Vertical displacement speed

Does anybody know if a unit will use the vertical displacement in the
speed calculation? Or is it a simple change in latitude/longitude
that is used? For example, if you were in an elevator (and had a
signal) would the vertical rate of travel be correctly calculated?

Your speed readout wont take into account any vertical velocity. Your GPS
uses a "here I am, there I was" kind of calculation to determine horizontal
position, utilizing 3 satellites (2 for horizontal triangulation, the third
as a time keeper). Altitude readout needs 4 satellites, the 3 same as
before, and a 4th to couple with one of the other 2 to get an altitude
calculation. So, if you're travelling up or down a slope, you're speed
readout on your GPS will be slightly slower than your actual ground speed.
It's not a significant difference. As an aircraft maintenance engineer,
I've seen a 3 to 4 knot difference between the calibrated airspeed and the
readout on the Garmin G1000 during a 1400 feet per minute climb, which is no
where near as fast of vertical speed as any normal car will go.

Actually, I am trying to determine my speed while skiing where some
slopes are very steep and the vertical component might be rather
significant. On a 45 degree slope, the hypotenuse is about 1.41 times
as long. Today, my max speed on my Garmin (60csx) was 37.2 mph which
would be more like 52 mph if it were on a 45 degree slope (which is
not unusual).

wrote:

GPS calculates speed as true distance between two signal points divided by
time between those points traveled. This is true speed and not horizontal
speed. My GPS shows the same speed as my car regardless traveling up, down
or horizontal.

Jan

Jan Nademlejnsky wrote:

If you were maintaining a steady ground speed, I would think it would
actually display a slower speed as you traveled up a hill and down the
other side.