(12) United States Patent
`Scherzinger
`
`USOO6853909B2
`(10) Patent No.:
`US 6,853,909 B2
`(45) Date of Patent:
`Feb. 8, 2005
`
`(54) WALKING STICK NAVIGATOR FOR
`POSITION DETERMINATION
`
`(75) Inventor: Bruno Scherzinger, Richmond Hills
`(CA)
`(73) Assignee: Applanix Corporation, INC,
`Richmond Hill, Ontario (CA)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 10/307,129
`(22) Filed:
`Nov. 29, 2002
`(65)
`Prior Publication Data
`US 2003/0114984 A1 Jun. 19, 2003
`Related U.S. Application Data
`(60) Provisional application No. 60/337,256, filed on Dec. 3,
`2001.
`(51) Int. Cl." ................................................ GO1C 21/00
`(52) U.S. Cl. ....................... 701/207; 701/213; 701/216;
`342/357.14
`(58) Field of Search ................................. 701/207,213,
`701/216, 220; 342/357.06,357.14; 702/5,
`160
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,512.905 A * 4/1996 Nichols et al. ........ 342/357.06
`5,583,776 A 12/1996 Levi
`5,734,348 A * 3/1998 Aoki et al. ............ 342/357.17
`5,956,660 A 9/1999 Neumann
`5,973,618 A * 10/1999 Ellis ........................... 340/990
`6,132,391. A 10/2000 Onari
`6,366.855 B1
`4/2002 Reilly
`6,401,036 B1
`6/2002 Geier et al.
`2002/0038178 A1
`3/2002 Talkenberg
`2002/009 1482 A1
`7/2002 Eakle, Jr.
`2002/0111717 A1
`8/2002 Scherzinger
`OTHER PUBLICATIONS
`Scherzinger, B. M. ; "Inertial Navigator Error Models For
`Large Heading Uncertainty”; IEEE Position Location and
`Navigation Symposium, 2001, pp. 2254-2263; abs.
`
`HeunSoo, L., Mase, K, Adachi, T., Oosawa, T., Nakano, K.,
`Sengoku, M; Hidaka, H.; Shinagawa, N.; Kobayashi, T,
`“Pedestrian Tracking Using GPS, Pedometer And Magnetic
`Compass”; Inst Electron Inf & Commun Eng., vol. 84 B No.
`12; Dec. 2001;pp. 2254-2263; abs.
`Brbaker, K. M.; “Soldier Systems Fusion”, Proceedings of
`the SPIE the International Society of Optical Engineering;
`vol. 3394; 1998; pp. 73–78; abstract.
`The Estimation and Control of Terrestrial Inertial Naviga
`tion System Errors Due to Vertical Deflections; Nash, IEEE
`Transactions on Automatic Control, vol. AC-13, No. 4,
`B/1968.
`Quentin Ladetto; On Foot Continuous Step Calibration
`Using Both Complimentary Recursive Prediction and Adap
`tive Kalman Filtering; Ion GPS 2000 Sep. 19–22, 2000 Salt
`Lake City, UT; pp. 1735–1740.
`
`* cited by examiner
`
`Primary Examiner Michael J. Zanelli
`(74) Attorney, Agent, or Firm-James F. Kirk
`(57)
`ABSTRACT
`A walking Stick navigator (WSN) apparatus and method
`comprises an aided INS (AINS) on a staff assembly with the
`“look and feel” of a GPS survey instrument. When GPS is
`available, the AINS is aided by GPS data, and the Survey or
`manipulates the staff assembly like a standard GPS survey
`instrument. When GPS is not available due to signal
`obstruction, the Surveyor manipulates the Staff assembly as
`a walking Stick. A Switch means coupled to the lower end of
`the Staff assembly provides a Stationary interval Signal when
`the Surveyor plants and holds the WSN on the ground while
`walking. A digital computer is coupled to be responsive to
`AINS output signals and to the Stationary interval Signals
`and to run a program that Solves a position aiding algorithm
`and a Velocity aiding algorithm that provide at least one
`aiding input to the AINS for each Successive Stationary
`interval.
