"Travis Marlatte" wrote:

"Marco Leon" wrote in message
oups.com...
When we look at a GPS error value in a so-equipped GPS, does that value
reflect *both* the vertical (i.e. altitude) and the horizontal
component? Can a separate value for each be determined?

The reason I ask is that in firing up my Garmin 496 (an early Christmas
present, comments to follow in another post ), I noticed the altitude
initially register at 100 ft below actual then right itself after a few
minutes. All of this happened while the horizontal location did not
noticeably move (had it fully-zoom by the way) which led me to believe
that the error can be different from each other at least initially.

Marco


They have separate error characteristics and separate error indicators -
although they are dependent. Typically, if a GPS unit displays any kind of
error value, it is for the horizontal component simply because that is what
most users will want to see. It is most likely an interpretation of the
statistical error in units of meters or feet. The statistical error is
called dilution of position and most GPS receivers determine an HDOP, a
VDOP, and a couple of others.
---------------------
Travis
Lake N3094P
PWK

Actually the DOPs are related to satellite geometry and are unitless.
It is only when you multiply the DOP by the signal/user equipment
error that you get some sort of error in feet/meters.

Ron Lee