Database Reference
In-Depth Information
ST_Transform() : This method converts the geometry's coordinates from
onespatialreferencesystemtoanother.Transformingageometryistypically
fasterthantransformingaraster.Transformingarasterrequiresresampling
thepixelvalues,acomputationally-intensive processandonethatcouldin-
troduceundesirableresults.Ifpossible,alwaystransformageometrybefore
transforming a raster.
ST_Intersects() :The ST_Intersects() methodfoundinthe JOIN ON
clause tests whether the raster tile and the geometry spatially intersect. It
willuseanyavailablespatialindexes.Dependingontheinstalledversionof
PostGIS, ST_Intersects() will implicitly convert the input geometry to a
raster (PostGIS 2.0) or the input raster to a geometry (PostGIS 2.1) before
comparing the two inputs.
ST_Clip() :Thismethodtrimseachintersectingrastertileonlytothearea
thatintersectsthegeometry.Iteliminatesthepixelsthatarenotspatiallypart
ofthegeometry.Aswith ST_Intersects() ,thegeometryisimplicitlycon-
verted to a raster before clipping.
ST_Union() : This method aggregates and merges the clipped raster tiles
into one raster for further processing.
The following output shows the average minimum temperature for San Francisco:
mean------------------7.35125005245209
SanFranciscowasreallycoldinJanuary,2012.So,howdoestherestof2012look?
Is San Francisco always cold?
SELECT
prism.month_year, (
ST_SummaryStats(
ST_Union(
ST_Clip(prism.rast, 2,
ST_Transform(sf.geom, 4322), TRUE)
),
1
)
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