GIS and GPS for Railroad Environment

Rome Navigation Innovations Inc 27 Old County Rd. Gloucester, MA 01930 James_Rome@uml.edu H. James Rome, President 978-281-5623 GIS and GPS for Railroad Environment Presented by:Jim Rome May 15, 2007

Why is Track Navigation different from most any other Navigation • It is mostly ONE DIMENSIONAL, Linear referencing! • Curves are mild , linear accelerations are mild. • A Map (if we have one) tells us everything except where along the track we are. We simply have to pin down that ONE quantity.

Its Sooo.. Easy! • Compare the Issue an aircraft pilot in flying and landing virtually blind. • Track Navigation is like shooting fish in a Barrel • Don’t Shoot yourself in the Foot!

What Follows • Preliminaries • Principles of GPS ( very very short course) • Issues of Rail Navigation • Data Integration and Handling • For Navigation • Navigation with Measured Data • The Railroad Receiver

Definitions • Purpose of GIS and Navigation:Locate something so you can find it again • Accuracy Required :Good enough to complete your “Mission” • Methods of Navigation on the Rails : • Dark Ages.. Locate by visual clues • Until Recently Locate by ft from Milepost (Requirements are often driven by capability) • NOW GPS…Adds a whole new Dimension of the One Dimensional Problem

Comparing Apples to Prunes • Never Try to Land a plane where a train navigates • A Plane for the most part can go any direction at any time and hardly ever stops. A Train for the most part goes forward and backward and stops all the time. • GPS on a plane is generally available. On a train, only if we are lucky. • On a train we Independently can find distance along the ground traveled to great precision. Not so on a plane.

Accuracy Integrity Reliability • Accuracy: RMS error 95 % limit of error, etc. • Integrity: know when to trust! Know when readings are false! ( Can cost lots of money when you don’t) • Reliability what fraction of the time ( space) is it working?

Why Know the Principles of Operations of GPS • So you know where it won’t work and where it might Shoot you In the foot! • Know what complements GPS. • Know what you might do with GPS.. And What you can’t . That is, understand issues. • Next is a very brief summary.

Principles of GPS Operation sat. time sat. time DT sat. time DT DT sat. time DT DT Observed Time Observed Time Observed Time Observed DT Time R3 Differential Corrections R4 R2 R1 Antenna /Receiver Compute Position Sat Positions Other Parameters Vehicle Position

NAVIGATION SOLUTION IF WE HAD 4 TIME MEASUREMENTS T1, T2,T3,T4 AND FOUR UNKNOWNS: X,Y,Z, DT Can Find position, X,Y,Z RANGE TO VEHICLE T1= [(Xs1-X)2+(Ys1-Y)2+(ZS1-Z)2] 1/2 /c + DT+ n1 T2= [(Xs2-X)2+(Ys2-Y)2+(ZS2-Z)2] 1/2 /c + DT+ n2 T3= [(Xs3-X)2+(Ys3-Y)2+(ZS3-Z)2] 1/2 /c + DT+ n3 T4= [(Xs4-X)2+(Ys4-Y)2+(ZS4-Z)2] 1/2 /c + DT+ n4 Speed of Light Noise Synch Error X orbit Pos. sat #2 Transmission Delay Time

ADDITIONAL FEATURES IN NAVIGATION SOLUTION • THERE ARE USUALLY MORE MEASUREMENTS: • T5= [(Xs5-X)2+(Ys5-Y)2+(ZS5-Z)2] 1/2 /c + DT+ n5 • T6= [(Xs6-X)2+(Ys6-Y)2+(ZS6-Z)2] 1/2 /c + DT+ n6 • USED FOR SELF CHECK AND IMPROVING ACCURACY • Least Squares Estimation • Integrity and Exclusion One Solution Using 4 Sats. Outlier, Sat 6 Bad? 1,3,4,6 1,2,3,4 Least Squares Estimate: HDOP*RMS Range=Nav. Error 1,3,4,5 1,2,4,5 Integrity Region 1,2,3,5 2,3,4,5

ADDITIONAL FEATURES IN NAVIGATION SOLUTION Differential Corrections: T3= [(Xs3-Csx3 -X)2+(Ys3 -Csy3-Y)2+(ZS3 -Csz3-Z)2] 1/2 /c – EP3+ DT+ n3 Orbit Corrections Propagation Corrections Types of Differential Corrections: VBS satellite (OmniStar) ~3 ft (they say 1ft) (800/yr) NDGPS (Free.. If available) 3-6 ft WASS (Satellite, Free) 10 ft. (Omnistar) 1500 HP Satellite 5 INCHES! ( 1500/yr) But They only work when there is GPS!

