Changes between Version 46 and Version 47 of WKTRaster/Documentation01

Timestamp:

Dec 10, 2009, 10:45:38 AM (14 years ago)

Author:

pracine

Comment:

—

WKTRaster/Documentation01

@@ -351 +351 @@
 '''The raster_columns Table'''
 
-Like the PostGIS "geometry_column" table, the PostGIS WKT Raster "raster_columns" table is a way for applications to get a quick overview of which tables have a raster column, and to get the main characteristics (metadata) of the rasters stored in these columns. Applications should maintain this table using the AddRasterColumn() and DropRasterColumn() functions, as there is no automatic mechanism in the database to keep this table up to date with every raster column created or deleted.
+Like the PostGIS "geometry_column" table, the PostGIS WKT Raster "raster_columns" table is a way for applications to get a quick overview of which tables have a raster column, and to get the main characteristics (metadata) of the rasters stored in these columns. Applications should maintain this table using the !AddRasterColumn() and !DropRasterColumn() functions, as there is no automatic mechanism in the database to keep this table up to date with every raster column created or deleted.
 
 Table 3 summarizes the attributes of the raster_columns table.
@@ -371 +371 @@
 || '''extent''' || geometry || Polygon geometry encompassing all raster rows of this table. NULL if predefined bounds are not known. When "regular_blocking" is set to true this polygon is a simple rectangle. In other cases it might be an irregular polygon. ||
 
+'''Storing in-db raster or registering out-db raster?'''
+
+One of the major PostGIS WKT Raster features is the ability to store raster data in the database or merely register them as external files residing in the filesystem. When registering a raster, only the raster metadata are stored in the database (width, height, number of band, georeference and path to the file), not the values associated with the pixels. Registering is done via the loader’s –R option. 
+
+ e.g. >gdal2wktraster –r c:/imagesets/landsat/image01.tif –t landsat -R
+
+'''Out-db raster''' is targeted at read-only applications. It has the following advantages:
+
+ * '''Access Speed -''' Speeds up the reading (and transmission) of web-ready rasters (JPEG, GIF, PNG) files for web applications as there is no need to convert them from the PostGIS raster type to a web friendly format.
+
+ * '''Seemless SQL Operators and Functions –''' All the operators and functions (except those involving write operations to the raster like ST_SetValue()) work seamlessly with out-db rasters.
+
+ * '''Simplified Backup –''' Rasters residing in the filesystem can be backed up once forever since they are not expected to be edited.
+
+ * '''Faster Database Loading –''' Initial table creation is faster since data do not have to be loaded/copied in the database.
+
+'''In-db raster''' is targeted at editing and analysis applications. It has the following advantages:
+
+ * '''Fast Analysis –''' Analysis operations involving pixel per pixel interpretation (ST_AsPolygon(), ST_Intersections(), etc…) are faster on in-db rasters since there is no need to read and extract the actual data from a JPEG or a TIFF format.
+
+ * '''Single storage solution –''' Provide a single vector/raster datasets storage solution. There is no need to backup the raster datasets separately from the vector datasets.
+
+ * '''Multi-Users Edition – T'''he database handles concurrent editing on raster only for in-db rasters.
 
 == '''3.2 - Integration with PostGIS''' ==