![](https://csdnimg.cn/release/download_crawler_static/10540330/bgb.jpg)
NCOM Manual
Revision: 150615
11
Table 5. Navigation status (byte 21) definitions
Value Struct. Description
0 A All quantities in the packet are invalid.
1 A Raw IMU measurements. These are output at roughly 10 Hz before the system is
initialised. They are useful for checking the communication link and verifying the
operation of the accelerometers and angular rate sensors in the laboratory. In this
mode only the accelerations and angular rates are valid, they are not calibrated or to
any specification. The information in the other fields is invalid.
2 A Initialising. When GPS time becomes available the system starts the initialisation
process. The strapdown navigator and Kalman filter are allocated, but do not yet
run. Angular rates and accelerations during this time are output 1 s in arrears. There
will be a 1 s pause at the start of initialisation where no output will be made (while
the system fills the buffers). The system has to run 1 s in arrears at this time in
order to synchronise the GNSS data with the inertial data and perform the
initialisation checks.
During the initialising mode the time, acceleration and angular rate fields will be
valid. Approximate (very inaccurate) position, velocity and angles may be output.
3 A Locking. The system will move to locking mode when the conditions for
initialising are correct. To initialise, GPS time, position and velocity must be
available; roll and pitch must be estimated (assumed approximately zero with the
“vehicle level” option); heading must be estimated from forward velocity, dual
antenna static initialisation or user command.
In locking mode the system runs in arrears but catches up by 0.1 s every 1 s;
locking mode lasts 10 s. During locking mode the outputs are not real-time, but all
fields are valid.
4 A Locked. In Locked mode the system is outputting real-time data with the specified
latency guaranteed. All fields are valid.
5 A Reserved for “unlocked” navigation output. Do not use any values from this
message.
6 A Expired firmware: this is output if the firmware is time limited and the expiry time
has passed.
7 A Blocked firmware: this is output if the firmware has been blocked (by password
protection).
10 A Status only. Only the Batch S part of the message (Bytes 63–70) should be
decoded. This is used at the start of some logged NCOM files in order to save a
complete set of status messages before the real data begins.
11 B Internal Use. Do not use any values from this message.
20 A Trigger packet while “initialising” (see Navigation status 2 for more details). The
Status channel (byte 62) will have a value of 24 (falling trigger), 43 (rising trigger),
65 (output trigger), 79 (falling trigger 2), 80 (rising trigger 2) or 81 (output trigger
2), depending on what triggers the packet.
This packet is generated following a short variable delay (less than 0.02 s) after the
corresponding navigation data output. The Time output is that of the trigger event.
21 A Trigger packet while “locking” (see Navigation status 3 for more details). The
Status channel (byte 62) will have a value of 24 (falling trigger), 43 (rising trigger),
65 (output trigger), 79 (falling trigger 2), 80 (rising trigger 2) or 81 (output trigger