Distance of a curve for a shade sail

[Smokey dan]

Hey Guys I have no idea how to work out the exact distance of the perimeter of my shade sail.
I need to work out this problem so I can purchase some led lights that run the perimeter of the the shade sail for my business.
I know you probably don't live near my business but if you are ever in the area I would happily shout you a dinner at my restaurant for your help.
Anyway.
The distant between the posts is givin in the drawing also the distance of the centre of the curve to the centre of the post span is given.
You will also need to add on an additional 100mm to each distance between posts to allow for tensioning.

Thanks heaps guys.