GVAR Descriptor Files

Descriptor File Naming Convention

The naming convention is: /data/descriptor, where descriptor is the descriptor file name. The default descriptor file names provided on SDI GVAR systems are:

ALL (list of all available GVAR images)
CONUS (Continental US)
NH (Northern Hemisphere)
SH (Southern Hemisphere)
FD (Full Disk)
OTHER (list of images that do not fall into any other category other than ALL)

Because of the variable scan characteristic of GVAR, a nearly infinite number of image sectors are possible, making rigidly defined descriptor file names impractical. Therefore, GVAR descriptor file names describe the minimum coverage an image must have to be listed in the respective file. Except for descriptor files ALL and OTHER, each GVAR descriptor file name listed above is defined locally in the /data/names.gvar file by listing the line and element of its four corners. When a new GVAR image becomes available (new index file), its four corners are compared to those of each GVAR descriptor listed above. If the new image completely contains the descriptor's boundary, it is listed in that file. All images are listed in at least two files. Some images are listed in several files. For example, an FD image is listed in the FD, NH, SH, CONUS and ALL files. No image is listed in the OTHER listing if it is listed in any file besides ALL.

As an example, the file /data/CONUS contains a list of all the GVAR index files on the SDI computer containing, at a minimum, an image of the continental US.

Descriptor File Format

Each GVAR descriptor file text entry has the following six fields

Field Name	Description
INDX_name	name of the index file describing this image
sline	starting image line number
eline	ending image line number
sele	starting image element number
eele	ending image element number
pos	absolute position number in the dataset - used by the ADDE Server

GVAR descriptors are defined in your site's /data/names.gvar configuration file. They indicate the image's area of coverage (e.g., CONUS for the continental US, or NH for the northern hemisphere) for a particular image. This file can be edited to help you find images for particular areas of interest using the Editing the names.gvar File procedure. However, remember that the images the SDI indicates for your specified area of interest contain entire images (at full resolution) for that time period. For example, if your area of interest is CONUS, the NH and FD (full disk) images also cover this area. However, much more data must be transferred for an FD image than for a CONUS image. Descriptor files are also used by the ADDE server.

The table below is an example of the /data/ALL descriptor file.

gvar.2006.063.160143.INDX 2973 9249 6512 17752 2
gvar.2006.063.160923.INDX 10037 9049 12496 22900 3
gvar.2006.063.161514.INDX 2805 9049 10120 22900 4
gvar.2006.063.163143.INDX 2973 9249 6512 17752 5
gvar.2006.063.163923.INDX 10037 9049 12496 22900 6
gvar.2006.063.164514.INDX 2805 9049 10120 22900 7

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