LinearInterpolator.h

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/*
 * Copyright (C) 2012 by
 *   MetraLabs GmbH (MLAB), GERMANY
 * and
 *   Neuroinformatics and Cognitive Robotics Labs (NICR) at TU Ilmenau, GERMANY
 * All rights reserved.
 *
 * Contact: info@mira-project.org
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#ifndef _MIRA_LINEARINTERPOLATOR_H_
#define _MIRA_LINEARINTERPOLATOR_H_

#include <assert.h>

#include <limits>

#include <math/IsApprox.h>
#include <math/Lerp.h>
#include <math/IntervalFilter.h>

namespace mira {


class LinearInterpolator : public IntervalFilter
{
public:
    bool canExtrapolate() const { return true; }
    int samples() const         { return 2; }
    int samplesBefore() const   { return 1; }
    int samplesAfter() const    { return 1; }

    template <typename Tx, typename Ty, typename ContainerTx, typename ContainerTy>
    Ty apply(const ContainerTx& x, const ContainerTy& y, const Tx& xx)
    {
        assert(x.size()==y.size());
        assert(x.size()==2);

        double dx = (double)x.back() - (double)x.front();
        // check if dx is close to 0, then return the first
        if(isApprox(dx,0.0, std::numeric_limits<double>::epsilon()))
            return y.front();

        return lerp(y.front(), y.back(), ((double)xx-(double)x.front())/dx);
    }
};


class LinearInterpolatorNoExtrapolation : public IntervalFilter
{
public:
    bool canExtrapolate() const { return false; }
    int samples() const         { return 2; }
    int samplesBefore() const   { return 1; }
    int samplesAfter() const    { return 1; }

    template <typename Tx, typename Ty, typename ContainerTx, typename ContainerTy>
    Ty apply(const ContainerTx& x, const ContainerTy& y, const Tx& xx)
    {
        assert(x.size()==y.size());
        assert(x.size()==2);

        double dx = (double)x.back() - (double)x.front();
        // check if dx is close to 0, then return the first
        if(isApprox(dx,0.0, std::numeric_limits<double>::epsilon()))
            return y.front();

        return lerp(y.front(), y.back(), ((double)xx-(double)x.front())/dx);
    }
};


class LinearInterpolatorNearestNeighbourExtrapolator : public IntervalFilter
{
public:

    bool canExtrapolate() const { return true; }
    int samples() const         { return 2; }
    int samplesBefore() const   { return 1; }
    int samplesAfter() const    { return 1; }

    template <typename Tx, typename Ty, typename ContainerTx, typename ContainerTy>
    Ty apply(const ContainerTx& x, const ContainerTy& y, const Tx& xx)
    {
        assert(x.size()==y.size());
        assert(x.size()==2);

        // handle extrapolation case
        if (xx < x.front())
            return y.front();
        if (xx > x.back())
            return y.back();

        double dx = (double)x.back() - (double)x.front();
        // check if dx is close to 0, then return the first
        if(isApprox(dx,0.0, std::numeric_limits<double>::epsilon()))
            return y.front();

        return lerp(y.front(), y.back(), ((double)xx-(double)x.front())/dx);
    }
};


class LinearInterpolatorExtrapolationLimit : public IntervalFilter
{
public:
    LinearInterpolatorExtrapolationLimit(double limit = 1.0) :
        mLimit(limit) {}

    bool canExtrapolate() const { return true; }
    int samples() const         { return 2; }
    int samplesBefore() const   { return 1; }
    int samplesAfter() const    { return 1; }

    template <typename Tx, typename Ty, typename ContainerTx, typename ContainerTy>
    Ty apply(const ContainerTx& x, const ContainerTy& y, const Tx& xx)
    {
        assert(x.size()==y.size());
        assert(x.size()==2);

        double dx = (double)x.back() - (double)x.front();
        // check if dx is close to 0, then return the first
        if(isApprox(dx,0.0, std::numeric_limits<double>::epsilon()))
            return y.front();

        // check extrapolation case
        double alpha = ((double)xx-(double)x.front())/dx;
        if (alpha < -mLimit || alpha > (1 + mLimit))
            MIRA_THROW(XRuntime,
                       "LinearInterpolatorExtrapolationLimit: Lerp alpha " <<
                       "(" << alpha << ") out of specified limits " <<
                       "(" << -mLimit << ", " << 1 + mLimit << ")");

        return lerp(y.front(), y.back(), alpha);
    }

private:
    double mLimit;
};


} // namespace

#endif /* _MIRA_LINEARINTERPOLATOR_H_ */