Example: math_spline_interpolation

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2021, 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/CDisplayWindowPlots.h>
#include <mrpt/math/CSplineInterpolator1D.h>
#include <mrpt/math/utils.h>
#include <mrpt/poses/CPose3D.h>
#include <mrpt/poses/CPose3DInterpolator.h>
#include <mrpt/random.h>
#include <mrpt/system/datetime.h>
#include <mrpt/system/os.h>

#include <iostream>
#include <mrpt/math/interp_fit.hpp>

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

// ------------------------------------------------------
//              TestCapture
// ------------------------------------------------------
void TestCPose3DInterpolation()
{
    mrpt::Clock::time_point iniTs = mrpt::Clock::now();
    mrpt::Clock::time_point ts = iniTs;
    mrpt::Clock::time_point ots = iniTs;
    mrpt::poses::CPose3D pose(0, 0, 0, 0, 0, 0);
    mrpt::poses::CPose3DInterpolator poseInt;
    std::vector<mrpt::poses::CPose3D> p;
    mrpt::poses::CPose3D outPose(0, 0, 0, 0, 0, 0);
    bool valid;

    FILE* f = mrpt::system::os::fopen("interpolation.txt", "wt");

    // Set the maximum value of the interval time for considering interpolation
    poseInt.setMaxTimeInterpolation(std::chrono::seconds(1));

    poseInt.insert(ts, pose);  // First point

    ts += std::chrono::seconds(1);
    pose.setFromValues(1, 1, 0, 0, 1, 0);
    poseInt.insert(ts, pose);  // Second point

    ts += std::chrono::seconds(1);
    pose.setFromValues(2, 2.5, 1, 0, 1.3, 0);
    poseInt.insert(ts, pose);  // Third point

    ts += std::chrono::seconds(1);
    pose.setFromValues(3, 1.7, 2, 0, 1.57, 0);
    poseInt.insert(ts, pose);  // Fourth point

    unsigned int i;
    for (i = 0, ots = iniTs; ots <= iniTs + std::chrono::seconds(3);
         ots += std::chrono::milliseconds(100), i++)
    {
        poseInt.interpolate(ots, outPose, valid);
        p.push_back(outPose);
        mrpt::system::os::fprintf(
            f, "%d %f %f %f %f %f %f\n", i, outPose.x(), outPose.y(),
            outPose.z(), outPose.yaw(), outPose.pitch(), outPose.roll());
    }

    mrpt::system::os::fclose(f);

}  // end TestCPose3DInterpolation

void TestSplineInterpolation()
{
    FILE* f = mrpt::system::os::fopen("out2", "wt");

    CVectorDouble x, y;
    double t;
    x.resize(4);
    y.resize(4);

    // x[0] = 0.0;  x[1] = 1.0; x[2] = 2.0; x[3] = 4.0;
    // y[0] = 0.0;  y[1] = 1.0; y[2] = 1.8; y[3] = 1.6;

    x[0] = -1.5;
    x[1] = -0.5;
    x[2] = 0.5;
    x[3] = 1.5;
    y[0] = 3.14;
    y[1] = -3.10;
    y[2] = -3.05;
    y[3] = 3.10;

    CVectorDouble ts, ys_interp;

    for (t = x[1]; t <= x[2]; t += 0.01)
    {
        double w = mrpt::math::spline(t, x, y);  // wrap no
        //      double w = mrpt::math::spline(t, x, y, true); // wrap yes
        ts.push_back(t);
        ys_interp.push_back(w);
        mrpt::system::os::fprintf(f, "%f %f\n", t, w);
    }

    mrpt::system::os::fclose(f);
    cout << "Done" << endl;

#if MRPT_HAS_WXWIDGETS
    CDisplayWindowPlots figure("Interpolation results");
    figure.plot(x, y, "r.4", "true points");
    figure.plot(ts, ys_interp, "b", "interp");

    figure.axis_equal();
    figure.axis_fit();

    figure.waitForKey();
#endif
}

void TestSplineInterpolationVector()
{
    const size_t N = 15;
    CVectorDouble data_x, data_y(N);

    // Create random data:
    mrpt::math::linspace(-20.0, 20.0, N, data_x);
    getRandomGenerator().drawGaussian1DVector(data_y, 2.0, 1.0);

    // Create interpolator
    mrpt::math::CSplineInterpolator1D interp(data_x, data_y);

    // Generate sequence of where to interpolate:
    CVectorDouble xs;
    mrpt::math::linspace(-20.0, 20.0, 500, xs);

    CVectorDouble ys;
    bool valid = interp.queryVector(xs, ys);
    ASSERT_(valid);

#if MRPT_HAS_WXWIDGETS
    CDisplayWindowPlots figure("Interpolation results");
    figure.plot(data_x, data_y, "r.6", "true points");
    figure.plot(xs, ys, "b", "interp");

    figure.axis_equal();
    figure.axis_fit();

    figure.waitForKey();
#endif
}

int main(int argc, char** argv)
{
    try
    {
        TestSplineInterpolationVector();
        // TestSplineInterpolation();
        // TestCPose3DInterpolation();

        return 0;
    }
    catch (const std::exception& e)
    {
        std::cerr << "MRPT error: " << mrpt::exception_to_str(e) << std::endl;
        return -1;
    }
    catch (...)
    {
        printf("Another exception!!");
        return -1;
    }
}