Java Distance Calculate distancePointToLine(final double x0, final double y0, final double x1, final double y1, final double xp, final double yp)

Description

Compute the distance of a point from a line.

License

Open Source License

Parameter

Parameter	Description
x0	x coordinate of P0 that defines the line
y0	y coordinate of P0 that defines the line
x1	x coordinate of P1 that defines the line
y1	y coordinate of P1 that defines the line
xp	x coordinate of point
yp	y coordinate of point

Return

distance between the line and the point.

Declaration

public static double distancePointToLine(final double x0, final double y0, final double x1, final double y1,
        final double xp, final double yp) 

Method Source Code

//package com.java2s;

public class Main {
    /**/*from  w  w  w  .j  a va2 s .  c  om*/
     * Compute the distance of a point from a line. Note that the line
     * is merely defined by the two points and continues to infinity
     * in both directions. So the projection of the point does
     * not have to lie within the two points (they are not the end points).  
     * 
     * @param x0 x coordinate of P0 that defines the line
     * @param y0 y coordinate of P0 that defines the line
     * @param x1 x coordinate of P1 that defines the line
     * @param y1 y coordinate of P1 that defines the line
     * @param xp x coordinate of point 
     * @param yp y coordinate of point
     * @return distance between the line and the point.
     */
    public static double distancePointToLine(final double x0, final double y0, final double x1, final double y1,
            final double xp, final double yp) {

        double[] pt = projectPointOntoLine(x0, y0, x1, y1, xp, yp);

        return Math.sqrt((pt[0] - xp) * (pt[0] - xp) + (pt[1] - yp) * (pt[1] - yp));
    }

    /**
     * Find the point on the line that is closest to the specified point. 
     * 
     * Equation of a line:
     * P = P0 + u(P1 - P0)
     * 
     * P2 is the point on the line that is closest to P
     * (P2-P) dot (P2-P1) = 0 
     * 
     * @param x0 x coordinate of P0 that defines the line
     * @param y0 y coordinate of P0 that defines the line
     * @param x1 x coordinate of P1 that defines the line
     * @param y1 y coordinate of P1 that defines the line
     * @param xp x coordinate of point 
     * @param yp y coordinate of point
     * @return an array containing the x,y coordinate of the closest point. 
     */
    public static double[] projectPointOntoLine(final double x0, final double y0, final double x1, final double y1,
            final double xp, final double yp) {

        double u = (xp - x0) * (x1 - x0) + (yp - y0) * (y1 - y0);
        u = u / ((x1 - x0) * (x1 - x0) + (y1 - y0) * (y1 - y0));

        // location of the point on the line where the tangent intersects
        double x = x0 + u * (x1 - x0);
        double y = y0 + u * (y1 - y0);

        return new double[] { x, y };
    }
}

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