A NODATA value is used for cells whose values are either not known or meaningless.

Each individual raster layer can have multiple NODATA values or NODATA value ranges, or both, associated with it. The GeoRaster metadata schema stores the NODATA information with each raster layer. Specifically, the NODATA values and value ranges associated with the object layer apply to any other sublayers. The NODATA values and value ranges for a sublayer is the union of those for the object layer and any NODATA metadata present in the sublayer. When you delete NODATA values or value ranges from a sublayer, any values or value ranges present in the object layer cannot be removed.

NODATA values and value ranges can be considered during resampling, for example, when pyramids are generated or when an image is generated by scaling. NODATA cells are by default treated as regular cells in those processes, to avoid dilations or erosions. However, when NODATA values or value ranges are chosen to be considered and the resampling method is BILINEAR, BIQUADRATIC, CUBIC, AVERAGE4, or AVERAGE16, then whenever a cell value involved in the resampling calculation is a NODATA value, the result of the resampling is also a NODATA value. The resulting NODATA value is the first NODATA value inside each resampling window, where the cell values are ordered row by row from the upper-left corner to the lower-right corner.

If you have GeoRaster objects from before release 11g with NODATA metadata stored in the raster description, that metadata is still valid for backward compatibility. The old NODATA value is considered to be object-wide, and it is moved to the object layer when you call the SDO_GEOR.addNODATA procedure on the object layer or when you call the SDO_GEOR.deleteNODATA procedure on the object layer without deleting the old NODATA value.

A NODATA value or value range is described using the SDO_RANGE_ARRAY type, which is defined as VARRAY(1048576) OF SDO_RANGE; the SDO_RANGE type specifies a lower and upper bound and is defined as (LB NUMBER, UB NUMBER).

• To specify a single number in an SDO_RANGE definition, specify LB as the number and UB as null. The following example specifies 2 as the NODATA value: SDO_RANGE_ARRAY(SDO_RANGE(2,NULL))

• SDO_RANGE(LB, UB) where LB=UB is considered the same as SDO_RANGE(LB, NULL).

• A real NODATA value range (where UB is not NULL and LB is less than UB) is inclusive at the lower bound and exclusive at the upper bound.

• You can specify multiple NODATA value ranges and individual NODATA values. The following example specifies one single NODATA value (5) and two NODATA value ranges (1,3) and (7,8): SDO_RANGE_ARRAY(SDO_RANGE(1,3), SDO_RANGE(5,NULL), SDO_RANGE(7,8))

Several PL/SQL subprograms perform operations (such as adding, removing, and querying) on NODATA values and value ranges associated with a GeoRaster layer.

In GeoRaster, a bitmap mask can be treated as a special type of NODATA, that is, a NODATA mask specifying one or more irregular areas as NODATA areas. In this case, the bitmap mask is not only identified in the bitmapMask element of the layerInfo metadata, but is also registered with the NODATA element of the layerInfo metadata. However, bitmap mask NODATA values are not considered during any resampling processing and statistical analysis.