PostGIS Raster : Extending PostgreSQL for The Support of ... - CoDE

elevation values at lidar points, only the ST_Value() function, that gives elevation values at particular
geometric points, is needed.
5.7.2 Intersect Rasters with Lines
In the case of geometric lines, this operation is used to extract elevation values for each road
segment in a road network.
SELECT roadID,
(ST_Intersection(geom, rast)).geom road,
(ST_Intersection(geom, rast)).val elevation
FROM roadNetwork, srtm
WHERE ST_Intersects(geom, rast)
User accesses the geometry and the value parts of the resulting set of geomval by surrounding
them with parentheses and adding .geom or .val at the end of the expression.
5.7.3 Intersect Rasters with Polygons
Figure 5.5: Intersection of raster and roads [23].
In the same way, user can extract temperature values for each polygon (circles in the following
example).
CREATE TABLE buff_temp AS
SELECT id, (gv).geom buffer, (gv).val temp
FROM (SELECT id, ST_Intersection(geom, rast) gv
FROM buffers, temperature
WHERE ST_Intersects(geom, rast))
Figure 5.6: Intersection of raster polygons [23].
Then, the result can also be used to compute the mean temperature for each polygon.
CREATE TABLE result AS
SELECT id,
sum(ST_Area(the_geom) * val) / sum(ST_Area(the_geom)) AS meantemp
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