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

Figure 4.39: Vector to raster conversion.
when working with analysis functions like ST_Intersection(). For instance, the intersection
operation can perform on vector and vector and results in a vector layer, or on vector and raster
with result as a vector/raster layer or on raster and raster with result as a raster layer.
Figure 4.40: Raster to vector conversion.
However, as each spatial object has a spatial reference identifier (SRID) and only spatial objects
with the same SRID can be used when performing spatial operations. So users have to ensure
that vectors or rasters should have the same SRID before executing some spatial operations on
them.
4.14 Data Formats
PostGIS Raster allows different forms to express raster data:
• Well Known TexT Well Known TexT (WKT) refers to the human readable text format. In the
context of PostGIS Raster, it is used when inserting and retrieving a raster from text format.
Example, the following request creates a raster from a line string with three bands (see Figure
4.41):
SELECT ST_AsRaster( ST_Buffer( ST_GeomFromText(’LINESTRING(50 50,150 150,150 50)’),
10), 200,200,ARRAY[’8BUI’, ’8BUI’, ’8BUI’], ARRAY[118,154,118], ARRAY[0,0,0])
Where ST_Buffer(geometry, radius) returns a new geometry that represents all points whose
distance from the geometry is less than or equal to radius.
Figure 4.41: Image formed by the raster [17].
48