BLX is the format for storing topographic data in Magellan GPS units. This driver supports both reading and writing. In addition the 4 overview levels inherent in the BLX format can be used with the driver.
The BLX format is tile based, for the moment the tile size is fixed to 128x128 size. Furthermore the dimensions must be a multiple of the tile size.
The data type is fixed to Int16 and the value for undefined values is fixed to -32768. In the BLX format undefined values are only really supported on tile level. For undefined pixels in non-empty tiles see the FILLUNDEF/FILLUNDEFVAL options.
The BLX projection is fixed to WGS84 and georeferencing from BLX is supported in the form of one tiepoint and pixelsize.