PlanarSLAMExample.py

Go to the documentation of this file.

"""
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 robotics example using odometry measurements and bearing-range (laser) measurements
Author: Alex Cunningham (C++), Kevin Deng & Frank Dellaert (Python)
"""
# pylint: disable=invalid-name, E1101

from __future__ import print_function

import gtsam
import numpy as np
from gtsam.symbol_shorthand import L, X

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


def main():
    """Main runner"""

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

    # Create the keys corresponding to unknown variables in the factor graph
    X1 = X(1)
    X2 = X(2)
    X3 = X(3)
    L1 = L(4)
    L2 = L(5)

    # Add a prior on pose X1 at the origin. A prior factor consists of a mean and a noise model
    graph.add(
        gtsam.PriorFactorPose2(X1, gtsam.Pose2(0.0, 0.0, 0.0), PRIOR_NOISE))

    # Add odometry factors between X1,X2 and X2,X3, respectively
    graph.add(
        gtsam.BetweenFactorPose2(X1, X2, gtsam.Pose2(2.0, 0.0, 0.0),
                                 ODOMETRY_NOISE))
    graph.add(
        gtsam.BetweenFactorPose2(X2, X3, gtsam.Pose2(2.0, 0.0, 0.0),
                                 ODOMETRY_NOISE))

    # Add Range-Bearing measurements to two different landmarks L1 and L2
    graph.add(
        gtsam.BearingRangeFactor2D(X1, L1, gtsam.Rot2.fromDegrees(45),
                                   np.sqrt(4.0 + 4.0), MEASUREMENT_NOISE))
    graph.add(
        gtsam.BearingRangeFactor2D(X2, L1, gtsam.Rot2.fromDegrees(90), 2.0,
                                   MEASUREMENT_NOISE))
    graph.add(
        gtsam.BearingRangeFactor2D(X3, L2, gtsam.Rot2.fromDegrees(90), 2.0,
                                   MEASUREMENT_NOISE))

    # Print graph
    print("Factor Graph:\n{}".format(graph))

    # Create (deliberately inaccurate) initial estimate
    initial_estimate = gtsam.Values()
    initial_estimate.insert(X1, gtsam.Pose2(-0.25, 0.20, 0.15))
    initial_estimate.insert(X2, gtsam.Pose2(2.30, 0.10, -0.20))
    initial_estimate.insert(X3, gtsam.Pose2(4.10, 0.10, 0.10))
    initial_estimate.insert(L1, gtsam.Point2(1.80, 2.10))
    initial_estimate.insert(L2, gtsam.Point2(4.10, 1.80))

    # Print
    print("Initial Estimate:\n{}".format(initial_estimate))

    # Optimize using Levenberg-Marquardt optimization. The optimizer
    # accepts an optional set of configuration parameters, controlling
    # things like convergence criteria, the type of linear system solver
    # to use, and the amount of information displayed during optimization.
    # Here we will use the default set of parameters.  See the
    # documentation for the full set of parameters.
    params = gtsam.LevenbergMarquardtParams()
    optimizer = gtsam.LevenbergMarquardtOptimizer(graph, initial_estimate,
                                                  params)
    result = optimizer.optimize()
    print("\nFinal Result:\n{}".format(result))

    # Calculate and print marginal covariances for all variables
    marginals = gtsam.Marginals(graph, result)
    for (key, s) in [(X1, "X1"), (X2, "X2"), (X3, "X3"), (L1, "L1"),
                     (L2, "L2")]:
        print("{} covariance:\n{}\n".format(s,
                                            marginals.marginalCovariance(key)))


if __name__ == "__main__":
    main()