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

Figure 4.48: Raster intersection paradigm [22].
Figure 4.49: Vector and raster intersection with a resulting raster layer [22].
sounds very useful because it helps PostGIS to vectorize only what is needed to do the requested
operation. As the intersection(vector,vector) → vector operation, the final result is a set of geometrypixel
value pairs representing the shared portion of the geometric and the vectorization of the raster
(see Figure 4.50).
Figure 4.50: Vector and raster intersection with a resulting vector layer [22].
Example 1.4: A raster and raster intersection with a raster layer as a result.
In the case of raster-raster intersection, the result is stored in a multiband raster. The extent of
the resulting raster corresponds to the geometrical intersection of the two raster extents. Nodata area
presenting in any band will result in nodata area in every band of the result. In other words, any pixel
intersecting with a nodata value pixel becomes a nodata value pixel in the result.
To obtain a result similar to the Intersection(vector/vector) → vector operation, the resulting
raster must be vectorized and moreover, this vectorization must take into account multiband.
Different possible scenarios will be one more time examined in the following part but in the case
of mutual exclusive polygons.
Example 2.1: A vector and vector intersection with a vector layer as a result. Here, in Figure 4.52,
the result is trivial.
Example 2.2: A vector and raster intersection with a raster layer as a result.
As in the previous case, the intersection operation results in different disjoint rasters, along with
additional attributes that come from input vectors (Figure 4.53). To obtain a result similar to the
intersection(vector,vector) → vector operation, the resulting rasters must be vectorized.
Example 2.3: A vector and raster intersection with a vector layer as a result.
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