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];
    }
}  // namespace interpolation