120 lines
4.3 KiB
C++
120 lines
4.3 KiB
C++
/* ----------------------------------------------------------------------------
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* GTSAM Copyright 2010, Georgia Tech Research Corporation,
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* Atlanta, Georgia 30332-0415
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* All Rights Reserved
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* Authors: Frank Dellaert, et al. (see THANKS for the full author list)
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* See LICENSE for the license information
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* -------------------------------------------------------------------------- */
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/**
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* @file LIEKF_SE2_SimpleGPSExample.cpp
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* @brief A left invariant Extended Kalman Filter example using a Lie group
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* odometry as the prediction stage on SE(2) and
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*
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* This example uses the templated LIEKF class to estimate the state of
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* an object using odometry / GPS measurements The prediction stage of the LIEKF
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* uses a Lie Group element to propagate the stage in a discrete LIEKF. For most
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* cases, U = exp(u^ * dt) if u is a control vector that is constant over the
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* interval dt. However, if u is not constant over dt, other approaches are
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* needed to find the value of U. This approach simply takes a Lie group element
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* U, which can be found in various different ways.
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*
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* This data was compared to a left invariant EKF on SE(2) using identical
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* measurements and noise from the source of the InEKF plugin
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* https://inekf.readthedocs.io/en/latest/ Based on the paper "An Introduction
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* to the Invariant Extended Kalman Filter" by Easton R. Potokar, Randal W.
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* Beard, and Joshua G. Mangelson
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*
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* @date Apr 25, 2025
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* @author Scott Baker
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* @author Matt Kielo
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* @author Frank Dellaert
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*/
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#include <gtsam/geometry/Pose2.h>
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#include <gtsam/nonlinear/LIEKF.h>
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#include <iostream>
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using namespace std;
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using namespace gtsam;
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// Create a 2D GPS measurement function that returns the predicted measurement h
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// and Jacobian H. The predicted measurement h is the translation of the state
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// X.
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Vector2 h_gps(const Pose2& X, OptionalJacobian<2, 3> H = {}) {
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return X.translation(H);
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}
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// Define a LIEKF class that uses the Pose2 Lie group as the state and the
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// Vector2 measurement type.
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int main() {
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// // Initialize the filter's state, covariance, and time interval values.
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Pose2 X0(0.0, 0.0, 0.0);
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Matrix3 P0 = Matrix3::Identity() * 0.1;
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// Create the filter with the initial state, covariance, and measurement
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// function.
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LIEKF<Pose2> ekf(X0, P0);
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// Define the process covariance and measurement covariance matrices Q and R.
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Matrix3 Q = (Vector3(0.05, 0.05, 0.001)).asDiagonal();
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Matrix2 R = (Vector2(0.01, 0.01)).asDiagonal();
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// Define odometry movements.
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// U1: Move 1 unit in X, 1 unit in Y, 0.5 radians in theta.
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// U2: Move 1 unit in X, 1 unit in Y, 0 radians in theta.
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Pose2 U1(1.0, 1.0, 0.5), U2(1.0, 1.0, 0.0);
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// Create GPS measurements.
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// z1: Measure robot at (1, 0)
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// z2: Measure robot at (1, 1)
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Vector2 z1, z2;
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z1 << 1.0, 0.0;
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z2 << 1.0, 1.0;
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// Define a transformation matrix to convert the covariance into (theta, x, y)
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// form. The paper and data mentioned above uses a (theta, x, y) notation,
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// whereas GTSAM uses (x, y, theta). The transformation matrix is used to
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// directly compare results of the covariance matrix.
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Matrix3 TransformP;
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TransformP << 0, 0, 1, 1, 0, 0, 0, 1, 0;
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// Propagating/updating the filter
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// Initial state and covariance
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cout << "\nInitialization:\n";
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cout << "X0: " << ekf.state() << endl;
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cout << "P0: " << TransformP * ekf.covariance() * TransformP.transpose()
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<< endl;
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// First prediction stage
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ekf.predict(U1, Q);
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cout << "\nFirst Prediction:\n";
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cout << "X: " << ekf.state() << endl;
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cout << "P: " << TransformP * ekf.covariance() * TransformP.transpose()
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<< endl;
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// First update stage
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ekf.update(h_gps, z1, R);
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cout << "\nFirst Update:\n";
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cout << "X: " << ekf.state() << endl;
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cout << "P: " << TransformP * ekf.covariance() * TransformP.transpose()
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<< endl;
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// Second prediction stage
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ekf.predict(U2, Q);
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cout << "\nSecond Prediction:\n";
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cout << "X: " << ekf.state() << endl;
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cout << "P: " << TransformP * ekf.covariance() * TransformP.transpose()
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<< endl;
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// Second update stage
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ekf.update(h_gps, z2, R);
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cout << "\nSecond Update:\n";
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cout << "X: " << ekf.state() << endl;
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cout << "P: " << TransformP * ekf.covariance() * TransformP.transpose()
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<< endl;
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return 0;
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} |