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Verification of specifications and aptitude for short-range applications of the Kinect v2 depth sensor Cecilia Chen, Cornell University Lewis’ Educational and Research Collaborative Internship Project (LERCIP) NASA Glenn Research Center, Graphics & Visualization/Dr. Herb Schilling 7/22/2014

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Purpose of this study Validate the published specifications for the Microsoft Kinect v2 depth sensor Resolution and x-y position accuracy Depth-sensing accuracy Near-range sensing limit Determine the sensor’s potential for use in short-range applications Feasibility of repurposing the Kinect for functions requiring an operating distance of approximately 0.5 m from the sensor

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Overview of topics discussed I.Introduction A.Microsoft Kinect v2 B.Infrared and Depth streams C.Time-of-flight II.Preliminary Calculations A.Is the depth camera’s error range acceptable? B.Possibility of errors in position due to low resolution C.Possibility of errors in angle due to noise

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Overview of topics discussed III.Calibration and Experimental Verification A.Software preparation B.Calibration C.Experimental verification IV.Conclusions A.Findings B.Sponsors

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Introduction

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Microsoft Kinect v2

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Infrared and Depth streams

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Time-of-flight

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Preliminary Calculations

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Is the depth camera’s error range acceptable? Microsoft claims depth measurements are accurate to within 1 mm Guidelines for short-range use of the depth sensor Defined by an operating distance (between the Kinect and object) of approximately 0.5 m Near-range of the Kinect v2 supposedly starts at 0.5 m Given a surface oriented perpendicular to the depth axis: Position – be able to locate a point on the surface to within 2 mm Angle – be able to measure inclinations on the surface to within 10° Both to be confirmed through calculations using an upper error bound

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Possibility of errors in position due to low resolution y z x

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35 ° x/2 0.7 m x/2 35 ° Horizontal slice of FOV

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Possibility of errors in position due to low resolution y/2 0.7 m y/2 30 ° Vertical slice of FOV 30 °

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Possibility of errors in position due to low resolution

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50 mm diameter

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Possibility of errors in angle due to noise For simplicity, take a plane defined by two points 50 mm apart representing the same circular surface: 50 mm diameter x y z Axis orientation

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Possibility of errors in angle due to noise z x y 50 mm Kinect θ ΔzΔz

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Possibility of errors in angle due to noise ΔzΔz 50 mm θ

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Calibration and Experimental Verification

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Software preparation Use C# to interact with Microsoft Visual Studio and the Kinect for Windows SDK Modify and expand the Depth Basics code included in the SDK (Preview 1404) Decreasing the grayscale gradient range for easier visual distinguishability between depths Making the window recognize a hovering cursor Writing the (x, y, z) coordinates of the cursor to the image window in real-time Averaging depth readings at a given point to smooth out jumpy data Capturing depth arrays of multiple frames Outputting collected data to CSV files for further analysis

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BeforeAfter

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Calibration Step 0: Design and assemble a rig to hold the Kinect steady Step 1: Level the sensor Step 2: Set up a base surface for measurements at a height similar to the intended distance between the Kinect and interaction area

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Calibration Step 3: Check for irregularities

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Experimental verification Step 4: Measure a sloped calibration block of known height 50 mm

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Base, z 1 Top of block, z 2 Height, Δz Actual (mm)-- 50 Measured (mm)5710 (538 minimum)Error

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Experimental verification Step 5: Lower the base height Step 6: Measure a sloped calibration block of known height 50 mm

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Base, z 1 Top of block, z 2 Height, Δz Actual (mm)-- 50 Measured (mm)

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Experimental verification Step 7: Repeat with calibration block(s) of different heights 64 mm

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Base, z 1 Top of block, z 2 Height, Δz Actual (mm)-- 64 Measured (mm)

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Conclusions

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Findings Successful verification of the published specs Kinect v2 appears to be a promising depth sensor for short-range applications Expectation or Guideline Experimental confirmation Acceptable? Position (resolution)±2 mm(1.9 mm) 2 per pixel resolution Yes Angle (noise) ≤ 10°Requires Δz ≤ 8.8 mm at z = 0.7 m Very Depth accuracy±1 mm Very Near-range0.5 m0.538 mNo

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