Self-Calibration - Javad JNSGyro-4T Operator's Manual

S E T U P A N D M E A S U R I N G
JNSGyro-4T Setup

Self-Calibration

As follows from the definition of the attitude angles, the determination of
the body reference frame is the key issue. The body frame can be
determined using components of the vectors Master1 - Slave2, Master1 -
Slave3, and Master1 - Slave4 expanded in the body frame. Indeed, the body
frame is determined if the components of these vectors in the body frame
are known. Let us denote these vectors as X , X , X . To explicitly
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define the components of the vector X , the following setting is used:
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set,att/bl/0,{n12,r12,b12}
where n12, r12, and b12 are the nose, right, and belly components of the
vector X . Similarly, the components of the vectors X and X are
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specified by the settings
set,att/bl/0,{n13,r13,b13}
set,att/bl/0,{n14,r14,b14}
To measure the components of the above three vectors in the body frame,
the user must use measurement devices different from GNSS. If they are not
available, the following procedure, called self-calibration, is used. The self-
calibration makes the body frame determination easier.
Figure 3-5. Determination of the body frame by the self-calibration procedure
To perform the self-calibration procedure, the vehicle must be located on
the horizontal plane (which should be as close to the local horizon plane as
possible). Then, the axis Nose is defined as the projection of the vector X
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onto the local horizon plane. The axis Right lies in the local horizon plane,
is orthogonal to the axis Nose, and is directed to the right. The axis Belly
completes the right-oriented triple.
The attitude determination unit estimates the WGS-84 base line vectors,
averages a prescribed number of samples, and transforms the vectors to the
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