main/src/georegression/metric/Area2D_F64.java
public static double triangle( Point2D_F64 a, Point2D_F64 b, Point2D_F64  c ) {
		double inner = a.x*(b.y - c.y) + b.x*(c.y - a.y) + c.x*(a.y - b.y);

		return Math.abs(inner/2.0);
	}
public static double triangle( Point2D_F64 a, Point2D_F64 b, Point2D_F64  c ) {
		double inner = a.x*(b.y - c.y) + b.x*(c.y - a.y) + c.x*(a.y - b.y);

		return Math.abs(inner/2.0);
	}
Computes the area of an arbitrary triangle from 3-vertices.

area = | a.x*(b.y - c.y) + b.x*(c.y - a.y) + c.x*(a.y - b.y) | / 2

@param a Corner point 1
@param b Corner point 2
@param c Corner point 3
@return area