ADU2 datasheet(85/162 Pages) ETC

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Command Response Formats

Page 73

The offset rotation angles (in degrees) align the 3DF attitude measurements given to

the desired vehicle coordinate system. These rotation angles must be determined by

some other accurate measurement device.

OFFSETS: heading(H), pitch(P), roll(R)

The offset rotation angles are normally 0.0. These numbers should not be changed

unless you have a case such as the following:

Occasionally mounting restrictions may require the antennas to be located from one

another such that the surveyed relative antenna position vectors (from file

BRFVEC.XYZ) do not directly provide the vehicle’s angular rotations (heading,

pitch, roll). In this situation, some other form of accurate measurement capability is

required to measure the offset angles (for example, a tape measure or a gyro-

theodolite).

For example, suppose that Antenna 1 and Antenna 2 could not be mounted exactly

along the heading direction of the vehicle and you chose the vector from Antenna 1 to

Antenna 2 to provide heading information. The installation software can determine a

1-2 relative antenna position vector, but the heading offset angle must be determined

with another precise measurement technique.

$PASHS,3DF,PKF,uuu,vvv,w.w,sx,y.y,sz

Sets the pitch Kalman filter parameters.

Three two-state Kalman filters are implemented in the ADU software to help predict

an approximate attitude of the vehicle at the current epoch. They are a heading and

heading rate filter, a pitch and pitch rate filter, and a roll and roll rate filter. Several

Kalman filter variables for heading, pitch, and roll are described below:

•

tau: Correlation time (sec) (default values are 999, 20, 20) - Any number

greater than 500 or 000 implies that the system model is an integration of a

random-walk process (or a constant velocity model).

•

To: Oscillation period (seconds) (default values are 0, 0, 0.) A zero implies

that no oscillation exists. For ship installations, an oscillation period exists

for both pitch and roll. This information aids the Kalman filter.

•

Q: Process noise power spectral density [(radian/sec2)2*sec] (Defaults are

1.0e-2, 4.0e-2, 4.0e-2). The default values are valid for low to medium

vehicle dynamics. High dynamics require higher values, such as 1.0.

•

R: Measurement noise scale factor (defaults are 1, 1, 1)

•

These variables may need tuning depending on the vehicle dynamics. When

set properly, the variables help the Kalman filter give a good estimate of

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