DynamicTimeWarp.cpp

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/* Author: Dave Coleman
 */
 
#include <ompl/tools/lightning/DynamicTimeWarp.h>
 
#include <utility>
 
namespace  // anonymous
{
    inline double min3(double n1, double n2, double n3)
    {
        return std::min(n1, std::min(n2, n3));
    }
}  // namespace
 
ompl::tools::DynamicTimeWarp::DynamicTimeWarp(base::SpaceInformationPtr si) : si_(std::move(si)), table_(1, 1)
{
    table_(0, 0) = 0.;
}
 
double ompl::tools::DynamicTimeWarp::calcDTWDistance(const og::PathGeometric &path1,
                                                     const og::PathGeometric &path2) const
{
    // Get lengths
    std::size_t n = path1.getStateCount();
    std::size_t m = path2.getStateCount();
    std::size_t nrows = table_.rows(), ncols = table_.cols();
 
    // Intialize table
    if (nrows <= n || ncols <= m)
    {
        table_.resize(n + 1, m + 1);
        for (std::size_t i = nrows; i <= n; ++i)
            table_(i, 0) = std::numeric_limits<double>::infinity();
        for (std::size_t i = ncols; i <= m; ++i)
            table_(0, i) = std::numeric_limits<double>::infinity();
    }
 
    // Do calculations
    double cost;
    for (std::size_t i = 1; i <= n; ++i)
        for (std::size_t j = 1; j <= m; ++j)
        {
            cost = si_->distance(path1.getState(i - 1), path2.getState(j - 1));
            table_(i, j) = cost + min3(table_(i - 1, j), table_(i, j - 1), table_(i - 1, j - 1));
        }
 
    return table_(n, m);
}
 
double ompl::tools::DynamicTimeWarp::getPathsScore(const og::PathGeometric &path1, const og::PathGeometric &path2) const
{
    // Copy the path but not the states
    og::PathGeometric newPath1 = path1;
    og::PathGeometric newPath2 = path2;
 
    // Interpolate both paths so that we have an even discretization of samples
    newPath1.interpolate();
    newPath2.interpolate();
 
    // compute the DTW between two vectors and divide by total path length of the longer path
    double max_states = std::max(newPath1.getStateCount(), newPath2.getStateCount());
 
    // Prevent division by zero
    if (max_states == 0)
        return std::numeric_limits<double>::max();  // the worse score possible
 
    return calcDTWDistance(newPath1, newPath2) / max_states;
}