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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:
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