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Recommendations for using A.TOC files |
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Release 9.3
Last modified November 12, 2009 |
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A.TOC files are an image catalog in nature and construction; however, they are handled as a single raster dataset in ArcMap. Under this functional assumption, the A.TOC is expected to have one set of properties. For example, there can only be one cell size and one color map. But, A.TOC files are not always created to contain homogenous raster datasets.
There are two typical situations where A.TOC files are not supported by ArcGIS:
- The A.TOC file references data with different cell sizes. This occurs when parent directories of RPF data contain subfolders of data in different latitudinal zones. Each latitudinal zone has a different cell size.
- The A.TOC file references two kinds of an RPF product. If, for example, an A.TOC file references both GNC and JNC CADRG products, they will not work. According to their specifications, GNC and JNC CADRG products have different color maps to meet the needs of the intended use.
Due to the reasons mentioned above, it is generally recommended that A.TOC files are avoided in a production system. At first, they look like a worthwhile short cut, but in the end, they are problematic in ArcGIS. Referencing the RPF tiles directly is the most efficient way to use this raster data source in ArcGIS.
Additionally, when using ArcGIS Image Server, there is a performance advantage to referencing RPF tiles directly. When ArcGIS Image Server accesses data, it opens the file, reads the necessary pixels, performs the processing, and then closes the file. If it must open one large file, like an A.TOC, instead of a couple small files, like individual RPF tiles, there will be a performance hit.