Best-Fit, Bundle, & USMN Using SA to understand measurement uncertainty Zach Rogers NRK, EMEAR Application Engineer

TheBasics Getting Located in SA Best Fit Perform a best fit operation to locate an instrument to a set of reference points Identify how to use maximum error and RMS error to analyze the quality of a point-based fit Quick Align Perform an alignment direct to Part Surface using n-point alignments Identify “ good ” surface alignment schemes Frame Alignment Identify and measure alignment features to define the Part or Assembly coordinate system 3-2-1, Frame Wizard, 3-Plane and Frame to Frame Alignments Instrument Stations Explain instrument stations and the process of relocating an instrument. Identify several high-level methods for locating or relocating an instrument Getting Located in SA

BeyondTheBasics Getting Located in SA Bundle Combine multiple instrument stations with Combined Observations via a Bundle Adjustment Procedure USMN The Ultimate way to combine multiple instrument stations. Combine measurements using the instrument’s properties Calculate combined point uncertainties Understand how measurement setup affects measurement uncertainty Getting Located in SA Best Fit Perform a best fit operation to locate an instrument to a set of reference points Identify how to use maximum error and RMS error to analyze the quality of a point-based fit 01

BeyondTheBasics The Problems with Best Fit Getting Located in SA 3 01

BeyondTheBasics The Problems with Best Fit Getting Located in SA 4 Best Fit does not intelligently consider points. Less accurate 01

It is limited to one moving and one fixed set of points. BeyondTheBasics The Problems with Best Fit Getting Located in SA 5 01

Getting Located in SA 6 Leapfrogging leads to rapid error stack-up. True location True location Fit location Fit location A B C 01 BeyondTheBasics The Problems with Best Fit

A H B D E F G C Getting Located in SA 7 Measurement loops can’t be “ closed ”. 01 BeyondTheBasics The Problems with Best Fit

Provides no measurement uncertainty information Getting Located in SA 8 01 BeyondTheBasics The Problems with Best Fit

Getting Located in SA 9 Doesn’t yield a “ best set ” of measurements. Inst. 1 Inst. 2 Most Likely Point? 01 BeyondTheBasics The Problems with Best Fit

Bundle is a simultaneous solution! In contrast to best fits, Bundle can simultaneously optimize multiple instrument stations In this way, it is a better option then Best Fit! BeyondTheBasics Bundling Getting Located in SA 10 05

Bundle has special features! Scale Bars, Mirror Cubes, and Collimation shots are all understood by SA’s Bundle Scale Bars can be weighted based upon their calibrated length uncertainty values Instruments can be “ forced ” vertical BeyondTheBasics Bundling Getting Located in SA 11 05

*Bundle requires targets with Multiple Observations! When Best Fitting, you will have one Point Group per station. The Point Names in each group will be matched up For Bundle, all instruments must measure the same Point. GroupNames & PointNames will be identical for all instruments In this way, each point will have multiple observations BeyondTheBasics Bundling Getting Located in SA 12 05

BeyondTheBasics Bundling Getting Located in SA BunldleBest-Fit

BeyondTheBasics Bundling Getting Located in SA Bundle Process 1. Measure instrument locator features (points, scalebars, mirror cubes, collimation, etc) 2. Instrument  Bundle Adjust 3. Select instrument(s) to add to Bundle (note:usually, all EXCEPT for one instrument) 4. Adjust option(s) if desired & Begin Computation After accepting results, selected instrument(s) position will be updated in SA

Demo 1 Instrument  Bundle Adjust … Bundle Example.xit64 Performing a bundle adjustment in SA Getting Located in SA 15 05

Bundle is best fit, performed in Angular Values For instruments that only measure angles, this is great! When distance measurements are involved, any deviation in distance measurements are converted to angles at the measured distance All measurements are then given equal weighting, in angular space BeyondTheBasics Bundling Getting Located in SA 16 05

BeyondTheBasics Bundling Getting Located in SA 17 05

It uses constant weighting BeyondTheBasics The Problems with Bundling Getting Located in SA 18 05

Provides no measurement uncertainty information BeyondTheBasics The Problems with Bundling Getting Located in SA 19 05

Getting Located in SA 20 Without uncertainty, Bundle can not provide a true “ best set ” of measurements. Inst. 1 Inst. 2 Most Likely Point? 01 BeyondTheBasics The Problems with Best Fit