Types of Receivers • Hand Held ( WASS enabled) accuracy ~ 30 ft (10 ft) <$300 • Computer Cards .. Right in your laptop Accuracy 30 ft-~ 2 ft .. With cycle matching and Good differential • Receivers with cycle matching… 2 ft with good differential… better for “local corrections” • Dual Frequency ( gets rid of Ionospheric errors) Receivers have cycle matching, with base station positioning to cm or mm. ( Overkill?) • Inertial Aiding… probably won’t benefit railroad users, but fast recovery from outage will.

Issues of GPS and Train Navigaton Track Beds Are Not Designed for GPS Visibility -Issues Blockage of Sats./Differential Multi-path Total Wipeout Error in Differential Heading Odometer Dead Reckoning is Important

So What does One Dimension Buy US? • Linear Referenced track Map .. It will fit on a memory stick • If only we had a perfect Odometer, we would only need GPS occasionally • If only we didn’t have to use Figure skates to play Hockey….? • Example Next that could probably reduce the unavailability of GPS by a factor of 3

Solution: Two Satellites and a Track Map This is a great Concept, Easily Implemented. But Don’t expect a GPS Manufacturer to offer one Soon Line of Track Surface of Constant Time Difference

Why is this so special? • If any satellites in view, they will be fore and aft, and above .. Where they would be most effective! • No Receiver Does this because nobody with clout asked!( That is it is a feature that could be burned into a receiver chip)

Data IntegrationKalman Filter Software • Kalman Filter software usually uses GPS and aiding data . Example:odometer , heading reference, and/ or inertial system • Provides smooth outputs between fresh GPS samples • Can Provide Position Solutions ( albeit with growing errors) during GPS outages. • Can slightly improve accuracy over just Raw GPS • Can Provide good heading information • Can Reject bad data (A Key Feature )

Kaman Filter Should Also Provide: • Distance Along track • Heading • Quality of Solution ( Combination of Quality of Raw data, Expected error, Number of rejections) • Used to Tie Down Distance , assess precision of solution • If not, they are selling you a Figure skate for Hockey!

Comments on Integration Components in Kalman Filtering • Aircraft Grade GPS Inertial System would provide >100 ft along track accuracy extrapolating 1 mile at 60 Mph with no GPS. • GPS/Odometer/ heading reference (Could be curvature from Geometry) filter would provide <12 ft along track accuracy extrapolating 1 mile at 60 Mph with no GPS. • Cheap and simple implemented in post time • Guess which is a lot cheaper?

$ $ $ $ $ $ $ $ But then You have the GPS/INERTIAL /ODOMETER • Should be as good as the Odometer and HR…If it is integrated properly… at 5X to 10X the cost. • Your Geometry measurement System may need Inertial Data for Stabilization of measurements.. So get it , but not Just for position improvement!

How to get the Most out of Your GPS • Make Sure Your Receiver is Navigating !!!!!!! • Know where the GPS antenna is with respect to sensors (then you can compensate)! • Have a Track Map at least as accurate as your GPS (Do you have to? No more than you have to have air conditioning in you car in Texas) • A Chain is only as strong as its weakest link • When you plan think of Location and Re-Location!

About Synchronization • SYNCHRONIZE Your Sensors to Odometer • Odometer is your interpolator • SYNCHRONIZE Your GPS to Odometer • Odometer Distance between GPS outputs should be consistent with GPS distance Difference • SYNCHRONIZEGPS to Sensors ( Redundant? Maybe) • If you travel at 50 ft/sec, and there is a synch error of .2 sec between GPS output and Sensor,You are off by 10 ft! • Timing or Synch Jitter is the worst.. Because you can’t compensate! • GPS Latency: GPS solution is before time of output. Good receivers will extrapolate to to output time.

