interpol1d.h

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#pragma once

/*
________________________________________________________________________

 (C) dGB Beheer B.V.; (LICENSE) http://opendtect.org/OpendTect_license.txt
 Author:        Bert & Kris
 Date:          Mar 2006
________________________________________________________________________

*/

#include "undefval.h"

/*\brief Interpolation for regular and irregular sampling.

  You have to supply the values 'just around' the position.
  In regular sampling, the sample values are spaced in an equidistant manner.

  When you have undefs, there may be a utility which behaves as follows:
  * When the nearest sample value is undefined, return undefined
  * When another value is undef, use a value from a sample near that sample
    and continue the interpolation.

  The position where the interpolation is done is needed.
  A 'float x' must be provided which will be 0 <= x <= 1 in almost all
  cases.

  When things become a bit difficult, the parameters for the interpolation can
  be calculated up front. Then, you'll find a class with an 'apply' method.
  The position for apply is usually between v0 and v1, but doesn't
  _need_ to be. In that case, 0 < pos < 1. For the undef handlign classes and
  functions, this is _required_.
*/

namespace Interpolate
{

template <class T>
inline T linearReg1D( T v0, T v1, float x )
{
    return x * v1 + (1-x) * v0;
}


template <class T>
inline T linearReg1DWithUdf( T v0, T v1, float x )
{
    if ( mIsUdf(v0) )
        return x < 0.5 ? mUdf(T) : v1;
    if ( mIsUdf(v1) )
        return x >= 0.5 ? mUdf(T) : v0;

    return linearReg1D( v0, v1, x );
}


template <class T>
inline T linear1D( float x0, T v0, float x1, T v1, float x )
{
    return v0 + (x-x0) * (v1-v0) / (x1-x0);
}

template <class iT>
inline iT linear1Di( float x0, iT v0, float x1, iT v1, float x )
{
    const float tmp = v0 + (x-x0) * (v1-v0) / (x1-x0);
    return mRounded( iT, tmp );
}



template <class T>
mClass(Algo) PolyReg1D
{
public:

PolyReg1D()
{
    set( 0, 0, 0, 0 );
}

PolyReg1D( const T* v )
{
    set( v[0], v[1], v[2], v[3] );
}

PolyReg1D( T vm1, T v0, T v1, T v2 )
{
    set( vm1, v0, v1, v2 );
}

inline void set( T vm1, T v0, T v1, T v2 )
{
    a_[0] = v0;
    a_[1] = v1 - (( 2*vm1 + 3*v0 + v2 ) / 6);
    a_[2] = (( v1 + vm1 ) / 2) - v0;
    a_[3] = (( v1 - vm1 ) / 2) - a_[1];
}

inline T apply( float x ) const
{
    const float xsq = x * x;
    return xsq * x * a_[3] + xsq * a_[2] + x * a_[1] + a_[0];
}

    T   a_[4];
};


template <class T>
inline T polyReg1D( T vm1, T v0, T v1, T v2, float x )
{
    return PolyReg1D<T>(vm1,v0,v1,v2).apply( x );
}


template <class T>
mClass(Algo) PolyReg1DWithUdf
{
public:

PolyReg1DWithUdf()      
{ set ( 0, 0, 0, 0 ); }

PolyReg1DWithUdf( const T* v )
{
    set( v[0], v[1], v[2], v[3] );
}

PolyReg1DWithUdf( T vm1, T v0, T v1, T v2 )
{
    set( vm1, v0, v1, v2 );
}

inline void set( T vm1, T v0, T v1, T v2 )
{
    v0udf_ = mIsUdf(v0); v1udf_ = mIsUdf(v1);
    if ( v0udf_ && v1udf_ ) return;

    if ( mIsUdf(vm1) ) vm1 = v0udf_ ? v1 : v0;
    if ( mIsUdf(v2) ) v2 = v1udf_ ? v0 : v1;
    if ( v0udf_ ) v0 = vm1;
    if ( v1udf_ ) v1 = v2;

    intp_.set( vm1, v0, v1, v2 );
}

inline T apply( float x ) const
{
    if ( (v0udf_ && x < 0.5) || (v1udf_ && x >= 0.5) )
        return mUdf(T);
    return intp_.apply( x );
}

    PolyReg1D<T>        intp_;
    bool                v0udf_;
    bool                v1udf_;

};

template <class T>
inline T polyReg1DWithUdf( T vm1, T v0, T v1, T v2, float x )
{
    return PolyReg1DWithUdf<T>(vm1,v0,v1,v2).apply( x );
}


template <class T>
inline T parabolic1D( float x0, T v0, float x1, T v1, float x2, T v2, float x )
{
    float xx0 = x - x0, xx1 = x-x1, xx2 = x-x2;
    return      v0 * xx1 * xx2 / ((x0 - x1) * (x0 - x2)) +
                v1 * xx0 * xx2 / ((x1 - x0) * (x1 - x2)) +
                v2 * xx0 * xx1 / ((x2 - x0) * (x2 - x1));
}


template <class T>
inline T poly1D( float x0, T v0, float x1, T v1, float x2, T v2,
                 float x3, T v3, float x )
{
    float xx0 = x - x0, xx1 = x-x1, xx2 = x-x2, xx3 = x-x3;
    return      v0 * xx1 * xx2 * xx3 / ((x0 - x1) * (x0 - x2) * (x0 - x3)) +
                v1 * xx0 * xx2 * xx3 / ((x1 - x0) * (x1 - x2) * (x1 - x3)) +
                v2 * xx0 * xx1 * xx3 / ((x2 - x0) * (x2 - x1) * (x2 - x3)) +
                v3 * xx0 * xx1 * xx2 / ((x3 - x0) * (x3 - x1) * (x3 - x2));
}


template <class T>
inline T predictAtZero1D( T vm2, T vm1, T v1, T v2 )
{
    return (-2 * vm2 + 8 * vm1 + 8 * v1 - 2 * v2) / 12;
}


template <class T>
inline T predictAtZero1D( T vm3, T vm2, T vm1, T v1, T v2, T v3 )
{
    return (vm3 - 6 * vm2 + 15 * vm1 + 15 * v1 - 6 * v2 + v3) / 20;
}


} // namespace Interpolate