Better msg implementation for random, complicated shape in 2D

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I want to design a .msg that represents a line with irregular shape. What would be the best optimal option especially utilizing existing ROS msg types as much as possible? Example image:

(Image obtained from http://www.had2know.com/images/irregshap.jpg)

The line like red curvy one in this figure is my target. For now, whether the line draws a cycle can be ignored for my purpose (to represent non-cyclic line is another design discussion).

My idea is:

geometry_msgs/Point[] dotsOnLine
# The order of Point objects in the array can be determined by certain algorithm. Not a focus in this discussion.

I found sensor_msgs/RegionOfInterest might be a good fit for rectangular/squares, but I guess not for irregular shapes. I'm asking particularly because I'm afraid I might be missing good existing msg types (I've only looked at common_msgs).