A couple of Ooopsies
Received the following from N4GI
++++++++++++++++++++++++++++++++++++++++++++++++
> Anyway, when marking a position using averaging my unit claims to
> be, typically, within 12 ft or so of being right.
My 12 channel magellan 315 has +/- 100' resolution. This is about
average.
I use differentially corrected GPS and WAAS for my work (they
receive a
radio beacon), and those can get to about +/- 15' resolution. The
surveyor's Trimble units ($7,500) can get down to sub-meter
positioning. I
would NOT use a regular hand held GPS to do surveying, they are
only good if
you are lost in the woods!!!
73,
Blake N4GI
++++++++++++++++++++++++++++++++++++++
Hmmm..... Well, maybe it's still OK for relative measurements.
I'll try a couple of things and post the results.
> one. How do you do this? I don't remember but there must be many
> places on the web that will tell you how. The distances are so
> small that I can't imagine that you would have to use spherical
> trig. As I recall, one minute of latitude or longitude is 1
> nautical mile or 6080 ft. If I'm wrong, I hope someone will
> correct me.
>
Well, I'm wrong. A quick look at a globe (in daylight as opposed
to 3 am) shows that lines of longitude get closer to each other as
you move away from the equator.
So, who's going to give us the info needed to calculate lat and
long for a position given bearing and distance from a known
position for the distances and accuracy that Tom needs? I would
think that just being able to calculate the circumference of the
earth at a particular latitude would give us everything we need.
Of course, if Blake is right about GPS accuracy, none of the rest
matters. I'll use my GPS to measure the lat and long of a fixed
point over a period of time and see how much it wanders. (Hmm..
let's see now, connect GPS to computer with serial cable, write a
program to poll the GPS every ten minutes, write the results to a
file... Maybe I'll just do it once an hour and write the results
on a piece of paper.)
>
> 73 & Happy New Year de Jim Smith VE7FO
>
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