[zeshkani]

what would be the order n of principal rotation, and Cn on the Butterfiles image from M.C. Escher

[Dan]

Why didn't you post a picture? I it this one?

After 30 posts you should be aware of the forum rules and abide by them.

[zeshkani]

this is the picture

[Yggdrasil]

Here's how I would determine the rotation axis of the image.  Look for a distinct pattern that repeats itself around the center of the image.  For example, notice the yellow and orange circles near the midpoint of a radius of the image.  If you rotate the image, you will see that these circles will line up, along with everything else in the image (discounting coloration).  So, if you count these features, you should get the order of your rotation axis.