`
`24 Claims, 13 Drawing Sheets
`
`
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`US. Patent
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`2B909,
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`Sheet 2 of 13
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`US 6,853,909 B2
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`
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`48
`
`FIG 2
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`Sheet 3 of 13
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`US 6,853,909 B2
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`
`
`80
`
`T
`
`24 f(zíž
`s312.
`(2)-2-7e 33.
`
`3.
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`U.S. Patent
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`Sheet 4 of 13
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`US 6,853,909 B2
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`
`
`FIG 4
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`Sheet 5 of 13
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`US 6,853,909 B2
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`
`
`66
`IGRLA
`VECTOR
`O6
`--
`FIG, 5
`
`58
`-)
`
`--
`
`.
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`U.S. Patent
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`Sheet 7 of 13
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`Sheet 8 of 13
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`US 6,853,909 B2
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`Tk.
`--
`
`T
`Tk-
`— — —
`". .
`.
`f
`f2
`Integration interval t to t2 is processed at the next
`Kalman filter measurement update at T.
`FIG. 8a
`
`Tk-l
`
`T
`
`---
`}
`\
`
`t 2
`
`Y
`
`/
`
`w
`
`N
`
`T kill
`A
`
`|
`f
`
`M
`
`Integration interval t to
`T, is processed at the next
`Kalman filter measurement
`update at Tk.
`FIG 8b
`
`Integration interval T to
`t 2 is processed at the next
`Kalman filter measurement
`update at T: , i.
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`Sheet 9 of 13
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`US 6,853,909 B2
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`- '
`
`t
`
`'
`
`'
`
`
`
`' and
`
`Tic marks represent
`Kalman filter cycles
`
`12
`
`70
`
`20
`
`-
`
`22
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`Sheet 10 0f 13
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`US 6,853,909 B2
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`36
`
`GPS
`
`- 24
`
`IMU
`
`94
`
`GROUND
`SWITCH
`
`-
`u- 130
`
`
`
`ANS
`PROCESSOR
`
`FIG.
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`Sheet 11 of 13
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`US 6,853,909 B2
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`to
`
`132
`
`-
`
`Yes
`
`Was
`the Ground Switch
`previously On?
`
`36
`
`Was
`the Ground switch
`previously On?
`
`
`
`
`
`
`
`Update SNV
`interated velocity
`- Air SNV 1-2
`Equation 7)
`
`Start SNV velocity
`integration
`- il
`AP SNY 12
`(Equation 7)
`
`
`
`
`
`
`
`Compute relative IMU
`position vector
`f2
`(Equation 5)
`and relative IMU
`displacement
`- A?2
`(equation 6)
`
`- 46
`
`
`
`Compute relative
`IMU position vectol
`
`(E ution 4)
`
`
`
`
`
`
`
`
`
`Compute
`position increment
`In easurement
`(equation 8, 9)
`
`FIG 2
`
`Send the
`measurement to the
`aided INS algorithm
`(Figure )
`y
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`Sheet 12 of 13
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`US 6,853,909 B2
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`150
`
`
`
`YES
`
`Is
`the Ground Switch
`On?
`
`
`
`Compute relative
`IMU velocity
`(Equation 10)
`
`
`
`
`
`
`
`
`
`
`
`Construct ZPUD
`Inca Sulrelinent
`(Equation ll, 12)
`
`
`
`Send the
`measurement to the
`aided INS agorithm
`(Figure 1)
`
`158
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`Sheet 13 of 13
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`US 6,853,909 B2
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`60
`
`Enter
`
`IS
`WSN measurement
`available
`
`u- 170
`Run Kalman filter
`With WSN
`ImeaSurellent
`(Figure 1)
`
`72
`
`
`
`Correct inertial
`navigator with
`estimated errors
`(Figure )
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`IS
`IMU data
`available
`')
`
`Run incrtial
`navigation
`algorithm
`(Figure I)
`
`Run WSN
`neaSuleinent
`algorithm
`(Figure 9 or 10)
`
`
`
`
`
`
`
`
`
`
`
`
`
`FIG.
