sql server - Similarity between line strings -

i have number of tracks recorded gps, more formally can described number of line strings.

now, of recorded tracks might recordings of same route, because of inaccurasies in gps system, fact recordings made on separate occasions , might have been recorded travelling @ different speeds, won't match perfectly, still close enough when viewed on map human determine it's same route has been recorded.

i want find algorithm calculates similarity between 2 line strings. have come home grown methods this, know if problem that's has algorithms solve it.

how calculate similarity, given similar means represents same path on map?

edit: unsure of i'm talking about, please @ link definition of line string is: http://msdn.microsoft.com/en-us/library/bb895372.aspx - i'm not asking character strings.

compute fréchet distance on each pair of tracks. distance can used gauge similarity of tracks.

math alert: fréchet pioneer in field of metric space relevant problem.