main/src/georegression/metric/Distance2D_F64.java
public static double distanceSq( Quadrilateral_F64 quad , Point2D_F64 p ) {
		LineSegment2D_F64 seg = LineSegment2D_F64.wrap(quad.a, quad.b);
		double a = distanceSq(seg, p);
		seg.a = quad.b;seg.b = quad.c;
		a = Math.min(a,distanceSq(seg,p));
		seg.a = quad.c;seg.b = quad.d;
		a = Math.min(a,distanceSq(seg,p));
		seg.a = quad.d;seg.b = quad.a;
		return Math.min(a, distanceSq(seg, p));
	}
public static double distanceSq( Quadrilateral_F64 quad , Point2D_F64 p ) {
		LineSegment2D_F64 seg = LineSegment2D_F64.wrap(quad.a, quad.b);
		double a = distanceSq(seg, p);
		seg.a = quad.b;seg.b = quad.c;
		a = Math.min(a,distanceSq(seg,p));
		seg.a = quad.c;seg.b = quad.d;
		a = Math.min(a,distanceSq(seg,p));
		seg.a = quad.d;seg.b = quad.a;
		return Math.min(a, distanceSq(seg, p));
	}
Returns the Euclidean distance squared of the closest point on the quadrilateral to the provided point.

@param quad Quadrilateral
@param p Point
@return Distance squared apart