CalcDOPs Application



The CalcDOPsManual tool reads SV almanac data (one file per day of observation) from a FIC, FICA, or a RINEX navigation file, then computes and displays visibility information. Dilution of precision values from that data are calculated using standard methods.

Command Summary

CalcDOPs [options]

Required Arguments:
Short Arg. Long Arg. Description
-i   Input file for day to be calculated.

Optional Arguments:
Short Arg. Long Arg. Description
-p   Input file for previous day (ephemeris mode only).
-o   Grid output file (default DOPs.out).
-sf   Stats output file (default DOPS.stat).
-tf   Time steps output file (default DOPS.times).
-l   Log output file (default DOPS.log).
-rs   Read from stats file.
-a   Work in almanac mode (ephemeris mode is default).
-w -s   Starting time tag.
-x   Exclude satellite PRN.
  Time spacing.
-na   North America only.
-d   Dump grid results at each time step (time-intensive).
-h --help Output options info and exit.
-v   Print version info and exit.

Abort/failure error codes given on return:

-1 Could not open data file.
-2 Could not identify input data file type.
-3 Fewer than 4 satellite almanacs available.
-4 Could not allocate GridStats data types.
-5 Could not open input stats file.
-6 Could not open output grid file.
-7 Could not open output stats file.
-8 Could not open output log file.

Essential variables not documented below at declaration:

NtrofN Number of cells/times with < 5 SVs visible during the time period.
NpeakH Number of cells/times w/ HDOP > 10.
NpeakP Number of cells/times w/ PDOP > 10.
IworstN Index in Grid of cells with worst nsvs (number of satellites).
IworstH Index in Grid of cells with worst HDOP.
IworstP Index in Grid of cells with worst PDOP.
WorstN Value of nsvs at IworstN.
WorstH Value of HDOP at IworstH.
WorstP Value of PDOP at IworstP.
TworstN Time tag (CommonTime) of WorstN.
TworstH Time tag (CommonTime) of WorstH.
TworstP Time Tag (CommonTime) of WorstP.


  1. GPS only, using PRNs hard-wired to SV numbers 1-32.
  2. Elevation limit is hard-wired to 5 degrees above horizon.
  3. "North America" means the northern half-hemisphere: -180 to 0 deg longitude, 0 to 90N latitude.
  4. Ephemeris mode is default, almanac mode is optional. Ephemeris mode is preferred, because it excludes unhealthy satellites for any time when they transmitted an unhealthy flag. Almanac mode will generally not exclude SVs when they were unhealthy (typical), or may erroneously exclude them for an entire day (rarely).
  5. If two input files are given, the default start time is midnight on the day to be calculated. A previous day input file can be given only in ephemeris mode, not almanac.
  6. The code uses geodetic coordinates for all calculations.
  7. The -d option is useful for e.g. making movies of DOPs throughout a day.

See also:

  • AIAA GPS Theory and Applications, vol. 1, Ed. Parkinson & Spilker, pp. 414.
  • GPS Signals, Measurements, and Performance, 2nd ed., Misra & Enge, pp. 203.

-- NicoleQuindara - 02 Aug 2011
Topic revision: r4 - 12 Jun 2015, UnknownUser

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