main/src/georegression/geometry/UtilPolygons2D_I32.java
public static boolean isConvex( Polygon2D_I32 poly ) {
		// if the cross product of all consecutive triples is positive or negative then it is convex

		final int N = poly.size();
		int numPositive = 0;
		for (int i = 0; i < N; i++) {
			int j = (i+1)%N;
			int k = (i+2)%N;

			Point2D_I32 a = poly.vertexes.data[i];
			Point2D_I32 b = poly.vertexes.data[j];
			Point2D_I32 c = poly.vertexes.data[k];

			int dx0 = a.x-b.x;
			int dy0 = a.y-b.y;

			int dx1 = c.x-b.x;
			int dy1 = c.y-b.y;

			int z = dx0 * dy1 - dy0 * dx1;
			if( z > 0 )
				numPositive++;
			// z can be zero if there are duplicate points.
			// not sure if it should throw an exception if its "bad" or not
		}

		return( numPositive == 0 || numPositive == N );
	}
public static boolean isConvex( Polygon2D_I32 poly ) {
		// if the cross product of all consecutive triples is positive or negative then it is convex

		final int N = poly.size();
		int numPositive = 0;
		for (int i = 0; i < N; i++) {
			int j = (i+1)%N;
			int k = (i+2)%N;

			Point2D_I32 a = poly.vertexes.data[i];
			Point2D_I32 b = poly.vertexes.data[j];
			Point2D_I32 c = poly.vertexes.data[k];

			int dx0 = a.x-b.x;
			int dy0 = a.y-b.y;

			int dx1 = c.x-b.x;
			int dy1 = c.y-b.y;

			int z = dx0 * dy1 - dy0 * dx1;
			if( z > 0 )
				numPositive++;
			// z can be zero if there are duplicate points.
			// not sure if it should throw an exception if its "bad" or not
		}

		return( numPositive == 0 || numPositive == N );
	}
Determines if the polugon is convex or concave.

@param poly Polygon
@return true if convex and false if concave