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I want a java function where if we pass the lat,long of a object, whether that object lies inside a area. Again this Area is defined by lat,long

for example I define a area with 3 lat/long positions.( a rectangle ) and if I pass a lat/long position it should return me whether its within the rectangle.

trashgod
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user2771655
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  • sounds easy, what have you done so far? – kai Feb 06 '14 at 09:57
  • Have a look at [this question](http://stackoverflow.com/questions/4287780/detecting-whether-a-gps-coordinate-falls-within-a-polygon-on-a-map), especially the linked framework. – Daniel Feb 06 '14 at 09:58

1 Answers1

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If the area is always a rectangle, the easiest way is to compare the coordinates.

Let's assume that your rectangle is defined by its upper left (r1x: lon and r1y: lat) and lower right (r2x and r2y) corners. Your object (a point) is defined by px: lon and py: lat.

So, your object is inside the area if

px > r1x and px < r2x

and

py < r1y and py > r2y

Programatically it would be something like:

boolean isPInR(double px, double py, double r1x, double r1y, double r2x, double r2y){

if(px > r1x && px < r2x && py < r1y && py > r2y){
    //It is inside
    return true;
}
    return false;
}

EDIT

In the case where your polygon is not a rectangle, you can use the Java.awt.Polygon Class. In this class you will find the method contains(x,y) which return true if the point with x and y coordinates is inside the Polygon. This method uses the Ray-casting algorithm. To simplify, this algorithm draw a segment in a random direction from your point. If the segment cross your polygon's boarder an odd number of times, then it is inside your polygon. If it crosses it an even number of times, then it is outside.

The ray-casting algorithm (simple)

To use the polygon Class, you can do something like:

//This defines your polygon
int xCoord[] = {1,2,3,5,9,-5};
int yCoord[] = {18,-32,1,100,-100,0};

myPolygon = new Polygon(xCoord, yCoord, xCoord.length);

//This finds if the points defined by x and y coordinates is inside the polygon
Boolean isInside = myPolygon.contains(x,y);

And don't forget to

import java.awt.Polygon;

EDIT

Right coordinates are in Double !

So you need to use Path2D.Double !

Begin by import java.awt.geom.Path2D;

Let's say you start with similar arrays as before:

//This defines your polygon
Double xCoord[] = {1.00121,2,3.5464,5,9,-5};
Double yCoord[] = {18.147,-32,1,100,-100.32,0};

Path2D myPolygon = new Path2D.Double();

//Here you append all of your points to the polygon
for(int i = 0; i < xCoord.length; i++) {
    myPolygon.moveTo(xCoord[i], yCoord[i]);
}
myPolygon.closePath();

//Now we want to know if the point x, y is inside the Polygon:
Double x; //The x coord
Double y; //The y coord
Boolean isInside = myPolygon.contains(x,y);

And here you go with Double !

Legisey
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