Why am I seeing Two Kinds of HEADING2 Logs when Using two PP6Ds in Relative INS?

When working with relative INS, users can specify the ID of the master and rover via the DGPSTXIS and SETROVERID commands respectively. These IDs will then be output in the RELINSPVA and SYNCRELINSPVA logs. Also, please note that part of what gets set in relative INS is the ALIGN heading computation between the master and rover. Thus the output of HEADING2 at either master or rover is the ALIGN heading between the antenna at the master and the antenna at the rover.

Now, suppose we were doing relative INS between two ProPak6-D enclosures and logged HEADING2 ONNEW. In this case we are going to have an output that looks like the following:

#HEADING2A,FILE,0,14.5,FINESTEERING,1809,310398.400,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,-1.000000000,273.617034912,1.363533020,0.0,39.728641510,59.571094513,"DUAL",
"D31R",10,8,8,0,00,00,00,01*ec8c0606

#HEADING2A,FILE,0,14.5,FINESTEERING,1809,310398.400,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.777599275,23.183227539,57.660331726,0.0,122.950737000,80.250862122,"D31R",
"D55Y",13,7,7,0,00,00,00,01*675196e1

#HEADING2A,FILE,0,14.5,FINESTEERING,1809,310398.450,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.778322339,23.062273026,57.684009552,0.0,122.832885742,80.183685303,"D31R",
"D55Y",13,7,7,0,00,00,00,01*0157f3e8

#HEADING2A,FILE,0,14.5,FINESTEERING,1809,310398.500,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,-1.000000000,273.902252197,1.950430512,0.0,39.539623260,59.244056702,"DUAL",
"D31R",10,8,8,0,00,00,00,01*cb4302f1

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.600,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,-1.000000000,273.744934082,1.772883058,0.0,39.669944763,59.444198608,"DUAL",
"D31R",10,8,8,0,00,00,00,01*cdc7652b

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.500,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.776113510,23.406341553,57.784511566,0.0,123.765121460,80.295646667,"D31R",
"D55Y",13,7,7,0,00,00,00,01*96934c00

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.550,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.773651063,23.232831955,57.700504303,0.0,123.749855042,80.629035950,"D31R",
"D55Y",13,7,7,0,00,00,00,01*6a37be40

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.600,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.774977148,23.221822739,58.253822327,0.0,125.452735901,80.179885864,"D31R",
"D55Y",13,7,7,0,00,00,00,01*227f0e55

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.650,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.776588202,23.144947052,57.770359039,0.0,123.458915710,80.299728394,"D31R",
"D55Y",13,7,7,0,00,00,00,01*dbf276a0

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.700,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,-1.000000000,273.599090576,1.702725053,0.0,39.658290863,59.417480469,"DUAL",
"D31R",10,8,8,0,00,00,00,01*981ef061

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.700,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.773932934,23.677404404,57.565494537,0.0,123.554687500,80.599830627,"D31R",
"D55Y",13,7,7,0,00,00,00,01*3b9e1085

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.750,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,0.768025577,23.711599350,57.751277924,0.0,125.168289185,81.106864929,"D31R",
"D55Y",13,7,7,0,00,00,00,01*41fdb72b

#HEADING2A,FILE,0,17.5,FINESTEERING,1809,310398.800,00000000,1684,13020;SOL_COMPUTED,
NARROW_INT,-1.000000000,273.773223877,1.499056458,0.0,39.711566925,59.547901154,"DUAL",
"D31R",10,8,8,0,00,00,00,01*0863f85a

Please note the strings in bold in the HEADING2 logs above. These strings correspond to the RoverID field in the HEADING2 log. Some of the logs have this field set to "DUAL" whereas other logs have this field set to "D31R".  The "D31R" string corresponds to the RoverID that was set through the SETROVERID command mentioned earlier. These are the HEADING2 logs from the relative INS master to the relative INS rover.

The logs with the "DUAL" rover ID correspond to the heading logs from the ALIGN solution within the ProPa6D (i.e: using the OEM615 and OEM638 within the ProPak6-D) 

These heading logs with the "DUAL" Rover ID are used for:

  • INS alignment purposes
  • INS aiding to constrain heading drift

Depending on the ALIGN and Relative INS configurations, you can expect both sets of HEADING2 logs to show up at different rates.