GENERATION OF EARTH EXPLORER MISSION FILES

The Earth Explorer CFI software contains a set of functions that generate the following orbit files:

• Orbit Scenario files
• Predicted Orbit files
• Restituted Orbit files (DORIS restituted and DORIS precise)
• DORIS Navigator files
• Orbit Event files

The calling sequence to generate those files is quite simple (see next figure):

• Initialise the time correlations (create TimeCorrelation object) and the ModelId if required. This step is not needed for the generation of orbit event files.

• Call one of the static methods for the file generation from the class OrbitFunc

• Optionally for the generation of OSFs: it is possible to add orbital changes within the OSF by calling one of these methods:
  • OrbitFunc::genOsfAppendOrbitChange
  • OrbitFunc::genOsfRepeatCycle
  • OrbitFunc::genOsfAddDriftCycle

---

Example

Generation of an OSF and append one orbital change:

// ------------------------------------------------------------------------
//
//                           C++ Example Program.
//                           ORBIT FILES GENERATION
//
// ------------------------------------------------------------------------

// Non-EXPCFI include files
#include <string>
#include <vector>
#include <iostream>

// EXPCFI includes
#include "CfiError.h"
#include "TimeCorrelation.h"
#include "OrbitData.h"
#include "OrbitFunc.h"
#include "OrbitId.h"


// Namespaces
using namespace EECFI;
using namespace std;

// Main program
int main (int argc, char *argv[])
{ 

  //-------------------------------------------------
  // Put all the code inside try-catch statements
  //  so, if something fails, an exception is thrown
  //-------------------------------------------------
  try
  {  
    ModelId  modelId;
  
    // Initializing Time Reference: Used for the first and second example     
    double coorTime[4];

    coorTime[0]   = -1100.1000000000000;   // TAI time [days]
    coorTime[1]   = -1100.0995949074074;   // UTC time [days] (= TAI + 35.0 s)
    coorTime[2]   = -1100.0995914351852;   // UT1 time [days] (= TAI + 35.3 s)
    coorTime[3]   = -1100.099780092;       // GPS time [days] (= TAI + 19.0 s)
    
    TimeCorrelation timeCorr(coorTime);

    // ------------------------------------------------------------------------
    // Create OSF file.
    //-------------------------------------------------------------------------
    string outputDir = "./";
    string osfFile   = "OSF_FILE.xml";
    string fileClass = "EXAMPLE";
    string fhSystem  = "CFI_example";
    SatId  satId     = XOCFI_SAT_CRYOSAT;
    
    long   absOrbit      = 1;
    long   cycle         = 1;
    long   phase         = 1;
    long   versionNumber = 1;
    long   repeatCycle   = 369;
    long   cycleLength   = 5344;
    long   driftMode     = XOCFI_NOSUNSYNC_DRIFT;
    double mlstDrift     = -179.208556;
    double mlst          = 12.0;
    double anxLong       = 37.684960;

    double date          = 1643.395;
    
    double inclination;
    
    string outFile; // Name of the file created
    
    // With OrbitFunc class
    outFile = OrbitFunc::genOsf (satId,
                                 modelId,
                                 timeCorr,
                                 absOrbit,
                                 cycle,
                                 phase, 
                                 repeatCycle,
                                 cycleLength,
                                 anxLong,
                                 driftMode,
                                 inclination,
                                 mlstDrift,
                                 mlst, 
                                 date,
                                 outputDir,
                                 osfFile,
                                 fileClass,
                                 versionNumber,
                                 fhSystem);

    cout << endl << "File " << outFile << " created " << endl;

    // ------------------------------------------------------------------------
    // Append orbit change to OSF file.
    //-------------------------------------------------------------------------
    string outputFile     = "OSF_FILE_APPEND.xml";
    double oldNodalPeriod = 86400.0 * (1+mlstDrift/86400.0) *
                            (double)repeatCycle/(double)cycleLength;
    
    long   phaseInc       = XOCFI_NO_PHASE_INCREMENT;

    versionNumber++;
    absOrbit    = 5345;
    repeatCycle = 369;
    cycleLength = 5344;
    
    // small change wrt to nominal to check tolerances
    anxLong = 37.68497;
    mlst = mlst + mlstDrift*(5345-1)*oldNodalPeriod/(3600.0*86400.0) + 24.0;
    
    outFile = OrbitFunc::genOsfAppendOrbitChange( satId, 
                                                  modelId,
                                                  timeCorr,
                                                  osfFile,
                                                  absOrbit,
                                                  repeatCycle,
                                                  cycleLength,
                                                  anxLong, 
                                                  driftMode,
                                                  inclination,
                                                  mlstDrift, 
                                                  mlst,
                                                  phaseInc,
                                                  outputDir,
                                                  outputFile,
                                                  fileClass, 
                                                  versionNumber,
                                                  fhSystem );

    cout << endl << "File " << outFile << " created " << endl;
    
    // ------------------------------------------------------------------------
    // Change repeat cycle to OSF file.
    //-------------------------------------------------------------------------
    outputFile  = "OSF_FILE_CHANGE.xml";
    absOrbit    = 5000;
    phaseInc    = XOCFI_PHASE_INCREMENT;
    repeatCycle = 2;
    cycleLength = 29;
    anxLong     = 37.68497;
    driftMode   = XOCFI_NOSUNSYNC_INCLINATION;
    inclination = 92.0;

    versionNumber++;

    long searchDirection = XOCFI_SEARCH_FORWARD; 
    
    outFile = OrbitFunc::genOsfChangeRepeatCycle( satId, 
                                                  modelId, 
                                                  timeCorr, 
                                                  osfFile,
                                                  absOrbit, 
                                                  searchDirection,
                                                  repeatCycle,
                                                  cycleLength, 
                                                  anxLong, 
                                                  driftMode,
                                                  inclination,
                                                  mlstDrift,
                                                  phaseInc,
                                                  outputDir, 
                                                  outputFile,
                                                  fileClass, 
                                                  versionNumber,
                                                  fhSystem );
    cout << endl << "File " << outFile << " created " << endl;


  }//end try

  catch (CfiError cfiError)
  {
    //If an exception is thrown, there have been errors during execution
    vector<string> errorMessages;
    
    // Get error messages
    cfiError.getMsg(errorMessages);

    // Pring Error messages
    for (long i = 0; i < errorMessages.size(); i++)
    {
      cout << errorMessages[i] << endl;
    }
  }

  return 0;

}