`
`14
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`1
`WALKING STICK NAVIGATOR FOR
`POSITION DETERMINATION
`
`US 6,853,909 B2
`
`5
`
`15
`
`25
`
`This application claims priority from U.S. provisional
`patent application No. 60/337,256 filed Dec. 3, 2001 for “A
`WALKING STICK NAVIGATOR FOR POSITION
`DETERMINATION BACKGROUND OF THE INVEN
`TION” and having a common inventor and assignee.
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The subject invention is an Aided Inertial Navigation
`System (AINS) configured for land Survey applications and
`having the form and function of a standard GPS survey
`instrument. The invention uses an AINS as a navigational
`reference, which makes it possible to Survey areas where
`GPS Signals may be missing for time intervals of varying
`duration, or indefinitely, due to building obstruction, opera
`tion inside a building, tree foliage and or a dense tree
`canopy. An AINS that is normally aided with a radio
`positioning System Such as GPS but loses position aiding as
`a result of Signal blockage enters into a dead reckoning
`navigation mode, and requires Some alternative form of
`aiding to control the position error drift. A typical Source of
`velocity aiding is a Zero velocity update in which the AINS
`is held Stationary periodically to reset the accumulated
`Velocity error to Zero. The Subject invention implements an
`AINS in a format that is similar to a standard GPS Survey
`instrument, and uses a novel method of Zero Velocity aiding
`to navigate through GPS outages caused by Signal blockage.
`2. Background of the Invention
`The Trimble 4700 Site Surveyor is an example of a GPS
`land Survey instrument that is Similar to the present inven
`tion. Similar products are available from other GPS manu
`facturers. The 4700 Site Surveyor has a staff with a GPS
`35
`antenna at the top end and a simple Spike at the bottom end.
`A hand-held control and display unit (CDU) can be alter
`natively held by the Surveyor or mounted to the staff at the
`approximate midpoint. Modern GPS receivers for Surveying
`are Small enough to be mounted to the Staff as well.
`Alternatively the receiver can be carried with the batteries
`that power the unit in a backpack carried by the Surveyor.
`The Surveyor walks to each point to be Surveyed, places the
`Spike at the bottom end on the point, and either records a
`position computed by the receiver or “occupies” the point
`for a period of time during which the receiver records data
`for post-Survey processing.
`The disclosed WSN is designed to have a “look and feel'
`similar to a typical GPS Survey instrument. It is believed that
`the WSN will gain acceptance among Surveyors fairly
`quickly because of its similarity to industry accepted GPS
`Survey instruments. The only additional field procedure that
`a Surveyor must conduct is to manipulate the WSN like a
`walking stick when GPS drops out.
`In operation, the Surveyor uses the WSN for dead reck
`oning navigation when GPS Signals become obstructed, as
`might occur inside or between buildings or in a forested
`area. The Surveyor walks a Survey trajectory and uses the
`WSN as a positioning System to Survey positions along the
`trajectory. Such Survey trajectories. Sometimes pass through
`areas where no GPS signals are available. The WSN must
`therefore navigate in a dead-reckoning mode with as little
`position drift as possible.
`SUMMARY OF THE INVENTION
`The WSN apparatus and process, programs and algo
`rithms described herein comprises and are employed in
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`connection with a Staff assembly 48, Such as a Standard
`Survey staff, and an AINS coupled to and aligned on the staff
`assembly 48 as is shown in FIG. 2. A GPS antenna is
`mounted at the top of the staff assembly 48 and an inertial
`measurement unit (IMU) assembly is mounted to the bottom
`of the staff assembly 48. A ground spike is mounted to the
`bottom of the IMU assembly. A Zero velocity UPDate
`(ZUPD) switch is coupled to the ground spike at the lower
`end of the Staff assembly and is arranged to transfer when the
`ground Spike touches the ground. A plunger is arranged to
`force or compress the ZUPD switch slightly as the ground
`Spike contacts the ground.
