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Annex F

(Informative)

Raster Examples

F.1 Intermodule References

The figures below indicate the intermodule references of some global information and spatial object modules used in raster data transfers. These figures do not display all SDTS mandatory modules that must be transferred in accordance to SDTS.

Figure 29, Intermodule References with two or three Spatial Dimensions, displays a fairly typical raster data transfer. The External Spatial Reference module contains the external coordinate frame of reference for the entire transfer. The Raster Definition (RSDF) module has two records indicating that two raster objects are being transferred. The Internal Reference Foreign ID (IRID) links a IREF record and a RSDF record. Therefore each record of the RSDF module may have a different internal reference system, this allows each raster object to have a different resolution from the other raster objects. One raster object, described in the first record of the RSDF module, has three layers. The other raster object, described in the second record of the RSDF module has one layer. This is indicated by the foreign identifiers pointing to the four records of the Layer Definition (LDEF) module. There are two Cell modules containing all the cell values for each of the four raster layers. The LDEF module indicates which Cell module contains the cell values for that particular raster layer. The Cell modules could have one or more records (RCIDs) depending upon how the encoder chooses to format this module. There are three raster layers encoded in the Cell module named CEL1 and one layer in CEL2.

Figure 30 displays the intermodule references of a raster transfer having two or three geospatial dimensions and 5 non-geospatial dimensions. The XREF module contains the external coordinate frame of reference for the entire transfer. There can only be one XREF module in a transfer. The RSDF module has two records indicating that two raster objects are being transferred. Again, the Internal Reference Foreign ID field links the RSDF record to the IREF record. In addition the Dimension Definition (DMDF) records used by the Internal Reference record are linked by the Dimension Foreign ID fields (DMID). One raster object, described in the first record of the RSDF module, has three layers. The other raster object, described in the second record of the RSDF module has one layer. This is indicated by the foreign identifiers pointing to the four records of the LDEF module. The LDEF module indicates which Cell module contains the cell values for that particular raster layer. The Cell modules could have one or more records (RCIDs) depending upon how the encoder chooses to format this module.

F.2 SDTS Raster Objects

A raster object contains all raster data layers which have been collected and/or processed together, have similar geographic extents, and have the same resolution. A raster object is defined in one Raster Definition (RSDF) module record. Data layers within a raster object must share the same cell size (resolution). The cell size is defined in the Internal Spatial Reference (IREF) module record referenced by the ISID field of the RSDF module. One LDEF module record defines one layer of the raster object. A raster object could be composed of a single layer (Figure 31) or multiple layers (Figure 32). Both of these rasters have an Object Representation Code of G2, a 2-dimensional gridded raster.

Raster object A (Figure 31) has one data layer (or band). The geographic extent of raster object A is similar to raster object B (Figure 32). However, the data for each raster object was collected by different means. (example: scanned areal photography vs. satellite)

Raster object B has three data layers (or bands). For this example, all cell values of each data layer are interleaved in one Cell module. Thus, a Cell Sequence Code GJ, band interleaved by cell (pixel), would be indicated in the RSDF module when defining raster object B. Interleaving is not a requirement for raster objects with multiple layers.

These raster objects will be transferred in one SDTS transfer file set. Each raster object is defined in its own record of the Raster Definition (RSDF) module.

Raster Definition module record (RCID) 2 defines raster object A and contains the foreign identifier reference to the Layer Definition (LDEF) module record. The Layer Definition module record defines its one data layer. RCID 4 of the Layer Definition module also indicates the Cell module name where the cell values are found.

Raster Definition module RCID 1 defines raster object B and contains the foreign identifier references to the Layer Definition module records. There are three records in the Layer Definition module defining the three separate data layers. Each Layer Definition module record identifies the Cell module name where the cell values are found.

A separate Cell module could be created for each data layer of raster object B and thus, cell sequencing code GI would have been used. Having separate Cell modules for each raster layer is the most straight-forward type of SDTS - ISO 8211 encoding. The cell sequencing codes GI (band sequential), GJ (band interleaved by cell), and GL (band interleaved by pixel) determine whether raster layers are in separate Cell modules or interleaved within one Cell module.