1. Accuracy of 3D Scanning Technologies in a Face Scanning Scenario Chris Boehnen and Patrick Flynn University of Notre Dame

2. Overview Scanner Overview Scanner Overview Defining Scanner Performance Defining Scanner Performance Experiment Method Experiment Method Results Results Conclusions Conclusions Future Work Future Work

3. 3Q From 3DMD Designed for faces Designed for faces Uses four cameras in two camera pods with a flash pattern to capture the 3D data in 2 milliseconds Uses four cameras in two camera pods with a flash pattern to capture the 3D data in 2 milliseconds Two camera pod system allows for coverage from ear to ear, but limited focal range Two camera pod system allows for coverage from ear to ear, but limited focal range

4. FR1 Vendor left anonymous because evaluated scanner does not represent their most current technology Vendor left anonymous because evaluated scanner does not represent their most current technology Uses a projected infrared pattern and a single camera to capture the 3D in real time Uses a projected infrared pattern and a single camera to capture the 3D in real time Designed for faces and biometrics Designed for faces and biometrics Fixed focal range Fixed focal range Infrared pattern makes it very robust to lighting variation Infrared pattern makes it very robust to lighting variation IR Camera IR Projector

5. FR2 Vendor left anonymous because evaluated scanner does not represent their most current technology Vendor left anonymous because evaluated scanner does not represent their most current technology A series of visible light patterns are projected over 20 seconds and 3 cameras calculate the 3D A series of visible light patterns are projected over 20 seconds and 3 cameras calculate the 3D Visible Light Projector Camera Has a limited focal range and is sensitive to lighting conditions Has a limited focal range and is sensitive to lighting conditions

6. Konica Minolta 910 Utilizes a camera and laser stripe Utilizes a camera and laser stripe Needs subject to hold still for 2.5 seconds during scan Needs subject to hold still for 2.5 seconds during scan Different zoom lenses help give it a large focal range Different zoom lenses help give it a large focal range Works well in different lighting conditions Works well in different lighting conditions

7. Polhemus Fastrak Uses a magnetic field to track the location of the wand (fixed laser stripe and camera) which is manually moved over the object Uses a magnetic field to track the location of the wand (fixed laser stripe and camera) which is manually moved over the object Person must stay still during scanning which takes ~30s depending on quality and operator Person must stay still during scanning which takes ~30s depending on quality and operator

8. Defining Scanner Performance Level of detail Level of detail Repeatability Repeatability Accuracy to scanned object Accuracy to scanned object Percentage of object captured Percentage of object captured Texture image Texture image Impact of environment Impact of environment

9. Accuracies We Explore Here Absolute Accuracy - the accuracy of the scanner with respect to a physical reference object Absolute Accuracy - the accuracy of the scanner with respect to a physical reference object Repeatability Accuracy - the degree of consistency between scans Repeatability Accuracy - the degree of consistency between scans Pose Variation Accuracy – As the orientation of the scanner to the object changes how does the data change Pose Variation Accuracy – As the orientation of the scanner to the object changes how does the data change

10. Experimental Method Use synthetic face masks of known ground truth as scanned objects Use synthetic face masks of known ground truth as scanned objects Allow each scanner to perform the scans under its own ideal conditions Allow each scanner to perform the scans under its own ideal conditions Compare resulting scans to each other and known ground truth Compare resulting scans to each other and known ground truth

11. Synthetic Face Masks An initial scan of a face from the Minolta is cleaned to produce the ground truth for the mask An initial scan of a face from the Minolta is cleaned to produce the ground truth for the mask 10 faces, five female and five male from different ethnicities are used for the initial scan 10 faces, five female and five male from different ethnicities are used for the initial scan A mold for the mask is produced using a Thermojet rapid prototyping machine from 3D Systems and a durable 2 part polymer is poured in A mold for the mask is produced using a Thermojet rapid prototyping machine from 3D Systems and a durable 2 part polymer is poured in The ground truth was verified with a tactile scanner and found to be ~0.018mm The ground truth was verified with a tactile scanner and found to be ~0.018mm

12. Data Collection Overview Capture a series of scans on each scanner under their ideal conditions Capture a series of scans on each scanner under their ideal conditions Run Raindrop Geomagic’s cleaning algorithm on the scans Run Raindrop Geomagic’s cleaning algorithm on the scans Perform an initial alignment to the scans and the ground truth Perform an initial alignment to the scans and the ground truth

13. Data Capture

14. Comparing Scans Visualization Toolkit’s implementation of ICP is run to align the scans as closely as possible Visualization Toolkit’s implementation of ICP is run to align the scans as closely as possible The distance from each point on one surface to the other is used to calculate the mean and Root Mean Square (RMS) error distances The distance from each point on one surface to the other is used to calculate the mean and Root Mean Square (RMS) error distances

15. Absolute Accuracy Comparisons

16. Repeatability Accuracy Comparisons

17. Results Overview Error values are in mm

18. Results Pose Change Error values are in mm

19. Outlier Detection and Removal We identified outliers as anything with a distance of over 20mm We identified outliers as anything with a distance of over 20mm

20. Conclusions The most accurate scanner here in every category is the Minolta followed closely by the 3DMD and Polhemus with the anonymous vendors far behind The most accurate scanner here in every category is the Minolta followed closely by the 3DMD and Polhemus with the anonymous vendors far behind In a real world setting the 3DMD may provide slightly more accurate data with live moving subjects, but has a sufficiently lower LOD that we ranked it second here In a real world setting the 3DMD may provide slightly more accurate data with live moving subjects, but has a sufficiently lower LOD that we ranked it second here

21. Conclusions The Polhemus scanner provided good data and is the smallest scanner here by far leaving open the possibility for a portable version The Polhemus scanner provided good data and is the smallest scanner here by far leaving open the possibility for a portable version FR1 provided a decent accuracy rating but the number of points was so low that we ranked it fourth here FR1 provided a decent accuracy rating but the number of points was so low that we ranked it fourth here FR2 has a high LOD but the accuracy of those points is very low and is ranked last here FR2 has a high LOD but the accuracy of those points is very low and is ranked last here

22. Future Work Addition of more scanners Addition of more scanners Exploring impact of color on accuracy Exploring impact of color on accuracy More realistic representation of skin material in face masks More realistic representation of skin material in face masks

25. Verifying the Ground Truth The Thermojet lays semi-rectangular dots of material with a diagonal of 0.11mm The Thermojet lays semi-rectangular dots of material with a diagonal of 0.11mm At worst parts of the model are only accurate to half the diagonal, but on average the model should be accurate to around.03mm At worst parts of the model are only accurate to half the diagonal, but on average the model should be accurate to around.03mm Using a tactile scanner operating on a 100 micron grid (1.5 million points), and accounting for systematic scanner error, we verified the models to be within approximately 0.018mm Using a tactile scanner operating on a 100 micron grid (1.5 million points), and accounting for systematic scanner error, we verified the models to be within approximately 0.018mm

26. Graphical Depictions of Accuracy

27. Scanner Review