TriLinearInterpolator.cpp

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/* 
 *  Copyright (c) 2012, Chris Rogers
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#include "Fields/Interpolation/TriLinearInterpolator.h"
 
namespace interpolation {
 
TriLinearInterpolator::TriLinearInterpolator(const TriLinearInterpolator& lhs):
  Interpolator3dGridTo1d(lhs)
{
    coordinates_m = new ThreeDGrid(*lhs.coordinates_m);
    f_m = new double**[coordinates_m->xSize()];
    for (int i = 0; i < coordinates_m->xSize(); i++) {
        f_m[i] = new double*[coordinates_m->ySize()];
        for (int j = 0; j < coordinates_m->ySize(); j++) {
            f_m[i][j] = new double[coordinates_m->zSize()];
            for (int k = 0; k < coordinates_m->zSize(); k++)
                f_m[i][j][k] = lhs.f_m[i][j][k];
        }
    }
    coordinates_m->add(this);
}
 
void TriLinearInterpolator::function
                                (const double Point[3], double Value[1]) const {
    int i, j, k;  // position indices
    coordinates_m->lowerBound(Point[0], i, Point[1], j, Point[2], k);
    // bound checking
    if (i + 2 > coordinates_m->xSize() ||
        j + 2 > coordinates_m->ySize() ||
        k + 2 > coordinates_m->zSize()) {
        Value[0] = 0;
        return;
    }
    if (i  < 0 || j < 0 || k < 0) {
        Value[0] = 0;
        return;
    }
    // interpolation in x
    double dx = (Point[0]-coordinates_m->x(i+1))/
                (coordinates_m->x(i+2)-coordinates_m->x(i+1));
    double f_x[2][2];
    f_x[0][0] = (f_m[i+1][j]  [k]   - f_m[i][j]  [k])   * dx + f_m[i][j]  [k];
    f_x[1][0] = (f_m[i+1][j+1][k]   - f_m[i][j+1][k])   * dx + f_m[i][j+1][k];
    f_x[0][1] = (f_m[i+1][j]  [k+1] - f_m[i][j]  [k+1]) * dx + f_m[i][j]  [k+1];
    f_x[1][1] = (f_m[i+1][j+1][k+1] - f_m[i][j+1][k+1]) * dx + f_m[i][j+1][k+1];
    // interpolation in y
    double f_xy[2];
    double dy = (Point[1]-coordinates_m->y(j+1))/
                (coordinates_m->y(j+2) - coordinates_m->y(j+1));
    f_xy[0] = (f_x[1][0] - f_x[0][0])*dy + f_x[0][0];
    f_xy[1] = (f_x[1][1] - f_x[0][1])*dy + f_x[0][1];
    // interpolation in z
    Value[0]  = (f_xy[1] - f_xy[0])/
                (coordinates_m->z(k+2) - coordinates_m->z(k+1))*
                (Point[2] - coordinates_m->z(k+1)) + f_xy[0];
}
}