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Positioning Application: Differences between default GPS constellation file satellite orbits and real GPS almanacs.

Environment/Versions
  • PosApp (SimGEN, SimREPLAYplus)
  • GPS

 

Answer
  • The table below shows the default GPS constellation parameters and which parameters are updated when you load a real Almanac file.
  • A blank cell indicates an Almanac parameter is not loaded in.
    • In this case the default constellation values are used.
  • The default GPS constellation parameters represent a perfect constellation.
    • This means your Scenario start time can be significantly different from the Reference time without any issues.
    • Real almanacs do not represent a perfect constellation so when loading in an almanac you should ensure your Scenario Start time is close to the Reference time.
      • If this is not the case then the orbits can diverge significantly and become unrealistic.
 
    Parameter loaded?
Parameter Default GPS Constellation YUMA RINEX SEM TLE
Reference time 5th Feb 2009 16:36:24 Y Y Y Y
Root Semi Major Axis 5153.700811 Y Y Y Y
Eccentricity 0 Y Y Y Y
Argument of Perigee default Y Y Y Y
Mean Anomaly default Y Y Y Y
Inclination 0.3055555555884 semicircles Y Y Y Y
Longitude of Ascending Node default Y Y Y Y
Mean Motion Difference 0   Y    
Inclination Rate 0   Y    
Right Ascension Rate 0 Y Y Y  
Clock Correction Af0 0 Y Y Y  
Clock Correction Af1 0 Y Y Y  
Clock Correction Af2 0   Y    
Nav Data Health All Healthy Y   Y  
Perturbations 0   Y    
Track Errors 0        
Group Delay 0   Y    
Satellite Signal Health All Healthy   Y Y  
Anti-Spoof (AS) Flag Disabled     Y  
SV Config Code Block II to IIR     Y  

 

 

Product : Positioning,SimREPLAYplus,SimGEN,PosApp,Almanac,GPS