Getting the higher resolutions on GPS

From: J (W7LS@blarg.net)
Date: Wed Dec 21 2005 - 13:53:49 PST

One simple trick some GPS use is just plain old averaging positions over
time. If you just sit there and average all the positions the GPS says
over a long time, like hours, you can get down to a few millimeters.
Surveyors have this kind of equipment. Any one given GPS coordinate
reading is prone to the adversities of the atmosphere, and the users
position will appear to wander about, in a 10 meter area. Over time,
your true position will be in the center of all that wandering. Jim

Bill Kealey wrote:

>
>
>> I sure would like to know where you all are getting the high speed
>> stuff to give such good coordinates........in the military (as I am
>> and have been for 18 years) we can only get as close as 10 feet. If
>> you all can send the updated codes I would gladly use them
>> ........then again I am a Marine and should probably check with the
>> AF or the Navy to get the good stuff......ours will probably come to
>> age when you all get the "new" stuff.
>>
>> ......but still wondering how you all get to 1 foot?????
>>
>>
>>
>> SSGT SMITH CN
>> USMC MITT, 1ST BN, 3RD BDE, 7TH DIV
>> NUMANIYAH
>> APO AE 09331
>>
>> M880, M274A5, 6K GenSet
>
>
>
>
> Cliff,
>
> I was always told that the best my unit could expect to do on a good
> day was about 3' or 1 meter. Playing around in the police boats and
> pilings that are usually considered "fixed objects" I found that the
> accuracy was, as you said more like 10' to 12' or approximately 3 meters.
>
> My GPS altitude readings are so far off that I have never found them
> to be useful to me. When I lived near and worked on Chesapeake Bay,
> altitude was never an issue. We didn't get any tsunamis that I recall
> so basically the tidal difference was all I had to adjust for and did
> not need GPS for that.
>
> I am now with the local fire department in the mountains and the
> altitude readings could be very helpful with Search and Rescue here
> with the use of topo maps. Again, the unit that I use shows it is
> rarely more accurate then within +/- 185 feet or so. I am situated in
> a valley between two small mountains with a third splitting them about
> a half mile or so from my home.
>
> I know that our engineering division used to have to hook up two
> antennas to the GPS and separate the antennas about 4 or 5 feet to get
> accuracy good enough to be useful in court and it did work. They were
> using the same Garmin 45 at that time that I use now. Again, that was
> at least 10 years ago so I know that the technology has improved quite
> a bit.
>
> I certainly would not want to use my GPS unit to do an accurate survey
> of my property line (or say, a mine field) but would have no problem
> using it as a reference tool.
>
> And, to put the accuracy in a different perspective, how much
> compensation does one allow for the width of a pencil point when
> locating your position on a map/chart? This can certainly open
> another can of worms as pencil points vary quite a bit depending on
> many factors such as, the sharpener used, how long between sharpenings
> you have been using it, diameter of lead used if a mechanical pencil
> and other things. We also have to compensate for the proportional
> size of the map/chart being used.
>
> So, IMHO, unless the GPS units are that much more accurate than what I
> have been using all these years I personally doubt that the units are
> normally as accurate as advertised. However, anything is possible.
>
>
> Have a great day.
>
> Bill K.
>
>
>
>
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