Walking stick navigator for position determination

A walking stick navigator (WSN) formed on a staff assembly having a lower end terminating in a spike, and a top end, a surveyor supporting the staff assembly while walking, the surveyor positions the staff assembly lower end to be in contact with the ground at a fixed point in front of the surveyor at the beginning of a step marking the start of a stationary interval, the surveyor pivoting the staff assembly about the fixed point in the direction of his movement, and raising the staff assembly to interrupt the shaft lower end contact with the ground at the fixed point at the conclusion of each step marking the end of the stationary interval, the WSN comprising:

• an AINS having an IMU providing output signals developed at least partially from the outputs of a plurality of inertial sensors,
• a position measurement process responsive to the AINS output signals for providing a position increment measurement vector to the AINS during a portion of each step for each respective stationary interval to control position error drift.

12 The WSN of claim 11 further comprising:

• a switch means for providing a stationary interval signal to the AINS characterizing the interval during which the shaft lower end is in contact with the ground.

The WSN of claim 12 wherein the AINS further comprises a Kalman filter designed be responsive to the position increment measurement vector {right arrow over (z)}SNV-PP for each stationary period for estimating and regulating position and velocity vector errors to obtain a low position error drift.

The WSN of claim 20 wherein the position measurement process further comprises:

• an algorithm for calculating a position increment measurement by calculating a first relative IMU displacement at the beginning of the contact signal and a second relative IMU displacement at the conclusion of the contact signal and calculating a time synchronised relative IMU displacement vector from the difference between the second relative IMU displacement and the first relative IMU displacement vectors, the algorithm obtaining the inertial navigation solution for the contact signal interval from the inertial navigation system and calculating a position increment measurement from the difference between the inertial navigation solution and the time synchronised relative IMU displacement.

The WSN of claim 20 wherein the position measurement process further comprises:

• an algorithm for calculating a ZUPD measurement having an IGRLA vector input defining the location of an IMU on the shaft assembly with respect to the lower end of the shaft assembly, the algorithm calculating a the relative IMU velocity with respect to stationary ground at each Kalman filter cycle time from the beginning of the contact signal until the end of the contact signal by taking the cross product of the angular rate of the IMU with the IGRLA vector while in contact with the ground, and multiplying each respective cross product by the direction cosine matrix for a body to navigational reference system, the process then constructing the ZPUD measurement by subtracting the relative IMU velocity from the equivalent inertial velocity.

The WSN of claim 20 further comprising:

• a GPS receiver providing acceptable GPS position aiding signals to the AINS, the surveyor moving along a path to be surveyed, the surveyor carrying the staff assembly with the lower end above the ground during intervals in which acceptable GPS position aiding signal to the AINS are available, the staff assembly having the look and feel of a GPS survey instrument during intervals in which acceptable GPS position aiding signals are being transferred to the AINS.

The WSN of claim 20 further comprising:

• a GPS receiver providing acceptable GPS position aiding signals to the AINS, the surveyor moving along a path to be surveyed, the surveyor carrying the staff assembly lower end above the ground during intervals in which an acceptable GPS position aiding signal to the AINS is available, the surveyor manipulating the staff assembly like a standard GPS survey instrument, the staff assembly being characterised as having the “look and feel” of a GPS survey instrument during intervals in which acceptable GPS position aiding signals are being transferred to the AINS.

The WSN of claim 20 further comprising a GPS receiver coupled to provide a GPS aiding signal to the AINS as the surveyor moves along a path to be surveyed, the surveyor carrying the staff without contact with the ground during intervals when an acceptable GPS signal are available, the AINS being aided by GPS data, the surveyor manipulating the staff assembly like a standard GPS survey instrument during intervals in which an acceptable GPS receiver is available, and when GPS is not available, due to signal obstruction, the surveyor manipulating the staff assembly as a walking stick while the surveyor is walking, the surveyor bringing the lower end of the shaft assembly into contact with the ground, the switch providing the contact signal, the input process being responsive to the contact signal and coupled to the AINS output signals to provide at least one aiding input signal to the AINS for each successive stationary interval.