mirror of https://github.com/ArduPilot/ardupilot
91 lines
2.6 KiB
Matlab
91 lines
2.6 KiB
Matlab
function [...
|
|
nextQuat, ... % quaternion state vector after fusion of measurements
|
|
nextStates, ... % state vector after fusion of measurements
|
|
nextP, ... % state covariance matrix after fusion of corrections
|
|
innovation, ... % Declination innovation - rad
|
|
varInnov] ... %
|
|
= FuseMagnetometer( ...
|
|
quat, ... % predicted quaternion states
|
|
states, ... % predicted states
|
|
P, ... % predicted covariance
|
|
magData, ... % body frame magnetic flux measurements
|
|
measDec, ... % magnetic field declination - azimuth angle measured from true north (rad)
|
|
Tbn) % Estimated coordinate transformation matrix from body to NED frame
|
|
|
|
q0 = quat(1);
|
|
q1 = quat(2);
|
|
q2 = quat(3);
|
|
q3 = quat(4);
|
|
|
|
magX = magData(1);
|
|
magY = magData(2);
|
|
magZ = magData(3);
|
|
|
|
R_MAG = 0.1745^2;
|
|
|
|
H = calcH_MAG(magX,magY,magZ,q0,q1,q2,q3);
|
|
varInnov = (H*P*transpose(H) + R_MAG);
|
|
Kfusion = (P*transpose(H))/varInnov;
|
|
|
|
% Calculate the predicted magnetic declination
|
|
magMeasNED = Tbn*[magX;magY;magZ];
|
|
predDec = atan2(magMeasNED(2),magMeasNED(1));
|
|
|
|
% Calculate the measurement innovation
|
|
innovation = predDec - measDec;
|
|
|
|
if (innovation > pi)
|
|
innovation = innovation - 2*pi;
|
|
elseif (innovation < -pi)
|
|
innovation = innovation + 2*pi;
|
|
end
|
|
if (innovation > 0.5)
|
|
innovation = 0.5;
|
|
elseif (innovation < -0.5)
|
|
innovation = -0.5;
|
|
end
|
|
|
|
% correct the state vector
|
|
states(1:3) = 0;
|
|
states = states - Kfusion * innovation;
|
|
|
|
% the first 3 states represent the angular misalignment vector. This is
|
|
% is used to correct the estimate quaternion
|
|
% Convert the error rotation vector to its equivalent quaternion
|
|
% error = truth - estimate
|
|
rotationMag = sqrt(states(1)^2 + states(2)^2 + states(3)^2);
|
|
if rotationMag<1e-6
|
|
deltaQuat = single([1;0;0;0]);
|
|
else
|
|
deltaQuat = [cos(0.5*rotationMag); [states(1);states(2);states(3)]/rotationMag*sin(0.5*rotationMag)];
|
|
end
|
|
|
|
% Update the quaternion states by rotating from the previous attitude through
|
|
% the delta angle rotation quaternion
|
|
nextQuat = [quat(1)*deltaQuat(1)-transpose(quat(2:4))*deltaQuat(2:4); quat(1)*deltaQuat(2:4) + deltaQuat(1)*quat(2:4) + cross(quat(2:4),deltaQuat(2:4))];
|
|
|
|
% normalise the updated quaternion states
|
|
quatMag = sqrt(nextQuat(1)^2 + nextQuat(2)^2 + nextQuat(3)^2 + nextQuat(4)^2);
|
|
if (quatMag > 1e-6)
|
|
nextQuat = nextQuat / quatMag;
|
|
end
|
|
|
|
% correct the covariance P = P - K*H*P
|
|
P = P - Kfusion*H*P;
|
|
|
|
% Force symmetry on the covariance matrix to prevent ill-conditioning
|
|
% of the matrix which would cause the filter to blow-up
|
|
P = 0.5*(P + transpose(P));
|
|
|
|
% ensure diagonals are positive
|
|
for i=1:9
|
|
if P(i,i) < 0
|
|
P(i,i) = 0;
|
|
end
|
|
end
|
|
|
|
% Set default output for states and covariance
|
|
nextP = P;
|
|
nextStates = states;
|
|
|
|
end |