CRSplineInterpolator.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.
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 * Contact: info@mira-project.org
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#ifndef _MIRA_CRSPLINEINTERPOLATOR_H_
#define _MIRA_CRSPLINEINTERPOLATOR_H_

#include <math/IntervalFilter.h>

namespace mira {


class CRSplineInterpolator : public IntervalFilter
{
public:
    bool canExtrapolate() const { return true; }
    int samples() const         { return 4; }
    int samplesBefore() const   { return 2; }
    int samplesAfter() const    { return 2; }

    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()==4);

        const int k = 1; // this is fixed since we assume that we get exactly 4 values

        Ty mk   = (y[k+1]-y[k-1])/(x[k+1]-x[k-1]);
        Ty mkp1 = (y[k+2]-y[k])/(x[k+2]-x[k]);

        Tx scale = (x[k+1]-x[k]);

        Tx t = (xx-x[k])/scale;

        Tx t2 = t*t;
        Tx t3 = t2*t;

        // the hermite basis functions:
        Tx h00 = 2*t3-3*t2+1;
        Tx h10 = -h00+1;
        Tx h01 = t3-2*t2+t;
        Tx h11 = t3-t2;

        return h00*y[k] + h10*y[k+1] + h01*scale*mk + h11*scale*mkp1;
    }
};


} // namespace

#endif /* _MIRA_CRSPLINEINTERPOLATOR_H_ */