`Asurveyor manipulates the WSN, as in FIG. 5, when GPS
`signals are unobstructed and valid data from the GPS
`receiver is available. This method is the same as the method
`used with a standard GPS Survey instrument. The Surveyor
`manipulates the WSN as shown in FIG. 6 when GPS signals
`are obstructed and valid GPS data is not available. This
`procedure is referred to as “walking Stick manipulation'. AS
`the Surveyor moves along a path to be Surveyed, the Sur
`veyor positions the lower end of the WSN shaft assembly at
`a Stationary point. The Surveyor pivots the shaft around the
`Stationary point Substantially in the direction of Surveyor
`movement. At the end of the step or stride, the Surveyor lifts
`the shaft assembly and repositions the lower end of the shaft
`assembly at a Subsequent Stationary point beyond the Sur
`veyors advancing foot and in the direction of Surveyor
`movement. At the conclusion of a Stride, the Sequence is
`repeated.
`When the Surveyor positions the WSN shaft assembly, the
`ZUPDSwitch closes, which closure indicates that the ground
`Spike at the point of contact with the ground is Stationary.
`The WSN has a digital computer running a program Solving
`a position aiding algorithm, the digital computer being
`coupled to be responsive to AINS output Signals, Such as
`present position, for the calculation of IMU relative position
`vectors using Equations 4 and 5 below. The program Solving
`the position aiding algorithm also integrates the inertial
`navigator Velocity, using Equation 7 as shown later, to
`provide the inertial navigation displacement. The Stationary
`interval signals provided by the ZUPDSwitch closure define
`the time intervals during which the ground Spike is Station
`ary. The program Solving the position aiding algorithm uses
`Equations Such as (9) or (10) to provide at least one aiding
`input to the AINS for each successive stationary interval.
`The AINS processes the aiding data from the ZUPD Switch
`during a Stationary interval and thereby regulates the Veloc
`ity error and the position error growth during the time
`interval that GPS data is unavailable.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram of an aided INS system;
`FIG. 2 is a schematic side view of a WSN (walking stick
`navigator) configuration using a single GPS,
`FIG. 3 is a schematic sectional view of the IMU enclo
`Sure,
`FIG. 4 is a schematic side view of a WSN (walking stick
`navigator) configuration using two GPS receivers;
`FIG. 5 is a Schematic side view of the WSN held in its
`normal vertical position by a Surveyor,
`FIG. 6 is a Schematic Side view showing the geometry of
`a step during walking Stick manipulation;
`FIG. 7 is a Schematic side view of a WSN with two GPS
`receivers and antennas being manipulated by a Surveyor
`when GPS signals are available;
`
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`
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`
`35
`
`40
`
`3
`FIG. 8a is a graph showing the occurrence of a position
`increment interval tit occurring between Kalman filter
`measurement updates,
`FIG. 8b is a graph showing the occurrence of a position
`increment interval tit occurring over an interval extend
`ing from a point in a first Kalman filter interval to a point in
`time within a Successive Kalman filter interval;
`FIG. 9 is a graph showing the occurrence of a ZUPD
`interval tit that extends over a period containing six
`Kalman filter intervals;
`FIG. 10 is a schematic drawing showing a WSN with a
`backpack;
`FIG. 11 is a schematic drawing of a WSN functional block
`diagram;
`FIG. 12 is a flow chart for a position increment measure
`ment algorithm;
`FIG. 13 is a flow chart for a ZUPD measurement algo
`rithm;
`FIG. 14 is a flow chart for a WSN processing algorithm.
