2.2 SDO_RASTER Object Type and the Raster Data Table

In the GeoRaster object-relational model, a raster data table (RDT) is used to store all cell data in a raster image.

The cell data of a GeoRaster object is blocked, and each block is stored in the RDT as one row. You specify this table in the rasterDataTable attribute of the SDO_GEORASTER object, as explained in rasterDataTable Attribute. You must create the RDT before you store any cell data in it.

The RDT is an object table, defined as a table of SDO_RASTER object type or as a relational table that includes all columns defined by object type SDO_RASTER. The RDT name must be unique in the database, as described in Raster Data Table.

The SDO_RASTER object type is defined as:

CREATE TYPE sdo_raster AS OBJECT (
 rasterID           NUMBER,
 pyramidLevel       NUMBER,
 bandBlockNumber    NUMBER,
 rowBlockNumber     NUMBER,
 columnBlockNumber  NUMBER,
 blockMBR           SDO_GEOMETRY,
 rasterBlock        BLOB);

The sections that follow describe the semantics of each SDO_RASTER attribute.

• rasterID Attribute
  
• pyramidLevel Attribute
  
• bandBlockNumber Attribute
  
• rowBlockNumber Attribute
  
• columnBlockNumber Attribute
  
• blockMBR Attribute
  
• rasterBlock Attribute
  

2.2.1 rasterID Attribute

The rasterID attribute in the SDO_RASTER object must be a number that matches the rasterID value in its associated SDO_GEORASTER object. (The rasterID attribute of the SDO_GEORASTER object is described in rasterID Attribute.) The matching of these numbers identifies the raster block as belonging to a specific GeoRaster object.

2.2.2 pyramidLevel Attribute

The pyramidLevel attribute identifies the pyramid level for this block of cells. The pyramid level is 0 or any positive integer. Pyramid levels are used to create reduced resolution images that require less storage space. A pyramid level of 0 indicates the original raster data; that is, there is no reduction in the image resolution and no change in the storage space required. Values greater than 0 (zero) indicate increasingly reduced levels of image resolution and reduced storage space requirements. For more information about pyramids, see Pyramids.

This attribute and the bandBlockNumber attribute (described in bandBlockNumber Attribute) are also used to indicate bitmap masks and their pyramids. For more information about bitmap masks, bitmap mask pyramids, and how the pyramidLevel and bandBlockNumber attributes are used, see Bitmap Masks.

2.2.3 bandBlockNumber Attribute

The bandBlockNumber attribute identifies the block number along the band dimension. For information about bands and layers, see Bands_ Layers_ and Metadata. For more information about how the bandBlockNumber attribute is used with bitmap masks and their pyramids, see Bitmap Masks.

2.2.4 rowBlockNumber Attribute

The rowBlockNumber attribute identifies the block number along the row dimension.

2.2.5 columnBlockNumber Attribute

The columnBlockNumber attribute identifies the block number along the column dimension.

2.2.6 blockMBR Attribute

The blockMBR attribute is the geometry (of type SDO_GEOMETRY) for the minimum bounding rectangle (MBR) for this block. The geometry is in cell space (that is, its SRID value is null), and all ordinates are integers. The ordinates represent the minimum row and column and the maximum row and column stored in this block.

2.2.7 rasterBlock Attribute

The rasterBlock attribute contains all raster cell data for this block. It is also used to store bitmap masks of the GeoRaster object. The rasterBlock attribute is of type BLOB.