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

Figure 4.31: In the right side: The mask. In the left side: the mask with the transparency set to 70%
overlays the digital elevation model raster [10].
4.13 Arrangements of Raster Layers
PostGIS Raster uses only one table for the raster data, the georeference and the metadata as
everything is stored in a single raster attribute. Thus raster attributes composing a raster table
are not related to each other to form a significant coverage. This choice makes the PostGIS Raster
structure very similar to the existing PostGIS vector structure. This also means that raster attributes
from the same table can be of different sizes, can snap to different grids and can overlap like polygons
in a vector layer can overlap.
Hence, how does a raster coverage (or a raster table) look like depends on the structure and the
relationships between the rasters that it contains. The following list represents different possible raster
table arrangements supported in PostGIS Raster:
1. A raster table may be referred to as an image warehouse of untiled and eventually unrelated
images. In this case, these images may or may not overlap since every image has its own
georeference. They may also have no georeference at all.
Figure 4.32: Image warehouse of untiled and unrelated images (4 images) [6].
This type of arrangement is intended for non-geographical users that employ raster data for web
sites or any other usage. That is because in this case, georeference information is not necessary
to be used. Furthermore, this soupless opens the door to other raster processing functions that
could be build from non-geographical users.
Figure 4.33: Image warehouse of cars [22].
2. A raster table may be an irregular tiled raster coverage. Its extent might not necessarily be
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