ransac_impl.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2020, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */
#pragma once

#include <mrpt/core/exceptions.h>
#include <mrpt/random/RandomGenerators.h>
#include <cstddef>
#include <vector>

// To be included from ransac.h only

namespace mrpt::math
{
template <typename NUMTYPE, typename DATASET, typename MODEL>
bool RANSAC_Template<NUMTYPE, DATASET, MODEL>::execute(
    const DATASET& data, const TRansacFitFunctor& fit_func,
    const TRansacDistanceFunctor& dist_func,
    const TRansacDegenerateFunctor& degen_func, const double distanceThreshold,
    const unsigned int minimumSizeSamplesToFit,
    std::vector<size_t>& out_best_inliers, MODEL& out_best_model,
    const double p, const size_t maxIter) const
{
    // Highly inspired on http://www.csse.uwa.edu.au/~pk/
    MRPT_START

    ASSERT_ABOVEEQ_(minimumSizeSamplesToFit, 1U);

    const size_t Npts = ransacDatasetSize(data);

    ASSERT_ABOVE_(Npts, 1);

    // Maximum number of attempts to select a non-degenerate data set.
    const size_t maxDataTrials = 100;

    // Sentinel value allowing detection of solution failure.
    out_best_model = MODEL();
    out_best_inliers.clear();

    size_t trialcount = 0;
    size_t bestscore = std::string::npos;  // npos will mean "none"
    size_t N = 1;  // Dummy initialisation for number of trials.

    std::vector<size_t> ind(minimumSizeSamplesToFit);

    while (N > trialcount)
    {
        // Select at random s datapoints to form a trial model, M.
        // In selecting these points we have to check that they are not in
        // a degenerate configuration.
        bool degenerate = true;
        size_t count = 1;
        std::vector<MODEL> MODELS;

        while (degenerate)
        {
            // Generate s random indicies in the range 1..npts
            ind.resize(minimumSizeSamplesToFit);

            // The +0.99... is due to the floor rounding afterwards when
            // converting from random double samples to size_t
            mrpt::random::getRandomGenerator().drawUniformVector(
                ind, 0.0, Npts - 1 + 0.999999);

            // Test that these points are not a degenerate configuration.
            degenerate = degen_func(data, ind);

            if (!degenerate)
            {
                // Fit model to this random selection of data points.
                // Note that M may represent a set of models that fit the data
                fit_func(data, ind, MODELS);

                // Depending on your problem it might be that the only way you
                // can determine whether a data set is degenerate or not is to
                // try to fit a model and see if it succeeds.  If it fails we
                // reset degenerate to true.
                degenerate = MODELS.empty();
            }

            // Safeguard against being stuck in this loop forever
            if (++count > maxDataTrials)
            {
                MRPT_LOG_WARN("Unable to select a nondegenerate data set");
                break;
            }
        }

        // Once we are out here we should have some kind of model...
        // Evaluate distances between points and model returning the indices
        // of elements in x that are inliers.  Additionally, if M is a cell
        // array of possible models 'distfn' will return the model that has
        // the most inliers.  After this call M will be a non-cell objec
        // representing only one model.
        unsigned int bestModelIdx = std::numeric_limits<unsigned int>::max();
        std::vector<size_t> inliers;
        if (!degenerate)
        {
            dist_func(
                data, MODELS, static_cast<NUMTYPE>(distanceThreshold),
                bestModelIdx, inliers);
            ASSERT_BELOW_(bestModelIdx, MODELS.size());
        }

        // Find the number of inliers to this model.
        const size_t ninliers = inliers.size();
        // Always update on the first iteration, regardless of the result (even
        // for ninliers=0)
        bool update_estim_num_iters = (trialcount == 0);

        if (ninliers > bestscore ||
            (bestscore == std::string::npos && ninliers != 0))
        {
            bestscore = ninliers;  // Record data for this model

            out_best_model = std::move(MODELS[bestModelIdx]);
            out_best_inliers = std::move(inliers);
            update_estim_num_iters = true;
        }

        if (update_estim_num_iters)
        {
            // Update estimate of N, the number of trials to ensure we pick,
            // with probability p, a data set with no outliers.
            double fracinliers = ninliers / static_cast<double>(Npts);
            double pNoOutliers =
                1 -
                pow(fracinliers, static_cast<double>(minimumSizeSamplesToFit));

            pNoOutliers = std::max(
                std::numeric_limits<double>::epsilon(),
                pNoOutliers);  // Avoid division by -Inf
            pNoOutliers = std::min(
                1.0 - std::numeric_limits<double>::epsilon(),
                pNoOutliers);  // Avoid division by 0.
            // Number of
            N = static_cast<size_t>(log(1 - p) / log(pNoOutliers));
            MRPT_LOG_DEBUG_FMT(
                "Iter #%u Estimated number of iters: %u  pNoOutliers = %f  "
                "#inliers: %u",
                (unsigned)trialcount, (unsigned)N, pNoOutliers,
                (unsigned)ninliers);
        }

        ++trialcount;

        MRPT_LOG_DEBUG_FMT(
            "trial %u out of %u", (unsigned int)trialcount,
            (unsigned int)ceil(static_cast<double>(N)));

        // Safeguard against being stuck in this loop forever
        if (trialcount > maxIter)
        {
            MRPT_LOG_WARN_FMT(
                "Warning: maximum number of trials (%u) reached\n",
                (unsigned)maxIter);
            break;
        }
    }

    if (!out_best_inliers.empty())
    {  // We got a solution
        MRPT_LOG_INFO_FMT("Finished in %u iterations.", (unsigned)trialcount);
        return true;
    }
    else
    {
        MRPT_LOG_WARN("Finished without any proper solution");
        return false;
    }

    MRPT_END
}

}  // namespace mrpt::math