Any ideas for a model (class diagram) to track visitors for a website?

Question

My background idea is to create a software layer that merges all the things related to anonymous visitors:
-uniqueness
-sessions
-geo-localization -hit counter
-basic reporting
-distributable APIs
-thermal map for forms
Many talk well about Piwik. I'm at the beginning of discovering process so I need to know if I have to reinvent the wheel or lay on the giants' shoulders.
PS: google analytics is an option as now

Answer 1

Piwik is definitely the way to go, the only thing it doesn't do is "-thermal map for forms" but the rest is covered, and more. Full featured API (For analytics reports & for tracking data), nice UI, etc.