uk.ac.rdg.resc.edal.graphics.utils.BilinearInterpolator Maven / Gradle / Ivy

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package uk.ac.rdg.resc.edal.graphics.utils;

import java.util.List;

public class BilinearInterpolator {
    private List xVals;
    private List yVals;
    private double[][] data;
    
    private double[] xRanges;
    private double[] yRanges;

    public BilinearInterpolator(List xVals, List yVals, double[][] data) {
        this.xVals = xVals;
        this.yVals = yVals;
        this.data = data;
        
        xRanges = new double[xVals.size()];
        yRanges = new double[yVals.size()];
        
        for(int i=1; i < xVals.size(); i++) {
            xRanges[i] = xVals.get(i) - xVals.get(i-1);
        }
        for(int i=1; i < yVals.size(); i++) {
            yRanges[i] = yVals.get(i) - yVals.get(i-1);
        }
    }
    
    public double getValue(double x, double y) {
        /*
         * Find the indices above the x and y values  
         */
        int xIndex = 0;
        int yIndex = 0;
        while(xVals.get(xIndex) <= x && xIndex < xVals.size() - 1) {
            xIndex++;
        }
        while(yVals.get(yIndex) <= y && yIndex < yVals.size() - 1) {
            yIndex++;
        }
        double xFAlong;
        double yFAlong;
        if(xIndex == 0) {
            xIndex++;
            xFAlong = 1.0;
        } else {
            xFAlong = (x - xVals.get(xIndex - 1)) / xRanges[xIndex];
        }
        if(yIndex == 0) {
            yIndex++;
            yFAlong = 1.0;
        } else {
            yFAlong = (y - yVals.get(yIndex - 1)) / yRanges[yIndex];
        }
        
        return 
                xFAlong * yFAlong * data[xIndex][yIndex] +
                xFAlong * (1.0-yFAlong) * data[xIndex][yIndex-1] +
                (1.0-xFAlong) * yFAlong * data[xIndex-1][yIndex] +
                (1.0-xFAlong) * (1.0-yFAlong) * data[xIndex-1][yIndex-1];
    }
}