Geography Data Type - Divide Circle (Buffered Point) into 8 pieces like a pie

• keith.west-982594

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  May 1, 2012 at 9:56 am

  #260953

  I have a point that I am buffering by 1 mile to create a circle. I want to divide this circle (polygon) into 8 polygons each representing an equal portion of the circle like pieces of a pie.

  I then want to use those polygons to perform spatial queries.

  Here is what I have so far. If I could locate 8 points on the outer bounds of the circle, I could create a polyline from the centroid to each of the eight points and then do a difference on the two geography types. I cannot figure out how to locate the points on the bounding circle with each having a 45 degree angle.

  DECLARE @g geography;

  declare @h geography;

  SET @g = geography::STPointFromText('POINT(-122.34900 47.65100)', 4326);

  set @g = @g.STBuffer(1609)

  SELECT @g.ToString();

  select @g.STBuffer(1609).EnvelopeCenter() as Centroid, @g.STBuffer(1609) as BufferedPoint

  Any help is greatly appreciated.

  Keith

• keith.west-982594

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  Points: 965

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  May 9, 2012 at 11:57 am

  #1485232

  I figured this out. I created another polygon from lines that extend from the centroid outward in 8 directions for 3 degrees. I then create a multipolygon as a difference between my circle and the lines. Finally, I just created new polygons by indexing into the multipolygon.

  Here is my code.

  declare @g geography

  declare @line1 geography

  declare @line2 geography

  declare @line3 geography

  declare @line4 geography

  declare @line5 geography

  declare @line6 geography

  declare @line7 geography

  declare @line8 geography

  declare @poly1 geography

  declare @poly2 geography

  declare @poly3 geography

  declare @poly4 geography

  declare @poly5 geography

  declare @poly6 geography

  declare @poly7 geography

  declare @poly8 geography

  declare @Bandwidth float

  declare @Latitude float

  declare @Longitude float

  set @g = geography::Point(@Latitude, @Longitude, 4269)

  set @g = @g.STBuffer(@Bandwidth)

  set @line1 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude+0 AS VARCHAR(20)) + ' ' + CAST(@Latitude+3 AS VARCHAR(20))+')', 4269)

  set @line2 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude+3 AS VARCHAR(20)) + ' ' + CAST(@Latitude+3 AS VARCHAR(20))+')', 4269)

  set @line3 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude+3 AS VARCHAR(20)) + ' ' + CAST(@Latitude+0 AS VARCHAR(20))+')', 4269)

  set @line4 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude+3 AS VARCHAR(20)) + ' ' + CAST(@Latitude-3 AS VARCHAR(20))+')', 4269)

  set @line5 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude-0 AS VARCHAR(20)) + ' ' + CAST(@Latitude-3 AS VARCHAR(20))+')', 4269)

  set @line6 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude-3 AS VARCHAR(20)) + ' ' + CAST(@Latitude-3 AS VARCHAR(20))+')', 4269)

  set @line7 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude-3 AS VARCHAR(20)) + ' ' + CAST(@Latitude-0 AS VARCHAR(20))+')', 4269)

  set @line8 = geography::STLineFromText('LINESTRING(' + CAST(@Longitude AS VARCHAR(20)) + ' ' + CAST(@Latitude AS VARCHAR(20)) + ', ' + CAST(@Longitude-3 AS VARCHAR(20)) + ' ' + CAST(@Latitude+3 AS VARCHAR(20))+')', 4269)

  set @h = @line1.STUnion(@line2)

  set @h = @h.STUnion(@line3)

  set @h = @h.STUnion(@line4)

  set @h = @h.STUnion(@line5)

  set @h = @h.STUnion(@line6)

  set @h = @h.STUnion(@line7)

  set @h = @h.STUnion(@line8)

  set @multipoly = @g.STDifference(@h.STBuffer(.1))

  set @poly1 = @multipoly.STGeometryN(1)

  set @poly2 = @multipoly.STGeometryN(2)

  set @poly3 = @multipoly.STGeometryN(3)

  set @poly4 = @multipoly.STGeometryN(4)

  set @poly5 = @multipoly.STGeometryN(5)

  set @poly6 = @multipoly.STGeometryN(6)

  set @poly7 = @multipoly.STGeometryN(7)

  set @poly8 = @multipoly.STGeometryN(8)

  That created my 8 portion pie for my circle.

  Regards,

  Keith