An auxiliary (AUX or AUX.XML) file accompanies the raster in the same location and stores any auxiliary information that cannot be stored in the raster file itself.
An auxiliary file can store the following:
- Color map
- Statistics, histogram, or table
- Pointer to the pyramid file
- Coordinate system
- Projection information
Statistical information for the raster dataset is stored in the auxiliary file if it cannot be stored internally. It will be created automatically the first time statistics are required to perform a task on your raster layer. It might take longer to create this file for larger raster datasets, because more cells need to be accessed from which to derive the statistics. However, once the auxiliary file has been created, the statistics within it will be reused for future procedures that require statistical information.
The auxiliary file will also store a pointer to the pyramid file (either RRD or OVR) if pyramids have been created for your raster dataset. If you use the operating system to move the raster from its directory after pyramids have been built, the software will look in the location the pointer indicates to find the pyramid file. If it cannot find the pyramid file there, it will look in the directory into which you have moved the dataset. It is recommended that you copy or move datasets using ArcCatalog to make sure you copy all related files.
The auxiliary file will be created in the same directory as the source dataset if you have write access to the directory in which the dataset resides and the dataset itself. If you do not have write access to the directory in which the dataset resides and/or to the dataset itself, the auxiliary file will be written to the default proxy file.
ArcGIS 9.2 introduced the AUX.XML file for certain file formats. These AUX.XML files cannot be read by previous versions of ArcGIS.
The information stored in an AUX file is only accessible using a product from Esri, ERDAS, or a third-party product derived from the RDO/ERaster library.