4.1.3.3 TRIAD algorithm
The previous two algorithms treat gravity and magnetic
vector field as separate quantities. In TRIAD algorithm we
can use both gravity and magnetic vector simultaneously to
find the attitude represented by rotation matrix. This
problem of determining a rotation matrix needed to rotate
one reference vector (a vector reading in inertial / reference
frame) to another vector (a vector reading in body frame) is
first formulated by Wahba. Several solution has been
introduced to solve the Wahba Problem, most of them
recursive (i.e. QUEST algorithm). This recursive algorithm
to solve Wahba Problem offers the most accurate solution,
but from implementation consideration this recursive
algorithm will not guarantee the real time aspect needed for
the UAV autopilot control system. Fortunately there is one
non recursive solution for the Wahba Problem known as
TRIAD algorithm. Here is the formulation of the TRIAD
algorithm
The gravity vector and magnetic field vector can define a
Cartesian coordinate system, with unit vectors along three
axes i, j, and k. Two Cartesian systems can be determined
by two pairs of (ab, mb ) and (aR, mR)