Daily Note : Fluorescent Filaments to Embed Trackable Markers in 3D Printed Objects

These notes are a summary of concepts presented in “BrightMarker: 3D Printed Fluorescent Markers for Object Tracking.”

Mustafa Doga Dogan, Raul Garcia-Martin, Patrick William Haertel, Jamison John O’Keefe, Ahmad Taka, Akarsh Aurora, Raul Sanchez-Reillo, and Ste- fanie Mueller. 2023. BrightMarker: 3D Printed Fluorescent Markers for Ob- ject Tracking. In The 36th Annual ACM Symposium on User Interface Software and Technology (UIST ’23), October 29–November 01, 2023, San Francisco, CA, USA. ACM, New York, NY, USA, 13 pages. https://doi.org/10.1145/3586183. 3606758

  1. System Elements
    • Method involves embedding trackable markers in 3D-printed color objects using fluorescent filaments
    • Infrared-fluorescent filament shifts the wavelength of incident light for optical detection
    • High contrast markers enable robust tracking regardless of surface color
    • Applications
      • Motion capture: Digitizing physical objects and humans in real-time
      • AR/VR interfaces: Enhanced user experience with unobtrusive tracking
      • Wearables: Custom fabrication for natural and immersive experiences
  2. Optical Tracking Methods
    • Active markers
      • Use LEDs or IR sensors, requiring multiple cameras
    • Passive markers
      • Utilize retro-reflective beads
    • Integrated markers
      • Proposed to eliminate the need for external, manually attached markers
  3. Material and Fabrication
    • Fluorescent filament
      • Contains uniformly distributed fluorescent dye
      • Emits light in the near-infrared (NIR) range
    • Fabrication
      • Multi-material 3D printers use NIR-fluorescent filament in one print head
      • Colors like red, yellow, and orange have less opacity
    • Fluorimeter measurements
      • Determine excitation and emission spectra of the material
  4. Imaging System Components
    • Light source
      • Invisible to the user and excites fluorescent markers effectively
    • Optical filter
      • Isolates marker fluorescence and minimizes interference from other wavelengths
    • High-speed infrared camera
      • Monochrome with global shutter for precise and simultaneous image capture
  5. Marker Design and Configuration
    • Marker placement
      • Multiple markers ensure robust tracking independent of object orientation
    • Marker identification
      • Sequential IDs for unique identification and orientation
    • Marker depth and alignment
      • Aligned with the printing direction to reduce print failures and optimize time
  6. Hardware Modules
    • Smartphone attachment
      • USB-C connected module with LEDs matching filament excitation wavelength
    • Stand-alone module
      • AR/VR headset attachment for fluorescence imaging
    • Components
      • 60-fps NIR camera, LED grid, 9V battery, custom PCB
      • Total cost: $148; Weight: 118g
  7. Tracking and Decoding Process
    • Tracking markers
      • Grayscale images binarized using Otsu’s method
      • Contours identified and approximated as polygons
    • Decoding markers
      • Cropped patches resized, inverted, blurred, and thresholded
      • ArUco library used to decode marker IDs
    • Marker tracking across frames
      • Caching enables continuity by matching new and prior markers using corner coordinates
  8. Software Implementation
    • OpenCV: For tracking and binarization
    • Dynamsoft Library: For detecting 2D barcodes