CODEWITHSUNDEEP
javageometrypoint
Totalllyrandomguy
Totalllyrandomguy

Reputation: 149

find point of intersection between line and altitude

I am trying to find the point of intersection between a line the altitude of a point to that line. So given the information, two points that create a line and one point to draw the altitude from, I want to find the point on the line that is closest to the point, (so a point on the line that forms a perpendicular line with the given point.)

(hope that made sense without an illistration)

given a line and a point, how would I find this new Point?

public static Point2D findPointOnTwoLines(Line2D line, Point2D point) {
    double slope = line.getSlope();
    double oppRec = line.getOppRecip(); // returns the opposite reciprocal of the slope
    double x = ((slope * line.getPoint1().getX()) - (line.getPoint1().getY())) 
            / ((slope) - (oppRec));
    double y = (slope * ((oppRec * point.getX()) - point.getY())) - (oppRec * ((slope * point.getX()) - point.getY()))
            / ((slope) - (oppRec));

    return new Point2D(x, y);
}

this is my attempt at solving the equation using determinents, and it failed to give the right coordinate when I passed:

Line2D line = new Line2D(2, 3, 1, 1); // line from (2, 3) to (1, 1)
Point2D point = new Point2D(0, 2);

if you know how to find the right point using this method, (or any other method for that matter) it would be greatly appreciated!!

ASKII art of what I mean, if you can make a real image of this and send it to me I would be happy to use that instead.

1
 \       3
  \     /    
   \   /      the number points are thrown in as arguments, and the "X" point is returned
    \ /
     X    <---- this is a 90 degree angle
      \
       \        the "X" is suppose to represent the point on the line closest to the point "3"
        \
         2

Upvotes: 0

Views: 326

Answers (1)

Paul Boddington
Paul Boddington

Reputation: 37645

double x = (point.getY() - oppRec * point.getX() - line.getPoint1().getY() + slope * line.getPoint1().getX()) / (slope - oppRec);
double y = oppRec * x + point.getY() - oppRec * point.getX();

Upvotes: 1

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