From: J. Forster (jfor@quik.com)
Date: Wed Dec 21 2005 - 10:10:48 PST
That was the point I was trying to make earlier. The bottom line is that, while
commercial units may read out to 1 foot, their absolute accuracy is just not
that good. If you want to drop a small bomb on a target, you have to know
exactly where that target is. It's NOT like asking how far to the nearest Burger
King.
Try taking one to a USGS accurately surveyed benchmark (there are lots of them,
marked on topo maps) and compare what the GPS reads with what is on the
benchmark.. Even with SA (selective availability) turned off you will be lucky
to be within 10 feet.
In vehicles, the nav systems APPEAR to do better, but they use other inputs in
addition to GPS (wheel info from ABS, solid state directional gyros, etc.).
Also, the mapping displays may assume you are on a road in their data base.
Bottom line, the nav systems are not good enough for serious surveying. The
survey systems are really differential... they compare the location of the
survey instrument to a 'reference' instrument located in the area. Sometimes
this comparison is done in real time via radio, sometimes by post processing.
-John
Cliff S 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
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