gvsend - extract several subsets from one GVAR dataset

gvsend - Extract several subsets from one GVAR dataset

SYNOPSIS

gvsend  [ parameter=value ]  [ inputfile ]

Parameters are: include_vars, output_files, range_pairs, all_inside, fix_missing, zero_bad, unit_affine.

DESCRIPTION

gvsend generates one or more subsets from a single input GVAR dataset. Subsets are specified in terms of earth transform coordinates, e.g., absolute visible channel coordinates.

gvsend can be run during live ingest. The input to gvsend can be the output from gvarin. gvsend reads the dim_counts variable to determine exactly how much data has been written for each GVAR channel. Network throughput determines how soon gvsend will finish after gvarin completes.

gvsend is most useful for distributing GVAR datasets across NFS (UNIX Network File System) in a timely fashion. It is not practical for gvarin to write output across NFS while ingesting live data; the input data rate is simply too high. Also, waiting for ingest to complete before transferring data is not ideal, because there is often no time break between GVAR images.

gvsend is very similar to gsubset, except that gsubset creates exactly one subset per input dataset, and that gsubset subsets do not have to instantiated. But, gsubset cannot instantiate a subset unless the input dataset is complete.

Unlike gsubset, gvsend can generate subsets when only part of the area specified in terms of earth transform coordinates is covered by all the input image variables. However, if the parameter all_inside=yes, gvsend requires the specified area to be entirely inside all the input image variables.

gvsend optionally fixes missing lines as they are encountered. The method used is similar to that used by gvarin. Only missing lines adjacent to good lines can be fixed. Consider the following example in which 'b' indicates missing data, and numbers indicate good data:

                 input                        output

            b b b b b b b b              b b b b b b b b
            b b b b b b b b              1 1 1 1 1 1 1 1
            1 1 1 1 1 1 1 1              1 1 1 1 1 1 1 1
            b b b b b b b b              1 2 1 2 1 2 1 2
            2 2 2 2 2 2 2 2              2 2 2 2 2 2 2 2
            b b b b b b b b              2 2 2 2 2 2 2 2
            b b b b b b b b              b b b b b b b b

gvsend can homogenize output subsets so they can be assembled with no earth location anomalies. If parameter unit_affine=yes, then the et_affine attribute in the output subsets is set to unity, and compensating changes are made to all image dimension scale and offsets. If unit_affine=no, then the ef_affine attribute is copied from each input dataset to corresponding output subset without change.

PARAMETERS

include_vars: List of variables to include in the output subsets. If the list is prefixed with a minus sign, the listed variables are excluded from the subsets. Wildcards * and ? are allowed. The default is to include all variables.

output_files: List of output files or directories. If a directory is specified, then the name of the corresponding output file will be directory/inputfile.

range_pairs: Minimum and maximum 1-relative limits for earth transform line (y) and sample (x), e.g.,

ymin ymax xmin xmax.

There must be four numbers for each output file. Limits are 1-relative. Minimums must not be greater than corresponding maximums. There is no default.

all_inside: If yes, the specified area must entirely covered by all input image variables, or no corresponding output is generated. If no, then an output dataset is generated if all input variables intersect the specified area. The default is yes.

fix_missing: If yes, all gaps of one or two missing lines are automatically fixed. If no, input data is copied to output datasets unaltered. The default is yes.

zero_bad: If yes, lines filled with zero's are assumed to be missing lines. If no, lines filled with the input variable's bad_value attribute are assumed to be missing lines. zero_bad should be yes when gvsend is running along with live ingest. The default is yes.

unit_affine: OPTIONAL. Controls whether or not the et_affine attribute in output subsets is going to be set to unity. Valid responses are [yes and no]. The default is yes.

EXAMPLES

The following range_pairs are good choices for GVAR image subsets:

 2985  6495 9260 17730 - Continental US
 2815 10110 8180 22010 - Extended Northern Hemisphere
 2595 13390 5900 24810 - Full Disk
 2815 7790  8180 22015 - Northern Hemisphere
10045 12480 8180 22010 - South Southern Hemisphere