OdometryExample.py

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"""
GTSAM Copyright 2010-2018, Georgia Tech Research Corporation,
Atlanta, Georgia 30332-0415
All Rights Reserved
Authors: Frank Dellaert, et al. (see THANKS for the full author list)

See LICENSE for the license information

Simple robot motion example, with prior and two odometry measurements
Author: Frank Dellaert
"""
# pylint: disable=invalid-name, E1101

from __future__ import print_function

import numpy as np

import gtsam

import matplotlib.pyplot as plt
import gtsam.utils.plot as gtsam_plot

# Create noise models
ODOMETRY_NOISE = gtsam.noiseModel.Diagonal.Sigmas(np.array([0.2, 0.2, 0.1]))
PRIOR_NOISE = gtsam.noiseModel.Diagonal.Sigmas(np.array([0.3, 0.3, 0.1]))

# Create an empty nonlinear factor graph
graph = gtsam.NonlinearFactorGraph()

# Add a prior on the first pose, setting it to the origin
# A prior factor consists of a mean and a noise model (covariance matrix)
priorMean = gtsam.Pose2(0.0, 0.0, 0.0)  # prior at origin
graph.add(gtsam.PriorFactorPose2(1, priorMean, PRIOR_NOISE))

# Add odometry factors
odometry = gtsam.Pose2(2.0, 0.0, 0.0)
# For simplicity, we will use the same noise model for each odometry factor
# Create odometry (Between) factors between consecutive poses
graph.add(gtsam.BetweenFactorPose2(1, 2, odometry, ODOMETRY_NOISE))
graph.add(gtsam.BetweenFactorPose2(2, 3, odometry, ODOMETRY_NOISE))
print("\nFactor Graph:\n{}".format(graph))

# Create the data structure to hold the initialEstimate estimate to the solution
# For illustrative purposes, these have been deliberately set to incorrect values
initial = gtsam.Values()
initial.insert(1, gtsam.Pose2(0.5, 0.0, 0.2))
initial.insert(2, gtsam.Pose2(2.3, 0.1, -0.2))
initial.insert(3, gtsam.Pose2(4.1, 0.1, 0.1))
print("\nInitial Estimate:\n{}".format(initial))

# optimize using Levenberg-Marquardt optimization
params = gtsam.LevenbergMarquardtParams()
optimizer = gtsam.LevenbergMarquardtOptimizer(graph, initial, params)
result = optimizer.optimize()
print("\nFinal Result:\n{}".format(result))

# 5. Calculate and print marginal covariances for all variables
marginals = gtsam.Marginals(graph, result)
for i in range(1, 4):
    print("X{} covariance:\n{}\n".format(i, marginals.marginalCovariance(i)))

fig = plt.figure(0)
for i in range(1, 4):
    gtsam_plot.plot_pose2(0, result.atPose2(i), 0.5, marginals.marginalCovariance(i))
plt.axis('equal')
plt.show()