Raster data

A PAMAP database can have zero or more raster (image) layers. In a PAMAP database, each layer covers the same area on the earth but each layer may be a different resolution. In order to comply with the GDB data model, the width of the database is reported as the width of the highest resolution layer. The height of the database is reported as the height of the highest resolution layer. When reading multiresolution databases, applications should access all layers as if they were of the highest resolution. GDB automatically replicates the pixel data for lower resolution layers.

PAMAP raster layers have either 1, 2, or 4 bytes per pixel. The mapping to GDB is as follows:

       PAMAP Size ->   GDB ->   PAMAP Size
       1               8U              1
       -               16S             2
       2               16U             2
       4               32R             4

Currently, PAMAP raster layers can only be written once. When a PAMAP database is created or a raster layer is added, the layer can be written and rewritten in any order. Once the file is closed though, existing layers can only be read.

PAMAP databases further distinguish a raster layer as being either a "Polygon Cover", "Reference Cover", or "Surface Cover", GDB can read all cover types. Only surface covers can be created and written to. The GDB model prohibits the creation of new raster layers other than at the highest resolution currently in the database.

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