Questions on Bundling? We have answers! Getting Located in SA 21

BeyondTheBasics USMN Getting Located in SA USMN The Ultimate way to combine multiple instrument stations. 06

1.Solves multi-station networks simultaneously. 2.Uses measurement information intelligently. 3.Yields ideal network of common points. 4.Provides uncertainty information for all measurements. 5.Can be used to characterize measurement system performance. 6.Provides results both numerically and graphically. BeyondTheBasics USMN Getting Located in SA The Advantages of USMN

BeyondTheBasics USMN Getting Located in SA BunldleBest-Fit USMN

BeyondTheBasics USMN Getting Located in SA USMN Process 1. Measure common points 2. Analysis  Coordinate Uncertainty  Unified Spatial Metrology Network 3. Select instruments to include in USMN solutions (note:usually all instruments) 4. Use “ Best-Fit Then Solve ”, or “ Auto Solve ” 5. Evaluate results and trim outliers as desired. After accepting results, selected instrument(s) position will adjusted in SA, relative to the instrument left as “ fixed ” in the USMN dialog

BeyondTheBasics USMN Getting Located in SA Max Errror (3) Statistical (relative) Ranking (2) Auto Solve (1) Pt Uncertainty Analysis (4) Apply (5)

BeyondTheBasics USMN Getting Located in SA Fixed Instrument (unchecked) Moving Instrument (checked) Best-Fit then Solve Include/Exclude Pts

Demo 2 USMN; Analysis  Coordinate Uncertainty  Unified Spatial Metrology Network USMN1.xit64 Performing a 2 Station USMN solution, and creating a USMN Composite output group Getting Located in SA 28 02

1.Solves multi-station networks simultaneously. 2.Uses measurement information intelligently. 3.Yields ideal network of common points. 4.Provides uncertainty information for all measurements. 5.Can be used to characterize measurement system performance. 6.Provides results both numerically and graphically. 4.Provides uncertainty information for all measurements. BeyondTheBasics The Problems with Bundling Getting Located in SA The Advantages of USMN

Uncertainty of Measurement VIM 3.9 (taken from ISO GUM) Parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand. BeyondTheBasics USMN Getting Located in SA Uncertainty

“ A measurement result is complete only when accompanied by a quantitative statement of its uncertainty. ” -National Institute of Standards and Technology (NIST) BeyondTheBasics USMN Getting Located in SA 31 06

“ When reporting the result of a measurement of a physical quantity, it is obligatory that some quantitative indication of the quality of the result be given so that those who use it can assess its reliability. Without such an indication, measurement results cannot be compared, either among themselves or with reference values given in a specification or standard. ” -Bureau International des Poids et Mesures (BIPM) BeyondTheBasics USMN Getting Located in SA 32 06

BeyondTheBasics USMN Getting Located in SA 33 06

BeyondTheBasics USMN Getting Located in SA Instrument Targeting Environment Operator Geometry Fixturing Scale Contributors to Uncertainty

Demo 3 Uncertainty analysis with USMN USMN2.xit64 Using UMSN to evaluate the uncertainty of two different measurement strategies Getting Located in SA 35 02

BeyondTheBasics USMN Getting Located in SA Parameters describing the uncertainty characteristics of a given measurement system. Uncertainty Variables

BeyondTheBasics USMN Getting Located in SA 37 06

We’d have to constantly update the values ourselves. One OEM would probably love us. The rest? The instrument is only a piece of the uncertainty. Your instrument is different than mine. Your environment is different than mine. Other factors we can’t determine for you. Why only provide general values? BeyondTheBasics USMN Getting Located in SA 38 06

1. Establish network of eight (8) or more fixed monuments. 2. Locate instrument at four (4) or more stations, measuring common points at each station. 3. Perform a USMN on the network to calculate the uncertainty variables. 4. Copy resulting values into your instruments during the actual survey. Uncertainty Variable Determination General Steps: BeyondTheBasics USMN Getting Located in SA 39 06

BeyondTheBasics USMN Getting Located in SA Measured survey with multiple instrument stations and at least 8 common targets.

Demo 4 Advanced USMN USMN3.xit64 Using USMN to determine measurement system uncertainty Getting Located in SA 42 06

Questions? We have answers! Getting Located in SA 43 Zach Rogers NRK, EMEAR Application Engineer