Let me preface this by saying: awesome idea, go for it!Any other ideas? Are there any apps out there which already do something similar?
Sounds not unlike some of my long term goals for my pet project, which I was interviewed about here: [media]http://www.youtube.com/watch?v=_WeWBXRXUog[/media]
If you want to actually take a look at what I've done, I *started* some of this in the "analysis" folder in src/ in obdgpslogger's svn. Never got very far with it as I ran out of time. I started by calculating mpg per trip, and then I started working on grouping trips by start, end locations and time of day.
I always imagined at the very least, a box and whisker plot for each different path to/from work would be good, which might also need to be organised by time. My theory is that it would look something like this [note the lower average but higher variance and massively higher outliers on the freeway. Boxes and averages are roughly the same in my drawing, that almost certainly won't be the case]:
There are OBD PIDs for "load", which are probably what you want. Current gear is harder to accurately arbitrarily figure than you think, unless you can find a PID for it [will be manufacturer-specific, as there isn't a generic one]. Here's an example graph of vehicle speed divided by RPM [the graph-wide "flat bits" map to gear, with the lowest being first]:
Admittedly this is mainly C with some C++, not Java, but it might give you some ideas. I have actually just got an Android phone, so now I'm considering porting my stuff.
If you want some sample data sets to look at, http://icculus.org/obdgpslogger/examples/longterm... man, that's way out of date. Look again later today, I'll try to upload the current version if I can. Be warned that there's a lot of datapoints there, google earth hurts opening the KML if you don't have generous amounts of memory. But you can extract stuff manually from the .db, it's a simple sqlite3 database [or download and build obdgpslogger, which has an obd2csv tool].