Length of convexity

[[Ta...]]

Dear Programmers,

I am looking for a CMM measuring solution for ground outer diameter measurement. Requirements are the follows: 
- Konvex 0,003-0,006mm 
-Length of convexity is 20±1mm. Simmetric on 30mm long cilinder length

Question is the length measurement opportunity.

If do anybody has solution for this, please share with me.  

Thanks in advance

[[Ow...]]

Could you share a drawing (partial drawing or clipped section) or hand drawn sketch of the feature and its datum's being measured to help up understand what you are trying to measure?

If it is a crown or diametral relief on the cylinder, a best fit curve or line section may be the solution.