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

Figure 3.5: Oracle GeoRaster georeference approach [14].
Figure 3.6: PostGIS Raster georeference approach [14].
referred to as storing out-database raster. With the second method, web or desktop applications may
access out-database rasters directly from the filesystem (such as JPEG files) and use most transparently
PostGIS Raster operators and functions on those rasters.
3.2.3 Indexing
The most important index is created on a GeoRaster object is a spatial index on the spatial extent
geometry of the GeoRaster object. Oracle GeoRaster creates spatial indexes over the footprint of raster
data while PostGIS Raster creates GiST indexes over the raster data itself. In Oracle GeoRaster,
spatial operations (like intersection) can only be done with the MBR of the data as the indexes are
created over the spatial extent. In PostGIS Raster, user can do really complex operations with raster
data like getting a set of geometry and geometry value from a given raster band (ST_DumAsPolygons()
function). Then, creating indexes over these raster data has more sense [15].
PostGIS Raster uses GDAL driver to calculate the georeferenced coordinates for upper and lower
corners (the spatial extent or footprint) of a raster. In this case, its spatial extent is the enclosing
geometry. Nervertheless, this is not necessarily in this way for Oracle GeoRaster.
In GeoRaster, one of the prerequisites for creating a spatial index over a geometry column is
that the USER_SDO_GEOM_METADATA view must contain an entry with the dimensions and coordinate
boundary information for the table column to be spatially indexed. So the following code will create
spatial index on the spatial extent geometry of the GeoRaster objects stored in table spain_images:
DELETE FROM user_sdo_geom_metadata
WHERE table_name = ’spain_images’
AND column_name = ’IMAGE.SPATIALEXTENT’;
INSERT INTO user_sdo_geom_metadata
VALUES (’spain_images’,’IMAGE.SPATIALEXTENT’,
SDO_DIM_ARRAY(SDO_DIM_ELEMENT(’X’, -180, 180, .00000005),
SDO_DIM_ELEMENT(’Y’, -90, 90, .00000005)), 4326);
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