----- Original Message -----
Sent: Sunday, February 13, 2011 4:54
PM
Subject: Re: [PSUBS-MAILIST]
Navigation
Yes - as long as you know the system state when the IMU is
activated, then you can use the IMU output to determine the current
state. The IMU only measures acceleration directly, but if your
ship is floating with the current, you can get both the initial position and
the initial velocity from the GPS. Using both of those values as the
startup state, the IMU can provide corrections from then on. Whenever
you have a valid GPS fix, you would re-initialize the internal velocity and
position to that reported by the GPS in order to eliminate the accumulated
errors, "resetting the clock", so to speak. (Incidentally, GPS is
actually more accurate in velocity than it is in position. This makes
sense if you think about how a GPS receiver actually works.) Similarly,
using a Doppler sonar when near the bottom will solve half the problem - you
can't get absolute position information, but you can zero the velocity
error.
-Sean
On 12/02/2011 5:50 PM, Alan James wrote:
Thanks Sean,
So if the mother ship isn't anchored & is
flowing in a current the unit won't pick this up, as the submarine
upon
launching won't
be accelerating.
If the mother ship was anchored in a
current the unit would need turning on prior to the sub being
released into the current to pick up that movement.
There was an additional unit with gyro for
$100- US
Regards Alan