compSatVis/compStaVis Applications



This pair of programs compute station visibility to a constellation of space vehicles (SVs) and SV visiblity to a set of stations. The output is a set of tables that provide statistics such as the average number of stations visible to a SV, minimum and maximum number of SVs visible to a station over a specified period, and amount of time a station has more than a specified number of SVs visible.

The programs are driven by command-line arguments, a file containing station positions, and a file of SV orbital information in any of several formats.

Command Summary

compSatVis [options]
compStaVis [options]

where [options] can be

-h, --help Display argument list
-p, --int Interval in seconds
-n, --nav Name of navigation file(s).
-t, --type Navigation file type: must be (one of)
  YUMA - Yuma format
  SEM - SEM format
  SP3 - SP3 format
  RNAV - RINEX navigation file
  FALM - FIC almanac format
  FEPH - FIC ephemeris format
-o, --output Name of output file
-c, --mscfile Monitor station coordinates file. Monitor Station Coordinates File Format contains information on how to specify station location
-e, --minelv Minimum elevation angle (degrees)
-i, --include Include this station in the calculations. One or more -i options may be given. If at least one -i option is given all stations not designated with the -i option will be excluded from the calculations.
-x, --exclude Exclude this station in the calculations. By default, all stations in the monitor station coordinates file are sued in the calculations. This option specifies the a station is to be excluded. Multiple -x options are allowed in order to exclude multiple stations.
-s, --start-time Start time for evaluation period (m/d/y H:M)
-z, --end-time End time for evaluation period (m/d/y H:M)
-m, --max-SV Maximum number of SVs tracked simultaneously (compStaVis only). Default = 12.
-m, --min-SV Minimum number of stations visible to an SV simultaneously (compSatVis only). Default = 2.
-D, --detail Print SV or station results for each interval. This section of the output file is in form of a comma separated values (CSV) suitable for input to Excel. If only one (1) station is being evaluated, the list of SVs present at each interval will be listed.
-H, --Healthy Consider only healthy SVs (requires FIC ephemeris or Rinex nav file). When the -D option is used AND only one station is being evaluated, -H also control the level of detail in the list of SV PRN IDs. -H once will cause SVs with non-zero health in subframe 1 to be omitted from the list of PRNs. -H -H (two time) will cause SVs to remain in the list, but each unhealthy SVs will marked with the suffix HLTH.

Usage examples

Example 1. Generating satellite visibility statistics using the SEM almanac from the USCG Navigation Center.

user@host:~$ compSatVis -ovisout.txt -ncurrent.al3 -tSEM -cstations.msc -e10 -p60 -s"01/16/2008 00:00"
This example loads SEM almanac data from the file current.al3 and a list of station locations from the file stations.msc. It then calculates the number of satellites visible to each station found at each 60 sec interval from 0000Z to 2356Z of Jan 13, 2008. using a 10 degree minimum elevation angle. The results are written to the file visout.txt. Note the use of a specific start time. The SEM and Yuma almanac formats contain an almanac reference week, which is generally in the range 0-1023 (the existing format definitions are ambiguous and SEM and Yuma almanacs with full week numbers have been reported, at least anecdotally). If the -s command is not specified, compSatVis/compStaVis will use whatever reference time is given in the almanac file, which may result in unexpected results. Example results for a specific set of IGS stations are given here.

Example 2. Generating station visibility statistics using the SEM almanac from the USCG Navigation Center.

user@host:~$ compStaVis -ovisout.txt -ncurrent.al3 -tSEM -cstations.msc -e10 -p60 -s"01/16/2008 00:00"
Same as Example 1, however, the values calculated and the statistics will reflect the number of stations visible to each satellite. Example results for a specific set of IGS stations are given here.

Example 3. Generating satellite visibility statistics using the Yuma almanac from the USCG Navigation Center.

user@host:~$ compSatVis -ovisout.txt -ncurrent.alm -tYUMA -cstations.msc -e10 -p60 -s"01/13/2008 00:00" -z"01/16/2008 23:59"
Similar to Example 1, but the statistics are computed over four complete days.

Example 4. Generating satellite visibility statistics using SP3 files.

user@host:~$ compSatVis -ovisout.txt -napc14622 -napc14623 -napc14624 -tSP3 -cstations.msc -e10 -p60
Similar to Example 1, however, navigation message data are from three SP3 files. It is necessary to load three SP3 files to cover the default sidereal day period because the methods that calculate SV positions from the SP 3 data use interpolation and need data from the previous day and the following day in order to have sufficient points for the interpolation. In this example in which no evaluation period is specified, compSatVis derives coverage for the "middle day" for the period.

Platforms Supported

This application has been successfully used in Linux. This application successfully builds under these environments: linux-x86, linux-x86_64, others tbd.

Assumptions and Defaults

An ellipsoidal Earth corresponding to the WGS-84 geoid is assumed. Horizon obstructions are not taken into account.

If the time span of the evaluation is not set via the -s and -z commands, the programs default to determining the epoch time of the navigation message data and computing statistics from 0000Z - 2356Z of the corresponding day. This is default is derived from the GPS orbit characteristics which cause the ground tracks to repeat every day minus four minutes. As a result, for a given set of GPS orbital information, the statistics should be nearly identical for successive 23h 56m periods. The -s and -z arguments were added for two reasons, (1.) to support future GNSS constellation that do not have the repeating ground track feature of GPS, (2.) the -s also enables potential ambiguity in the almanac reference week to be resolved (for Yuma and SEM almanac data formats).

The program assumes receivers can track all SVs in view. However, the -m (max-SV) option has been added to help address the limitation of this assumption. The -m option tells compStaVis to report the number of intervals for which the number of SVs in view exceed the specified value. Assuming all receivers in the network under consideration can track the same number of SVs, the -s option provides a way in which the user can obtain information on the amount of time the receiver will be "saturated", i.e. have all tracking channels in use.

The -m option in compSatVis is useful in checking various station networks against desired minimum coverage. compSatVis counts the number of intervals in which the number of stations visible to an SV is less than the number specified in the -m option (default of 2).

Whenever the -i or -x options are invoked, the output file will contain a list of the specific stations used in the analysis. Otherwise, the output file simply notes that all stations in the monitor station coordinates file were used.

See also:

Topic revision: r14 - 05 Aug 2011, NicoleQuindara

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