Example: math_ransac_plane3d_example

This example shows how to use MRPT’s RANSAC C++ template to detect planes from a 3D point cloud given as a matrix (each row is a point).

See also the RANSAC tutorial page.

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2024, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */

#include <mrpt/gui/CDisplayWindow3D.h>
#include <mrpt/math/ransac.h>
#include <mrpt/opengl/CGridPlaneXY.h>
#include <mrpt/opengl/CPointCloud.h>
#include <mrpt/opengl/CTexturedPlane.h>
#include <mrpt/opengl/stock_objects.h>
#include <mrpt/poses/CPose3D.h>
#include <mrpt/random.h>
#include <mrpt/system/CTicTac.h>

#include <iostream>

using namespace mrpt;
using namespace mrpt::gui;
using namespace mrpt::math;
using namespace mrpt::random;
using namespace mrpt::poses;
using namespace mrpt::system;
using namespace std;

void ransac3Dplane_fit(
    const CMatrixDouble& allData,
    const std::vector<size_t>& useIndices,
    vector<CMatrixDouble>& fitModels)
{
  ASSERT_(useIndices.size() == 3);

  TPoint3D p1(allData(0, useIndices[0]), allData(1, useIndices[0]), allData(2, useIndices[0]));
  TPoint3D p2(allData(0, useIndices[1]), allData(1, useIndices[1]), allData(2, useIndices[1]));
  TPoint3D p3(allData(0, useIndices[2]), allData(1, useIndices[2]), allData(2, useIndices[2]));

  try
  {
    TPlane plane(p1, p2, p3);
    fitModels.resize(1);
    CMatrixDouble& M = fitModels[0];

    M.setSize(1, 4);
    for (size_t i = 0; i < 4; i++) M(0, i) = plane.coefs[i];
  }
  catch (exception&)
  {
    fitModels.clear();
    return;
  }
}

void ransac3Dplane_distance(
    const CMatrixDouble& allData,
    const vector<CMatrixDouble>& testModels,
    const double distanceThreshold,
    unsigned int& out_bestModelIndex,
    std::vector<size_t>& out_inlierIndices)
{
  ASSERT_(testModels.size() == 1);
  out_bestModelIndex = 0;
  const CMatrixDouble& M = testModels[0];

  ASSERT_(M.rows() == 1 && M.cols() == 4);

  TPlane plane;
  plane.coefs[0] = M(0, 0);
  plane.coefs[1] = M(0, 1);
  plane.coefs[2] = M(0, 2);
  plane.coefs[3] = M(0, 3);

  const size_t N = allData.cols();
  out_inlierIndices.clear();
  out_inlierIndices.reserve(100);
  for (size_t i = 0; i < N; i++)
  {
    const double d = plane.distance(TPoint3D(allData(0, i), allData(1, i), allData(2, i)));
    if (d < distanceThreshold) out_inlierIndices.push_back(i);
  }
}

bool ransac3Dplane_degenerate(const CMatrixDouble& allData, const std::vector<size_t>& useIndices)
{
  return false;
}

// ------------------------------------------------------
//              TestRANSAC
// ------------------------------------------------------
void TestRANSAC()
{
  getRandomGenerator().randomize();

  // Generate random points:
  // ------------------------------------
  const size_t N_plane = 300;
  const size_t N_noise = 100;

  const double PLANE_EQ[4] = {1, -1, 1, -2};

  CMatrixDouble data(3, N_plane + N_noise);
  for (size_t i = 0; i < N_plane; i++)
  {
    const double xx = getRandomGenerator().drawUniform(-3, 3);
    const double yy = getRandomGenerator().drawUniform(-3, 3);
    const double zz = -(PLANE_EQ[3] + PLANE_EQ[0] * xx + PLANE_EQ[1] * yy) / PLANE_EQ[2];
    data(0, i) = xx;
    data(1, i) = yy;
    data(2, i) = zz;
  }

  for (size_t i = 0; i < N_noise; i++)
  {
    data(0, i + N_plane) = getRandomGenerator().drawUniform(-4, 4);
    data(1, i + N_plane) = getRandomGenerator().drawUniform(-4, 4);
    data(2, i + N_plane) = getRandomGenerator().drawUniform(-4, 4);
  }

  // Run RANSAC
  // ------------------------------------
  CMatrixDouble best_model;
  std::vector<size_t> best_inliers;
  const double DIST_THRESHOLD = 0.05;

  CTicTac tictac;
  const size_t TIMES = 100;

  math::RANSAC myransac;
  for (size_t iters = 0; iters < TIMES; iters++)
  {
    myransac.setVerbosityLevel(iters == 0 ? mrpt::system::LVL_DEBUG : mrpt::system::LVL_INFO);

    myransac.execute(
        data, ransac3Dplane_fit, ransac3Dplane_distance, ransac3Dplane_degenerate, DIST_THRESHOLD,
        3,  // Minimum set of points
        best_inliers, best_model);
  }

  cout << "Computation time: " << tictac.Tac() * 1000.0 / TIMES << " ms" << endl;

  ASSERT_(best_model.rows() == 1 && best_model.cols() == 4);

  cout << "RANSAC finished: Best model: " << best_model << endl;
  //    cout << "Best inliers: " << best_inliers << endl;

  TPlane plane(best_model(0, 0), best_model(0, 1), best_model(0, 2), best_model(0, 3));

  // Show GUI
  // --------------------------
  mrpt::gui::CDisplayWindow3D win("Set of points", 500, 500);
  opengl::Scene::Ptr scene = opengl::Scene::Create();

  scene->insert(opengl::CGridPlaneXY::Create(-20, 20, -20, 20, 0, 1));
  scene->insert(opengl::stock_objects::CornerXYZ());

  opengl::CPointCloud::Ptr points = opengl::CPointCloud::Create();
  points->setColor(0, 0, 1);
  points->setPointSize(3);
  points->enableColorFromZ();

  {
    std::vector<double> xs, ys, zs;

    data.extractRow(0, xs);
    data.extractRow(1, ys);
    data.extractRow(2, zs);
    points->setAllPoints(xs, ys, zs);
  }

  scene->insert(points);

  opengl::CTexturedPlane::Ptr glPlane = opengl::CTexturedPlane::Create(-4, 4, -4, 4);

  glPlane->setColor_u8(mrpt::img::TColor(0xff, 0x00, 0x00, 0x80));  // RGBA

  TPose3D glPlanePose;
  plane.getAsPose3D(glPlanePose);
  glPlane->setPose(glPlanePose);

  scene->insert(glPlane);

  win.get3DSceneAndLock() = scene;
  win.unlockAccess3DScene();
  win.forceRepaint();

  win.waitForKey();
}

// ------------------------------------------------------
//                      MAIN
// ------------------------------------------------------
int main()
{
  try
  {
    TestRANSAC();
    return 0;
  }
  catch (const std::exception& e)
  {
    std::cerr << "MRPT error: " << mrpt::exception_to_str(e) << std::endl;
    return -1;
  }
}