`DETAILED DESCRIPTION OF THE
`INVENTION
`Aided Inertial Navigation System
`FIG. 1 is a block diagram that shows the architecture of
`a generic AINS within phantom block 20. The AINS is
`provided with an initial present position input from a key
`board or other input device (not shown) on mode control bus
`25. The AINS comprises an Inertial Navigation System
`(INS) shown within phantom block 22 as having an inertial
`measuring unit (IMU) 24 and an inertial navigator 26. A
`Kalman filter 28 and an error controller 32 estimate INS
`errors and correct the INS 22 using inputs to the Kalman
`filter from one or more aiding sensors within block 34, such
`as a GPS antenna and receiver 36, a Doppler Radar 38, or a
`distance measuring instrument (DMI) 42. The Kalman filter
`28 and the error controller 32 process and provide correc
`tions for the inertial navigator 26 which periodically outputs
`a Sequence of corrected or blended present position Solutions
`in real time on output bus 27.
`The inertial navigator 26 is typically mechanized using a
`digital computer and navigational Software for processing
`signals from the IMU 24. The IMU comprises a triad of
`accelerometers (not shown) that measure total acceleration,
`and a triad of gyros (not shown) that measure total angular
`rate. The IMU 24 also provides process and interface
`electronics (also not shown) that convert and output inertial
`acceleration and angular rate Signals in a digital format. The
`inertial navigator System 22 mechanizes Newton's equations
`of motion using the aforementioned navigational Software
`and digital computer (not shown).
`The INS 22 initially performs a ground alignment after
`which it transforms signal data from its package or vehicle
`navigation coordinate frame into a fixed and earth
`referenced coordinate System, Such as a north, east and down
`referenced System. A typical ground alignment or gyro
`compassing alignment requires the INS to be Stationary for
`5-15 minutes. The INS uses its accelerometers to establish
`the direction of the gravity vector. With the latitude of the
`INS present position as an input, the inertial navigator
`calculates the horizontal component of rotational rate that a
`horizontal north pointing referenced axis would experience.
`The alignment process then adjusts the body-to-earth direc
`tion cosine matrix (DCM) as required to match the measured
`roll rate of the transformed north pointing body axis to the
`calculated roll rate for the north pointing axis. Accelerom
`eter and gyro axis rates are thereafter transformed into earth
`referenced data using the adjusted DCM.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`In Some mechanizations, the horizontal north pointing
`axes is aligned to a heading other than north and east and the
`heading offset angle is called the wander angle.
`The IMU 24 generates incremental velocities and incre
`mental angles at the IMU sampling rate, typically 50 to 500
`Samples per Second. The corresponding IMU Sampling time
`interval is the inverse of the IMU sampling rate, typically /so
`to /500 Seconds. The incremental Velocities are obtained
`from outputs of the IMU accelerometers that are integrated
`over the IMU sampling time interval. The incremental
`angles are the angular rates from the IMU gyros integrated
`over the IMU sampling time interval. The inertial navigator
`26 receives the sampled inertial data from the IMU 24 and
`computes the current IMU present position (typically
`latitude, longitude, altitude), Velocity (typically north, east
`and down components) and orientation (roll, pitch and
`heading) at the IMU sampling rate. Mode control bus 25
`provides management and data Signals to the AINS from an
`external Source Such as a keyboard or a ground Switch.
`The aiding Sensors in block 34 represent any Sensors that
`provide navigation information that is Statistically indepen
`dent of the inertial navigation solution that the INS gener
`ates. Examples of aiding Sensors include one or more Global
`Navigation Satellite System (GNSS) receivers, an odometer
`or distance measuring indicator or instrument (DMI), and a
`Doppler radar providing velocity data. The U.S. Global
`Positioning System (GPS) and Russian GLONASS are the
`currently available GNSS systems, and GPS is the most
`widely used for navigation and Survey applications. The
`European Galileo System is Scheduled to become an avail
`able GNSS within the next 10 years. The embodiment of the
`invention described in the Subsequent text uses one or two
`GPS receivers. Future embodiments may use other GNSS
`receivers that may become available.
`The Kalman filter 28 is a recursive minimum-variance
`estimation algorithm that computes an estimate of a State
`vector based on constructed measurements. The measure
`ments typically comprise computed differences between the
`inertial navigation Solution elements and corresponding data
`elements from the aiding Sensors. For example, the com
`puted inertial-GPS position difference measurement com
`prises the differences between the respective latitudes and
`longitudes computed by the inertial navigator 26 and the
`latitudes and longitudes measured and reported by a GPS
`receiver. The true positions cancel in the differences, So that
`the differences in the position errorS remain. A Kalman filter
`designed for use with an INS and aiding sensors will
`typically estimate the errors in the INS and aiding Sensors.
