function getDistance(p1, p2, props) {
	    if (!props) {
	        props = PROPS_XY;
	    }
	    var x = p2[props[0]] - p1[props[0]],
	        y = p2[props[1]] - p1[props[1]];
	
	    return Math.sqrt((x * x) + (y * y));
	}
calculate the absolute distance between two points
@param {Object} p1 {x, y}
@param {Object} p2 {x, y}
@param {Array} [props] containing x and y keys
@return {Number} distance