WAAS question -- altitude accuracy?

steve writes:

Doesn't the GPS give you 'altitude' -- computed as height above the
surface of an ellipsoid? Or does it correct for mean sea level? There
seem to be several computations required to derive true altitude from
the raw GPS altitude coordinate and it is not clear to me if
particular GPS receivers perform this adjustment.

I think that most of them use WGS84, which is a little more complex
than a simple ellipsoid.


All the best,


David

"David Megginson" wrote in message
...
steve writes:

Doesn't the GPS give you 'altitude' -- computed as height above the
surface of an ellipsoid? Or does it correct for mean sea level? There
seem to be several computations required to derive true altitude from
the raw GPS altitude coordinate and it is not clear to me if
particular GPS receivers perform this adjustment.

I think that most of them use WGS84, which is a little more complex
than a simple ellipsoid.

Some models (Garmin's included) display orthometric (above the geoide or
roughly above mean sea level) by using a look up table for the geode height,
and some other models display the ellipsoid altitude.

"David L. Wilson" wrote in message
t...
"David Megginson" wrote in message
...
steve writes:

Doesn't the GPS give you 'altitude' -- computed as height above the
surface of an ellipsoid? Or does it correct for mean sea level? There
seem to be several computations required to derive true altitude from
the raw GPS altitude coordinate and it is not clear to me if
particular GPS receivers perform this adjustment.

I think that most of them use WGS84, which is a little more complex
than a simple ellipsoid.

Some models (Garmin's included) display orthometric (above the geoide or
roughly above mean sea level) by using a look up table for the geode
height,
and some other models display the ellipsoid altitude.

And it should also be injected into this thread that Delta won't be doing
blind approaches with SP IIIs. As has been pointed out in many, many
threads, there's GPSRs, and there's GPSRs, and that second set has 2 or
three more zeros on the end.

Frank

"Frank Looper" wrote in message
...


And it should also be injected into this thread that Delta won't be doing
blind approaches with SP IIIs. As has been pointed out in many, many
threads, there's GPSRs, and there's GPSRs, and that second set has 2 or
three more zeros on the end.

Frank


The accuracy is the same though.

Mike
MU-2

"Mike Rapoport" wrote in message
k.net...

"Frank Looper" wrote in message
...


And it should also be injected into this thread that Delta won't be
doing
blind approaches with SP IIIs. As has been pointed out in many, many
threads, there's GPSRs, and there's GPSRs, and that second set has 2 or
three more zeros on the end.

Frank


The accuracy is the same though.

Mike
MU-2

There are a number of people who would disagree with you on that, and most
likely not just folks who sell those five figures units, but their customers
and others as well.

Frank