`The INS errors typically comprise the following: INS posi
`tion errors, INS velocity errors, INS platform misalignment
`errors, accelerometer biases and gyro biases. Aiding Sensor
`errors can include the following: GPS north, east and down
`position errors, GPS carrier phase ambiguities and a DMI
`Scale factor error.
`The error controller 32 computes a vector of resets from
`the INS error estimates generated by the Kalman filter 28
`and applies these to the inertial navigator integration
`processes, thereby regulating the inertial navigator errors in
`a closed error control loop. The inertial navigator errors are
`thereby continuously regulated and hence maintained at
`Significantly Smaller magnitudes.
`The State-of-the-art in aided inertial navigation is mature.
`The technology originated in the late 1960's. An excellent
`example of a textbook on the Subject is “Aerospace Avionics
`Systems, A Modern Synthesis”, by George Siouris published
`by Academic Press in 1993.
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`S
`
`AINS Land Surveyor
`An AINS land Surveyor is any embodiment of an AINS
`carried by a Surveyor for the purpose of measuring position
`fixes. The AINS land Surveyor does not require access to the
`sky, as does a GPS receiver, and hence can be operated under
`a dense tree canopy, underground or inside buildings, Sce
`narios where a GPS receiver cannot function. An example of
`a high performance AINS land Surveyor is the Applanix POS
`LS. This is a backpack-borne instrument design for con
`ducting Seismic Surveys. It allows a Single Surveyor to walk
`and establish Surveyed positions among the trees in a forest
`without requiring trees to be cut to establish a Survey lane,
`as does a survey conducted with a GPS Survey instrument,
`a laser theodolite or a total Station. The cost Savings can be
`large, as the operation does not need to pay for "slasher'
`crews that cut the trees or the Stumpage fees for trees that are
`cut down and not always harvested. The environmental
`impact is also low to non-existent.
`A current embodiment of an AINS-based land Surveyor
`such as the POS LS require the surveyor to bring the AINS
`to a complete rest periodically, typically every 1–2 minutes,
`for a period of 15-30 seconds. This is called a zero-velocity
`update (ZUPD). The Kalman integration filter uses these
`Zero velocity observations to Zero the INS velocity error and
`partially calibrate inertial Sensor errors. The position error
`drift with periodic ZUPD's is on the order of 1-2 meters per
`kilometer. The requirement for ZUPD's is often an
`inconvenience, Since it limits the Surveyor's production.
`Possible methods by which a current AINS land Surveyor
`determines a Stationary condition include the following. The
`AINS detects and processes the ZUPD automatically using
`the INS velocity. In the alternative, the surveyor identifies a
`ZUPD by way of a signal to the INS from a switch.
`Automatic ZUPD detection can be unreliable because it
`must include tolerance for an INS velocity drift between
`ZUPD's, typically on the order of a few centimeters per
`Second. This admits false ZUPD detection when the Sur
`veyor has come to a stop for Some reason other than an
`intentional ZUPD. Having the Surveyor identify a zero
`Velocity condition admits Surveyor error. In either case, an
`incorrectly identified ZUPD processed by the AINS Kalman
`filter can cause the AINS Kalman filter to develop inaccurate
`INS error estimates and lead to a performance failure in the
`AINS land Surveyor.
