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

My background idea is to create a software layer that m开发者_如何转开发erges 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

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.