://www.colinmackay.net
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Edinburgh - Glenrothes (via Kirkcaldy) Name DistKM -------------------------- ---------------- Edinburgh Waverley Station 0 Haymarket 1.89298770395887 South Gyle 6.95446540329848 Burntisland 12.086984317701 Dalmeny 12.49585147351 Kinghorn 13.1439998546632 Aberdour 13.3392361220632 North Queensferry 14.3833962761344 Dalgety Bay 15.0082794626365 Inverkeithing 15.7316327831032 Kirkcaldy 17.9484646860063 Glenrothes With Thornton 23.7022936117453
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colin@scottishdevelopers.com http://www.colinmackay.net
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Decomposes space into 4 levels of grid Level 1 is the top Cells are uniform in a level A level can be a 4x4, 8x8 or 16x16 grid 8x8 by default
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Table must have a primary key Primary key cannot subsequently be changed. Not on views Maximum of 249 Spatial indexes per column
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Where geometry/ geography sizes vary e.g. Rail routes Small: Suburban lines Large: Intercity lines
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Supports STIntersects STEquals STDistance One Geography must be a point Both sides of the spatial operation must have the same SRID
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Must specify boundary of spatial area Additional methods supported STContains STOverlaps STTouches STWithin
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CodePlex project More spatial methods Aggregations Scripts http://www.codeplex.com/sqlspatialtools
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GML Import and export M and Z Can store Cannot operate. Other spatial Operations Geometry has more! Visualisation .NET application integration Data Importing
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Slide Deck on my website http://www.colinmackay.net http://www.colinmackay.net Blog posts on Spatial Data http://blog.colinmackay.net http://blog.colinmackay.net
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