Visual Optimality And Stability Analysis Of 3DCT Scan Positions
Artem Amirkhanov 1,2
Michael Reiter 2
Christoph Heinzl 2
M. Eduard Gröller 1
1 Institute of Computer Graphicsand Algorithms
Vienna University of Technology
2 Upper Austrian University of Applied Sciences
Wels Campus, Austria
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Scanning Geometry
X-ray source
Specimen
Detector
Rotary plate
Placement is crucial forMeasurements accuracy
Iso-surface quality
Requires knowledge, intuitive
Good placement is hard to findFor a complex specimen
For measurement features
Doing several scans is expensive
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Specimen Placement
CAD model is availableQuality control – from manufacturer
Reverse engineering – preliminary scan
Use a CAD model to estimate a good placement
Visual analysis tool is required forSimulation-based preview
Optimal placement estimation
Tool
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Motivation
Optimal Placement
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Why Placement is Important?
Beam-hardening artifactsCupping artifacts
Streaks
Bad planar faces artifactsBlurring
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Good/Bad Placement Example
Bad:
Good:
Shortest penetration lengths Method: ray casting
Smallest bad planar faces areaMethod: Radon-space analysis
Stable within a certain range of reliabilityMethod: stability widget
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Criteria and Methods
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Workflow
• Ray casting• Radon-space analysis
Simulation
• Stability analysis• Data exploration and analysis
Visual analysis
Optimal placementOptimal placement
CAD modelCAD model
ParameterspacesParameterspaces
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Simulation
Set of candidate placements
Placement is defined by the orientation
Orientation is defined by two Euler angles α and β
α
β
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Ray Casting Simulation
Reflects the scanning setup
Set of projections for every placement
ParametersMaximum penetration length
Average penetration length
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Radon-Space Analysis
Supporting planes → points in Radon space
Finding bad points in Radon space
ParameterBad faces area percentage
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Parameters Representation
Best Worst
Parameter value:
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Stability Widget
Better Same Worse
Parameter value:
Penetration-length histogramsVisualizing ray subsets .
Color coding bad faces .
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Data Visualization and Exploration
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Evaluation Using Dimensional Measurements
Two test-part specimens
Measurement featuresRadius
Distance
CALYPSO used to estimate measurement quality
Complex real world specimen
Best and worst placements
Variance comparison of the iso-surfaces with the CAD model
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Evaluation Using Variance Comparison
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Evaluation
Bad Placement Good Placement
Position deviation spectrum in [mm] Position deviation spectrum in [mm]
0 -1 -22 1 0 -1 -22 1
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Limitations and Future Work
Orientation onlyDetect orientation and position in sequence
Still requires user interactionCombining parameters
