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#include "survive_imu.h"
#include "linmath.h"
#include "math.h"
#include "survive_internal.h"
#include <memory.h>
#include <survive_imu.h>
// Mahoney is due to https://hal.archives-ouvertes.fr/hal-00488376/document
// See also http://www.olliw.eu/2013/imu-data-fusing/#chapter41 and
// http://x-io.co.uk/open-source-imu-and-ahrs-algorithms/
static void mahony_ahrs(SurviveIMUTracker *tracker, LinmathVec3d _gyro, LinmathVec3d _accel) {
LinmathVec3d gyro;
memcpy(gyro, _gyro, 3 * sizeof(FLT));
LinmathVec3d accel;
memcpy(accel, _accel, 3 * sizeof(FLT));
const FLT sample_f = tracker->so->imu_freq;
const FLT prop_gain = .5;
const FLT int_gain = 0;
FLT *q = tracker->pose.Rot;
FLT mag_accel = magnitude3d(accel);
if (mag_accel != 0.0) {
scale3d(accel, accel, 1. / mag_accel);
// Equiv of q^-1 * G
LinmathVec3d v = {q[1] * q[3] - q[0] * q[2], q[0] * q[1] + q[2] * q[3], q[0] * q[0] - 0.5 + q[3] * q[3]};
LinmathVec3d error;
cross3d(error, accel, v);
if (int_gain > 0.0f) {
LinmathVec3d fb_correction;
scale3d(fb_correction, error, int_gain * 2. / sample_f);
add3d(tracker->integralFB, tracker->integralFB, fb_correction);
add3d(gyro, gyro, tracker->integralFB);
}
scale3d(error, error, prop_gain * 2.);
add3d(gyro, gyro, error);
}
scale3d(gyro, gyro, 0.5 / sample_f);
LinmathQuat correction = {
(-q[1] * gyro[0] - q[2] * gyro[1] - q[3] * gyro[2]), (q[0] * gyro[0] + q[2] * gyro[2] - q[3] * gyro[1]),
(q[0] * gyro[1] - q[1] * gyro[2] + q[3] * gyro[0]), (q[0] * gyro[2] + q[1] * gyro[1] - q[2] * gyro[0])};
quatadd(q, q, correction);
quatnormalize(q, q);
}
static inline uint32_t tick_difference(uint32_t most_recent, uint32_t least_recent) {
uint32_t diff = 0;
if (most_recent > least_recent) {
diff = most_recent - least_recent;
} else {
diff = least_recent - most_recent;
}
if (diff > 0xFFFFFFFF / 2)
return 0x7FFFFFFF / 2 - diff;
return diff;
}
static const int imu_calibration_iterations = 100;
static void RotateAccel(LinmathVec3d rAcc, const SurvivePose *pose, const LinmathVec3d accel) {
quatrotatevector(rAcc, pose->Rot, accel);
LinmathVec3d G = {0, 0, -1};
add3d(rAcc, rAcc, G);
scale3d(rAcc, rAcc, 9.8066);
FLT m = magnitude3d(rAcc);
}
static void iterate_position(SurviveIMUTracker *tracker, double time_diff, const PoserDataIMU *pIMU, FLT *out) {
const SurvivePose *pose = &tracker->pose;
const FLT *vel = tracker->current_velocity;
for (int i = 0; i < 3; i++)
out[i] = pose->Pos[i];
FLT acc_mul = time_diff * time_diff / 2;
LinmathVec3d acc;
scale3d(acc, pIMU->accel, tracker->accel_scale_bias);
LinmathVec3d rAcc = {0};
RotateAccel(rAcc, pose, acc);
scale3d(rAcc, rAcc, acc_mul);
for (int i = 0; i < 3; i++) {
out[i] += time_diff * vel[i] + rAcc[i];
}
}
static void iterate_velocity(LinmathVec3d result, SurviveIMUTracker *tracker, double time_diff, PoserDataIMU *pIMU) {
const SurvivePose *pose = &tracker->pose;
const FLT *vel = tracker->current_velocity;
scale3d(result, vel, 1.);
LinmathVec3d acc;
scale3d(acc, pIMU->accel, tracker->accel_scale_bias);
LinmathVec3d rAcc = {0};
RotateAccel(rAcc, pose, acc);
