Sorry that I haven't responded sooner as we have had a power outage for most of the day on the facility where I reside.
Not familiar with the Microstrain 3DM-GX1. It appears that it is a 3-degree of freedom unit and for proper navigation 6-degrees of freedom are required…3 gyros (with low drift) and 3 accelerometers. You can review the IMU 6-DOF v2 unit at www.sparkfun.com that I briefly glanced over. They do not provide drift information and this is critical for determining the accuracy of your dead-reckoning. If the drift of this unit isn’t bad, it still has to be integrated into a nav package and the mathematics aren’t inconsequential…major matrix manipulation.
I believe that there are sonar units that will provide SOG information but haven’t looked into the matter for some time.
Jay K. Jeffries
Jay - how do the specifications of the $300 sensor you were looking at
compare to the Microstrain 3DM-GX1? Also, can an off-the-shelf sonar be
used to provide speed-over-ground?