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4. LGA Processor Overview

4.1 LGAPROC Operation

4.1.1 Configuration Files

Before running LGAPROC, the operator must create a configuration file which describes the data to be processed. The configuration file contains several lines of data in the following format:

KEYWORD = VALUE

The valid keywords and expected values are listed in Table 1 below.

KeywordValueRequired
EPD_PKTFilename of EPD SFDU packets. Multiple EPD packet files may be listed. They will be read in the order they are listed.Y
AACS_PKTFilename of AACS SFDU packets.N
MAG_ASCFilename of ASCII MAG data.N
APPENDIf 'Y' then new data is appended to old files. If 'N' new files are created for all data. N
COORD_CENTERThe body to be the center of coordinates.  'Jupiter' is the normal value. N

4.1.2 Running LGAPROC

After creating the configuration file, LGAPROC can be executed. The executable will accept the name of the configuration file as a command line parameter. If no command line parameter is specified, the program will prompt the operator for the name of the configuration file.

No output is generated during the execution of LGAPROC. Successful completion of the program is indicated the return of the command prompt without error. The operator should inspect the log files mentioned below to determine if LGAPROC encountered any problems reading the data files.

4.1.3 Output

LGAPROC generates two files for each day of data processed. The first file is the archive file with record structure described in Section 3. The archive filenames are generated to match the year and day of the data contained in the files. For example, data collected during day 250 of 1996 would be stored in a file named 96250.lga. A log file is also generated corresponding to each archive file. In the above example, 96250.log would contain information about which packets LGAPROC processed. The log file will contain notation if EPD packets are out of sequence and if EPD packets cannot be matched with appropriate MAG and AACS data. No note will appear in the log file about missing MAG or AACS information if quick look files are being produced from EPD packets only.

4.2 LGAPROC Functions

The basic tasks performed by LGAPROC include the following:

  1. Initialize LGAPROC
    1. Acquire the name of the configuration file.
  2. Process LGA Packets
    1. Read SFCU packets and determine LGA packet type
    2. Discard any non-real time packets.
    3. Read in two real time packets. One contains count rate information, the other contains PHA and housekeeping data. Make sure that the two packets correspond to each other by checking sequence number and packet size.
    4. Extract time from LGA packet.
    5. Decompress the counts in the LGA packets and move them to the LGABLOCK data structure.
    6. Copy the subcom and PHA data to the LGABLOCK structure.
    7. Determine the amount of time spent in each sector.
      • based on number of science records per packet
      • correct for uneven coverage on start and stop motor positions
    8. Sum high resolution data into the lower resolution bins.
    9. Convert the counts in each bin to rates by dividing by times.
    10. Set the header information in the LGABLOCK structure
      • spacecraft position and orientation information
      • other header information
    11. Write the LGABLOCK record to the output file and repeat for the next set of LGA packets.

**Known deficiency of this document: "Still need to include a more complete description of the processing steps in the final version of LGAPROC; description of the sfdu.h and bits.h libraries." See other documents on this website.

Next: 5. LGAGEN Overview

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Updated 12/21/04, T. Hunt-Ward
tizby@ftecs.com