freebeer
thanks, will try to educate myself.
as far as an angular offset, I was thinking that over such a relatively short distance, 5 angular seconds would likely be excessive precision.
Wish I could do mental calculations still, as to how much distance a second of arc on the earth's surface is, then scale that from the earth's radius down to distances seen here.
I believe I've read that the internal OSM resolution is about a centimetre on the ground, depending where one is, as a typical worst-case value.
oh well, I'll stop musing aloud.  If the customer is satisfied, no need to split hairs...
thanks!