I have been using dual RTK receivers for my tractor projects. This gives me reliable position, heading, and tilt at low rates (10 Hz). I recently began working with an INS (an Advanced Navigation Spatial Dual) and it's wonderful to get a full Pose from a single device at up to 1000 Hz. The problem I have is that an INS like this is expensive (~$12K) and total overkill for what I'm doing (driving on ground at 5.5 MPH).
Is there a way to achieve an adequate result using FOSS? The articles I find on Kalman filtering seem to always assume that the NavSatFix does not provide sufficiently accurate absolute position data. RTK, however, does provide sufficient accuracy and precision for my needs.
Note that while I do have radar ground speed available, my strong preference is to just use RTK receivers and a MEMS IMU. Let's say that I want specifications comparable to my Spatial Dual but the update rate doesn't need to be over 100 Hz.
Update: I found this paper which addresses the constraints of a (slow land-based non-holonomic) vehicle.