how to make inner loop in image.

hello everyone i have one edge of image and its centroid point i have the value of that edge pixel now i have to make a loop from that edge to centroid pixel. now what is the main thing, i have to find the another edge which is exactly under thae first edge and loop should be run till the centroid point.

[Image Analyst]

Huh? Can you put in some punctuation or have a better English speaker proofread this, or post a diagram, because I can't figure out what you're trying to ask at all despite reading it several times.