Hopscotch

WOW, what a stack of juvenile spew! In the midst of all this useless crap, I'd like to thank Hiemdahl for discussing actual time-of-day factors that affect GPS accuracy. I had assumed that the only time-of-day factors were heat-driven humidity changes and normal daily atmospheric dilation, but this is obviously incorrect. Everybody else (except Peter) has confused satellite geometry with unrelated factors, and thus provided no useful info.

We use Trimbles at work, where precision is a requirement, and as long as the PDOP is under 4 and we've got >1 hour of averaging, we're satisfied. Using the Trimble Planning Software (as mentioned by Johnnyvegas) and some back-calculating, I learned the PDOP never got above 6 when my Meridian reported the curb moved 34' in 2 hours. I'm disappointed in that magnitude of error, but I guess I'll learn to live with it - and keep the Trimble's batteries charged, just in case. I've learned that satellite configuration (which is independant of the local time of day) can produce an error of six or so inches for the Trimble, so I guess I'll have to do some side-by-side comparisons to find how bad the error can get for the Meridian.

I had problems with accuracy today even though I left the unit on continuously. While looking for a cache (and eating lunch) I left the unit sitting on the curb next to the suspected cache location for fifteen minutes to average out. This is in a dead-flat parking lot, in the middle of five miles of dead-flat farmland, with 4 to 7 satellites showing on the status screen. I got to within one foot of the cache location, but couldn't find it. Two hours later, I put the unit back on the same spot on the curb, left it there for another fifteen minutes with 5 to 9 satellites showing, and found the curb had moved 34 feet! What's going on here? I had wide-open sky, 15 minutes of averaging, lots of satellites, and the curb moves? Any tips on how to get consistent readings would be appreciated.