Evaluation of Geometry Data Error Performance on A  Geometry Car Using
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Evaluation of Geometry Data Error Performance on A Geometry Car Using Geometry Data Alignment Techniques. H. James Rome Rome Navigation Innovations,Inc 27 Old County Rd, Gloucester , MA 978-281-5623 [email protected]

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Show by example how evaluation of data performance in general will be carried out

Evaluation of Geometry Data Error Performance on A Geometry Car Using Geometry Data Alignment Techniques

H. James Rome

Rome Navigation Innovations,Inc

27 Old County Rd, Gloucester , MA

978-281-5623

[email protected]

  • Show By Example How Evaluation of Data Performance in General Will Be Carried out

  • Showcase Geometry Data Alignment Techniques as A Solution to Many Problems.

Purpose of the Presentation


Presentation concentrates on a case study comparison of alternate and standard gage

Presentation Concentrates on a case Study: Comparison of “Alternate” and Standard Gage

  • Example of Performance Analysis

  • Investigate Repeatability and stability of two measures of gage.


What s this geometry data alignment package

What’s This Geometry Data Alignment Package?

  • Lines up data from several runs to data on Reference Run. Can align data to an Accuracy ~ 1 ft

  • Used For:

    • Trend Analysis

    • Repeatability and Error Analysis

  • Example Follows


Show by example how evaluation of data performance in general will be carried out

Example …Before Data Alignment:

Plot .vs.time at ft location37825

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Profile, Inch,->

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time back from reference run, months

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Left Profile Lined up with GPS to about

2 meters

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Show by example how evaluation of data performance in general will be carried out

Plots after Data Alignment up with With Package,

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Distance along track, ftX104 ->

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Plot .vs.time at ft location37825

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Trend Apparent

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Profile, Inch,->

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time back from reference run, months


Use of alignment for error analysis

Use of Alignment for Error Analysis

  • Approach can be used to Evaluate Repeatability Errors.

    • If Data is Taken Close Enough in time, Differences in Aligned Data imply the sum of the errors in Both measurements .. examples follow


Show by example how evaluation of data performance in general will be carried out

NOTE!

  • This alignment can be carried out over 10’s or even 100’s of miles with the click of a mouse.

  • Thus no need to constrain evaluations to a several thousand ft “Test Track”.

  • Occasional rare events, long term error error trends, and Data Reliability can be evaluated.


Example comparison of alternate and standard gage

Example Comparison of Alternate and Standard Gage

  • Both Measures were available on the Same Car

  • Two Runs over the same 70 mi of track were used for the Study

  • Each Is Analyzed as if the other did not exist

From an FRA Car ~ 2006


Snippet aligned alternate gage and standard gage

Snippet Aligned Alternate Gage, and Standard Gage

Alternate Gage

“Standard”

Gage

Is Noisier!

1000 Pt mean subracted

Standard Gage


Show by example how evaluation of data performance in general will be carried out

What We Do Next

X+1000

x

Take Difference of Two Curves

Find Root Mean Square of Difference,RMS

Plot RMS vs. X


Show by example how evaluation of data performance in general will be carried out

Plot of Running 1000 Pt. RMS differences

vs. Distance for Both Gages

plot of 1000 pt rms

alt gage differences

0.2

standard gage differences

0.18

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RMS (Units)

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Record # along track 

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RMS’s ~ 40 % Less for Alternate Gage


Note there is usually a calibration error in gage measurement

Note There is usually a Calibration Error in Gage Measurement

  • Is the Calibration Stable During the Run?


Show by example how evaluation of data performance in general will be carried out

Sample of

Gage Aligned with ( 1000 pt) Bias Removed the Bias

Gage, Inches

Distance along track,ft


Show by example how evaluation of data performance in general will be carried out

Sample of Gage Aligned gage

..NOTE here Bias is not removed!

Gage, Inches

Distance along track,ft

Is this “Bias” stable?


Show by example how evaluation of data performance in general will be carried out

Plot of 1000 pt Mean difference of same Paramter:

for Alternate and Standard Gages Vs. Distance

plot of 1000 pt mean vs distance

0.35

alt gage

standard gage

0.3

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Record # along track 

0.05

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x 10

Typical Max Shift…

Standard, .1” Alternative: .06”


Show by example how evaluation of data performance in general will be carried out

From Histogram of All Differences, Find

Cumulative Distribution

FRACTION ACTUAL DIFFERENCES LESS THAN X, mean subtrated

1

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alt gage

standard gage

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Error Limits, (Units) X

Alternative Gage: 70% of error<.05’’

Standard Gage: ~ 70% of errors <.08’’


Show by example how evaluation of data performance in general will be carried out

Histogram of 1000 pt RMS errors For Both Gages.

Most Likely

Value Standard

~.075

Noise Floor

Most Likely

Value Alternative

~.055

Noise Floor

hisotragm of 1000 pt. RMS differences, mean subtrated

0.35

alt gage

standard gage

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Fraction in Bin

Less than ½ # Outliers!

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Bin Value , Linear Units


Show by example how evaluation of data performance in general will be carried out

Power Spectra, vs Frquency from Both Gages

0.12

Standard

Gage

Alternative

Gage

0.1

0.2

Note error power is about Double

for Standard Gage

0.08

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Period ~39 units

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Lots of High Frequency

Noise.

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Frequency, 1/( Unit record) 

Frequency, 1/ (Unit Record) 


Conclusions comparing standard and alternative gages

Conclusions Comparing Standard and Alternative Gages

  • Alternative Gage has significantly:

    • Lower RMS errors

    • Fewer large Errors

    • More Bias Stability

    • Less high Frequency Noise

  • Bottom Line: From the Point of View of Repeatability,Alternative Gage is Just Better!


Show by example how evaluation of data performance in general will be carried out

NOTE!

  • Most of this Quality Information could not be obtained from a short stretch of Data

  • With Automated Data Alignment, No test track required. Track of Opportunity can be used

  • Simply Run over same ( say 20-50 mile) length of track twice within a few days or weeks.


Other uses

Other Uses

  • Compare Results of GRMS Vehicles without having them Coordinate their Runs..and over a long distance.

  • Compare Geometry measurement Equipment

  • Find Fraction of time when there are data outages


What about other parameters

What About Other Parameters

  • The Key is the the ability to Align Massive amounts of Geometry car Data. It puts an Entirely new spin on how extensive and how inexpensive Quality Evaluation can be!

  • Similar studies can be carried out on Any measurement taken on the Geometry car

  • And That includes GPS


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