`Precise Pedometer Navigator
`A PPN (Precise Pedometer Navigator) is disclosed in
`provisional U.S. Patent Application Ser. No. 60/266,481
`which was formalized in non-provisional U.S. patent appli
`cation Ser. No. 09/905,015 which was filed Jul. 13, 2001 for
`“A Pedometer Navigator System”. The “015” application
`issued as U.S. Pat. No. 6,594,617 B2 on Jul. 15, 2003. This
`application and its corresponding U.S. Patent have a com
`mon inventor and assignee. Non-provisional U.S. patent
`application Ser. No. 09/905,015 and U.S. Pat. No. 6,594,617
`B2 provide an alternative method to ZUPD's for an INS in
`a Pedometer Navigation System. The embodiment of the
`PPN taught in U.S. Pat. No. 6,594,617 B2 uses a short
`baseline position measurement subsystem SBPMS to mea
`Sure the relative positions of the Surveyor's feet with respect
`to the INS to establish the displacement of the INS with
`respect to a Stationary foot when either foot is Stationary. An
`example of an SBPMS is a magnetic position Sensor Such as
`the Fastrak product from Polhemus Incorporated
`(Colchester, Vt.). When the surveyor is walking, one foot
`will be stationary while the other is moving, and both feet
`will be Stationary during a step, provided that the Surveyor
`walks and doesn’t run or jump. This relative displacement
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`information becomes aiding information to the AINS algo
`rithm in the AINS land Surveyor in place of the aiding
`information that ZUPD's provide. Art relevant to this dis
`closure should teach the concept of referencing the INS
`position to a Stationary ground point that a precise pedom
`eter navigator identifies. The applicant has also filed an
`application for an AINS Land Surveyor System With Repro
`cessing having Ser. No. 60/252,862, filed on Nov. 22, 2000
`having a common assignee. A corresponding non
`provisional was filed on Nov. 14, 2001 having Ser. No.
`09/992,844.
`Notation
`The following notation is used in the description that
`follows: X denotes a vector with no specific reference frame
`of resolution.x denotes a vector resolved in a coordinate
`frame called the a-frame. All coordinate frames are right
`handed orthogonal frames. This implies that the X-Y-Z axes
`form an orthogonal triad in the forward, right and down
`directions. Typical coordinate frames of interest are the
`geographic frame (g-frame) whose principal axes coincide
`with the North, east and down directions, and the inertial
`Sensor body frame (b-frame), whose principal axes coincide
`with the input axes of the inertial Sensors.
`Subscripts on vectors are used to indicate a particular
`property or identification of the vector. For example, 1s'
`denotes the lever arm vector resolved in the a-frame from the
`inertial Sensor frame origin S to a GPS antenna phase center
`G.
`Matrices are designated with capital letters. C. denotes a
`direction cosine matrix (DCM) that transforms a vector from
`,
`ba
`the a-frame to the b-frame, i.e., x'=C X “.
`Time dependency of a quantity is indicated with round
`brackets around a time variable or index. For example,
`C(t) denotes the value of the DCM at time t.
`An increment of a variable is indicated with the symbol A.
`For example, A X denotes the increment of the vector X
`over a predefined time interval. An error in a variable is
`indicated with the symbol 8. For example, 8 x denotes the
`error in the vector X. ÖA X denotes the error in the incre
`ment of x over a predefined time interval.
`Look and Feel
`The WSN is designed to have a “look and feel” similar to
`that of a typical GPS Survey instrument. The Surveyor
`manipulates the WSN as he would manipulate a GPS survey
`instrument when adequate GPS Signal reception is available.
`This involves carrying the instrument from one point to be
`Surveyed to another, usually So that the instrument is vertical
`and the GPS antenna has access to the sky. When GPS signal
`Strength is unacceptable for Surveying, the Surveyor then
`manipulates the WSN like a walking stick.
`FIG. 2 shows the basic WSN configuration. The WSN
`computes the Surveyor's position on the earth from an AINS
`aided by GPS when the GPS signal strength is adequate and
`by ZUPD's during GPS outages. A survey staff assembly 48
`comprises an upper staff 50, an upper staff lock 52, a bubble
`level 56, a lower staff 54, and ground spike 58. FIG. 2 also
`depicts GPS antenna 60, handgrip 62, navigation computer
`system 64, IMU enclosure 66, control and display unit 70,
`data and power wire harness 72 and a power module 74. The
`Survey staff assembly 48 is a standard item that can be
`obtained from a Supplier of Survey equipment.
