From: Johnlebl@aol.com
Date: Fri Jul 19 2002 - 11:18:21 CDT
In a message dated 07/19/2002 8:59:20 AM Central Daylight Time,
ahamm@alanhamm.com writes:
> So I wonder.........if I go into the setup on my gps and change the datum to
> NAD27, will the plotted waypoints magically pop into the right locations
> based on the exact grid points that I did locate. I might try this.
>
The answer is a resounding NO. It should but it doesn't work that way. Each
time you do this the instrument re-rounds them off and they change. Your GPS
stores all data in one particular datum and it simply converts it to the
datum you set it for and that it displays on the screen.
If you put data in that is NAD27 and your GPS is set for WGS80, then it
converts what actually is NAD27 to WGS80 and then when you change the
settings it recalculates it again to what it thinks is correct. What you get
is a creaping of the location farther and farther from the point it actually
is. Until you figure out what is actually happening this is a very
frustrating situation.
The bottom line on GPS use is they are extremely accurate when the instrument
collects the data of a waypoint from where you are on the earth's surface.
However, when one tries to enter waypoint data from other sources such as
read from a map or gained from a friend, all sorts of errors are compounded.
Reliable sources gains a complete new meaning when using a GPS.
John LeBlanc
Eagle Class of 1959
Phirst Phil Ptrek 1959
PhilTrek 2002 630H2 Trek 16
My latest adventure was yesterday,
Today is not over yet!
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