3.4.2.3. POSMV Diagnostics¶

For accurate headings, we use the “heading accuracy” value to flag heading data as bad. A deviation of this value from baseline is usually associated with significant heading errors. The value of the “heading accuracy” field is not really “degrees”, but does indicate the degree of the problem.

Long, large excursions are very bad. Short excursions can be interpolated.

3.4.2.3.1. $PASHR message¶

Example: Good quality attitude:

The heading accuracy baseline is 0.012; we would throw out anything above 0.018. GAMS ==2 is good, alternating with 1 can be OK, solid 1 or 0 is bad. IMU should be 1.

Arrows indicates heading accuracy and GAMS

                                                        |   |
                                                        |   |
                                                        V   V
$PASHR,183944.821,74.52,T,-1.63,1.51,0.14,0.020,0.020,0.012,2,1*05
$PASHR,183945.321,74.41,T,-1.74,1.57,0.15,0.020,0.020,0.012,2,1*0C
$PASHR,183945.821,74.21,T,-1.76,1.56,0.17,0.020,0.020,0.012,2,1*00
$PASHR,183946.321,73.99,T,-1.67,1.52,0.19,0.020,0.020,0.012,2,1*06
$PASHR,183946.821,73.79,T,-1.46,1.45,0.22,0.020,0.020,0.012,2,1*0E
$PASHR,183947.321,73.65,T,-1.16,1.36,0.24,0.020,0.020,0.012,2,1*0E
$PASHR,183947.821,73.58,T,-0.78,1.26,0.24,0.020,0.020,0.012,2,1*03
$PASHR,183948.321,73.59,T,-0.38,1.16,0.22,0.020,0.020,0.012,2,1*07
       ^^^^^^^^^^ ^^^^^^^  ^^^^ ^^^^ ^^^^ ^^^^^ ^^^^^ ^^^^^ ^ ^\_/
          GGA     heading   ^     ^     ^   ^      ^    ^   ^ ^ ^
         decimal            |     |     |   |      |    |   | | |
          day               |     |     |   |      |    |   | | |
                            |     |     |   |      |    |   | | checksum
                            |     |     |   |      |    |   | |
                            |     |     |   |      |    |   | IMU flag
                            |     |     |   |      |    |   GAMS flag
                            |     |     |   |      |    |
                            |     |     |   |      |    heading accuracy
                            |     |     |   |   pitch accuracy
                            |     |     |  roll accuracy
                            |     |    heave
                            |     pitch
                          roll

GAMS flag: (0=no aiding, 1=GPS aiding, 2 = GAMS aiding)
IMU flag: (0 = no IMU; 1 = using IMU )

Example: Bad quality attitude:

This example has a heading accuracy of 1.303 (the actual error in the values could be much greater) and GAMS is 1.

$PASHR,143003.627,324.95,T,1.01,2.74,27.65,0.022,0.022,1.303,1,1*29
$PASHR,143004.627,324.69,T,2.40,1.98,27.59,0.022,0.022,1.303,1,1*25
$PASHR,143005.627,324.15,T,0.10,0.11,27.87,0.022,0.022,1.303,1,1*2B
       ^^^^^^^^^^ ^^^^^^^  ^^^^ ^^^^ ^^^^ ^^^^^ ^^^^^ ^^^^^ ^  ^\_/
                                                        ^   ^  ^ ^
                                                        |   |  | |
                                                        |   |  | |
                                                        |   |  | checksum
                                                        |   |  |
                                                        |   |  IMU flag
                                                        |   GAMS flag
                                                        |
                                                        heading accuracy

GAMS flag: (0=no aiding, 1=GPS aiding, 2 = GAMS aiding)
IMU flag: (0 = no IMU; 1 = using IMU )

On a UHDAS computer, you can query the logging system to see what the actual recent messages are by typing:

showlast.py -a20