`The upper staff 50 telescopes into the lower staff 54 and
`is locked into position with the upper staff lock 52 for
`storage. The top of the upper staff 50 typically has a 5/8-inch
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`US 6,853,909 B2
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`coarse threaded stud to which a GPS antenna or retro
`reflector can be attached. The bottom of the lower staff 54
`also has a 5/8-inch coarse threaded Stud which is attached to
`top cap 78. Top cap 78 is attached to IMU enclosure 66 as
`shown in FIG. 3. IMU enclosure 66 is attached to bottom cap
`84, and ground spike 58 is attached to bottom cap 84. The
`Surveyor uses the bubble level 56 to move the Survey staff
`to a vertical orientation.
`The GPS antenna is mounted on the top end of the Survey
`staff 48. When the staff is held in its normal vertical position,
`the antenna faces the sky. The IMU enclosure 66 is mounted
`on the bottom end of the shaft, so that the IMU is close to
`the ground when the staff is held in its normal vertical
`position.
`The navigation computer system (NCS) 64 contains a
`GPS receiver and computer subsystem. The GPS receiver
`receives the radio frequency (RF) signal from the GPS
`antenna 60 and computes either observables for each tracked
`Satellite (pseudorange, carrier phase, ephemeris parameters)
`or a GPS navigation Solution (position in geodetic
`coordinates). The computer Subsystem performs all naviga
`tion data processing. The control and display unit (CDU) 70
`displays information from the WSN for the Surveyor to view
`and receives control signals from the Surveyor to the WSN.
`The power module 74 contains batteries and power man
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`agement electronics for powering the WSN. The data and
`power wire harness 72 provides the electrical interface
`between the CDU 70, power module 74 and NCS 64. In the
`preferred embodiment, the surveyor carries the CDU 70 and
`power module 74 in a backpack or on a specially designed
`belt. In alternative embodiments, these components can be
`mounted on the survey staff.
`FIG. 3 shows a preferred embodiment of the IMU enclo
`sure 66 mounted to the bottom end of the Survey staff
`assembly 48. The following components are shown in FIG.
`3: top cap 78, enclosure cylinder 80, IMU mounting plate
`82, and bottom cap 84. The top cap 78 is machined so that
`the bottom end of the Survey staff assembly 48 (the lower
`staff 54) screws into a 5/8-inch coarse threaded center hole.
`The conical shape of the top cap 78 provides a rigid interface
`between the Survey staff and the IMU enclosure 66. The
`IMU 86 is mounted to the IMU mounting plate 82 position
`ing the IMU 86 inside of the enclosure cylinder 80. The top
`cap 78 is fastened to the enclosure cylinder using Screws in
`threaded holes, by bonding, welding, or by the threaded
`engagement of the two parts. The IMU mounting plate 82
`can be fastened to the enclosure cylinder 80 and the bottom
`cap 84 to the IMU mounting plate 82 in a likewise manner.
`The bottom cap 84 contains the ZUPD Switch assembly
`90. The ZUPD switch assembly 90 has a shock isolator 92,
`a ZUPD Switch 94, a plunger spring 96, a plunger 98 and
`ground spike 58.
`The ground spike 58 is a standard component of the
`Survey staff. The plunger 98 has a 5/8-inch coarse threaded
`stud to which the ground spike 58 is screwed. The plunger
`98 is the interface between the ground spike 58 and the
`ZUPDSwitch94. The plunger spring 96 exerts a force on the
`plunger 98 that pushes the plunger to its normally extended
`position. The plunger Spring 96 can be a coil Spring, leaf
`Spring or compressible material Such as rubber. AS the
`Surveyor plants the ground spike of the WSN into the earth,
`the ground spike 58 supports the weight of the WSN. The
`upward force applied by the ground Spike compresses the
`plunger Spring and drives the plunger 98 into a compressed
`State. The plunger Spring 96 is an optional component that is
`not required if the ZUPD switch 94 provides its own return
`or restoring force.
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`The ZUPDSwitch 94 can be an