scale3d(rAcc, rAcc, time_diff);
add3d(result, result, rAcc);
}
void survive_imu_tracker_integrate(SurviveObject *so, SurviveIMUTracker *tracker, PoserDataIMU *data) {
if (!tracker->is_initialized) {
tracker->pose.Rot[0] = 1.;
if (tracker->last_data.datamask == imu_calibration_iterations) {
tracker->last_data = *data;
const FLT up[3] = {0, 0, 1};
quatfrom2vectors(tracker->pose.Rot, tracker->updir, up);
tracker->accel_scale_bias = 1. / magnitude3d(tracker->updir);
tracker->is_initialized = true;
tracker->so = so;
return;
}
tracker->last_data.datamask++;
tracker->updir[0] += data->accel[0] / imu_calibration_iterations;
tracker->updir[1] += data->accel[1] / imu_calibration_iterations;
tracker->updir[2] += data->accel[2] / imu_calibration_iterations;
return;
}
for (int i = 0; i < 3; i++) {
tracker->updir[i] = data->accel[i] * .10 + tracker->updir[i] * .90;
}
mahony_ahrs(tracker, data->gyro, data->accel);
FLT time_diff = tick_difference(data->timecode, tracker->last_data.timecode) / (FLT)so->timebase_hz;
if (tick_difference(data->timecode, tracker->lastGTTime) < 3200000 * 3) {
FLT next[3];
iterate_position(tracker, time_diff, data, next);
LinmathVec3d v_next;
iterate_velocity(v_next, tracker, time_diff, data);
scale3d(tracker->current_velocity, v_next, 1);
scale3d(tracker->pose.Pos, next, 1);
}
FLT var_meters = .000001;
FLT var_quat = .05;
const FLT Q[7] = {var_meters, var_meters, var_meters, var_quat, var_quat, var_quat, var_quat};
// Note that this implementation is somewhat truncated. Instead of modeling velocity and velocities
// covariance with position explicitly, we just square the variance for the position indexes. This
// gives more or less the same calculation without having to do matrix multiplication.
for (int i = 0; i < 3; i++)
tracker->P[i] = tracker->P[i] * tracker->P[i] + Q[i];
for (int i = 3; i < 7; i++)
tracker->P[i] += Q[i];
tracker->last_data = *data;
}
void survive_imu_tracker_integrate_observation(SurviveObject *so, uint32_t timecode, SurviveIMUTracker *tracker,
SurvivePose *pose, const FLT *R) {
if (!tracker->is_initialized) {
tracker->pose = *pose;
return;
}
// Kalman filter assuming:
// F -> Identity
// H -> Identity
// Q / R / P -> Diagonal matrices; just treat them as such. This assumption might need some checking but it
// makes the # of calculations needed much smaller so we may be willing to tolerate some approximation here
FLT *xhat = &tracker->pose.Pos[0];
FLT *zk = &pose->Pos[0];
FLT yk[7];
for (int i = 0; i < 7; i++)
yk[i] = zk[i] - xhat[i];
FLT sk[7];
for (int i = 0; i < 7; i++)
sk[i] = R[i] + tracker->P[i];
FLT K[7];
for (int i = 0; i < 7; i++)
K[i] = tracker->P[i] / sk[i];
for (int i = 0; i < 7; i++)
xhat[i] += K[i] * yk[i];
for (int i = 0; i < 7; i++)
tracker->P[i] *= (1. - K[i]);
FLT time_diff = tick_difference(timecode, tracker->lastGTTime) / (FLT)so->timebase_hz;
for (int i = 0; i < 3; i++)
tracker->current_velocity[i] = 0.5 * (tracker->pose.Pos[i] - tracker->lastGT.Pos[i]) / time_diff;
tracker->lastGTTime = timecode;
tracker->lastGT = tracker->pose;
}
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