Using Odometer as Strobe • Most Geometry Car data is strobed to the (ft) count of the odometer. Its is logical • GPS Data should be ( and is in many systems) Strobed in the same way. • Fresh GPS is detected at change. • Sampling error can be no more that a ft. • When it is done right, everything is time synched( even though we might not exactly what time it is) • And yes, you can have a Kalman filter “without time”

GPS Sampling Rates • When there is an odometer providing data every ft or less, there is no need for GPS outputs faster that 1/sec… Software can do any necessary interpolation. • Faster GPS sampling means less sophisticated Interpolation software. • BUT it won’t significantly improve accuracies.

L2,l2,H2 L3,l3,H3 L1,l1,H1 S2 S3 S1 What should be on a Track Map? Format? • Dependent Variables :LAT/Long (Elevation), AZIMUTH every ~15 –50 ft • Independent Variable: Distance Along track Si: Preferably Derived from a GPS input based Algorithm • LAT/Long derived from survey,fly maps, or GPS derived maps. • Beware of Datum shifts (Does Positioning During Mapping use same earth model as Navigating GPS?)!

Can Make A Track Map With Geometry Car GPS , Ancillary data and Optimal Smoothing

Some Uses Of Track Map • Convert Lat/Long to distance along Track and vise/versa. Lets High tech meet low tech • Provide heading for Lever arm correction, and Estimation. • Provide common Base for Communication, data collection Defect file/map X X 312 ft Cracked Tie

What data to Record on the Big Guys • Latitude , Longitude, {Elevation} Time • Distance along track ( odometer) • Heading change( if Curvature is not on Geometry) • Integrity Related: • Differential Quality , • Hdop ( measure of accuracy), • number of satellites in solution (good for in finding integrity)… • Better: Sat numbers in solution ( can be used In post processing for correction)

If Kalman Filter Output is Available on Geometry Car • Kalman filter output of LAT/Long/Heading {Distance along Track or correction to Odometer} • {Filter Integrity Measure} • Measure of Raw heading change • + All data on previous slide • To Recover from “Computer and software crashes” • To Apply Optimal smoothing for more accurate positioning , and making semblance of map

Data To Collect on “Low Tech Little Brothers” Having GPS • At fault, lat/long , milepost and ft. If available • Distance from fault to next good GPS reading. Could be “0” • Lat/long at this point • With track map this is now a redundant measurement

Odometer Error Sources and Suggested Accuracies • Scale factor stability(.002 in say 200000 ft) • Random ( show example) • Low or no (Reasonable) speed sensitivity • Event related: • Wheel skips ( best to have odometer on “free wheel”) • Low speed effects( with magnetic odometers…test it at very low speeds)

This odometer Error Would be O.K. 160 140 120 100 80 Odometer Error, ft. Random Error 60 Scale Factor, slope =.00018 40 20 0 -20 -40 -60 0E0 200000 400000 600000 Distance along track, ft

Odometer Sampling Rates • For Geometry car collection • One pulse/ft MINIMUM • 10 pulses or better/ft better

Resultant Capabilities of Railroad Specific Receiver • Fast or seamless acquisition or reacquisition of signal after short length outages. • Differential Corrections wherever there is a GPS signal ( alternate modes of receiving differential corrections) • Capability 1-D navigation when as few as two satellites are in view and a track map available. (Extension of 2-D navigation when only three satellites in view) (Don’t Hold Your Breath) • Output only when there is High integrity or warning when Integrity cannot be validated

Rome’s Version of A Railroad Specific Receiver • For signal acquisition,reacquisition and tracking in weak signal environments • Maximum Bandwidths of Receiver tracking loops consistent with the Railroad Operation accelerations ( Should be Adjustable at least by Manufacturer ) • Tracking loop aiding consistent with Odometer /heading reference inputs ( should be better and cheaper than MEMS aiding, but is not currently available) • Antenna with rate Gyro (Certainly not Standard)

Rome’s Version of A Railroad Specific Receiver (Cont.) • RAIM (Internal Integrity Monitoring) tuned to accuracies of Differential Systems • Software consistent with (1-D) navigation … factoring in track map into solutions (may be a long time coming) • Built in integrity based on track maps • Receptors of Differential Corrections coming from “Broadband ( like internet, cell phone, even perhaps TV, track based communications… It will come!)

GIS and GPS for Railroad Environment