polygon_area
NOTE: Be sure to use the absolute value of the return for the true area of the polygon.
)
The area of a simple concave polygon is one half the sum of the cross products of the adjacent edges. The sign of the result indicates the winding of the polygon, clockwise or counter-clockwise. Holes can be accounted for if the winding of the hole edges is the reverse of the perimeter edges.
polygon_area(polygon) Returns the area of a given polygon.
/*
** Usage:
** polygon_area(polygon)
**
** Description:
** Takes a list of points defining the boundary of a polygon
** and returns the area enclosed within.
**
** Arguments:
** polygon ds_list containing XY coordinate pairs defining
** the shape of a polygon {x0,y0,x1,y1,...,xn,yn}
**
** Returns:
** area area of the polygon, if negative the polygon is
** clockwise
**
** Notes:
** Polygons are closed figures, the first point in the polygon
** will also be considered the last point in the polygon.
** Polygons must be simple, which means they can not have
** edges that cross each other.
**
** Example:
** in: polygon = {100,100,100,200,200,200,200,100}
** (a square polygon with corners at 100,100 and 200,200)
** out: 10000
**
** GMLscripts.com
*/
{
var a,i,j,x1,y1,x2,y2;
a = 0;
j = ds_list_size(polygon);
for (i=0; i<j div 2; i+=1) {
x1 = ds_list_find_value(polygon,(2*i) mod j);
y1 = ds_list_find_value(polygon,(2*i+1) mod j);
x2 = ds_list_find_value(polygon,(2*i+2) mod j);
y2 = ds_list_find_value(polygon,(2*i+3) mod j);
a += x1*y2 - x2*y1;
}
return a / 2;
}
** Usage:
** polygon_area(polygon)
**
** Description:
** Takes a list of points defining the boundary of a polygon
** and returns the area enclosed within.
**
** Arguments:
** polygon ds_list containing XY coordinate pairs defining
** the shape of a polygon {x0,y0,x1,y1,...,xn,yn}
**
** Returns:
** area area of the polygon, if negative the polygon is
** clockwise
**
** Notes:
** Polygons are closed figures, the first point in the polygon
** will also be considered the last point in the polygon.
** Polygons must be simple, which means they can not have
** edges that cross each other.
**
** Example:
** in: polygon = {100,100,100,200,200,200,200,100}
** (a square polygon with corners at 100,100 and 200,200)
** out: 10000
**
** GMLscripts.com
*/
{
var a,i,j,x1,y1,x2,y2;
a = 0;
j = ds_list_size(polygon);
for (i=0; i<j div 2; i+=1) {
x1 = ds_list_find_value(polygon,(2*i) mod j);
y1 = ds_list_find_value(polygon,(2*i+1) mod j);
x2 = ds_list_find_value(polygon,(2*i+2) mod j);
y2 = ds_list_find_value(polygon,(2*i+3) mod j);
a += x1*y2 - x2*y1;
}
return a / 2;
}
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Projects: 8
Related: angle_difference, is_clockwise, line_get_slope, lines_intersect, normal_detect, point_in_circle, point_in_polygon, point_in_triangle, polygon_area, polygon_centroid
Contributor: xot
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