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Jan. 2014 Visualization with 3D CG

Jan. 2014 Visualization with 3D CG. Digitization. Masaki Hayashi. Today’s contents. Digital camera Laser scanning Photogrammetry (break) Agisoft “ Photoscan ” + Filming. Digital camera. Spec of digital camera. Resolution: . 8 megapixels (=8,000,000) :iPhone

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Jan. 2014 Visualization with 3D CG

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  1. Jan. 2014Visualization with 3D CG Digitization Masaki Hayashi

  2. Today’s contents • Digital camera • Laser scanning • Photogrammetry(break) • Agisoft “Photoscan” + Filming

  3. Digital camera

  4. Spec of digital camera Resolution: 8 megapixels (=8,000,000) :iPhone 18MP :Consumer digital camera 60MP :Hasselblad Consumer: approx. 16MP to 24MP Hasselblad : 40MP to 60MP 8M: 3465x2309 18M: 4896x3672 60M: 8944x6708 Requires good lens for high-resolution

  5. Spec of digital camera Lens: Focal length Fixed or Zoomhuman eye sight ≒ 50mm (35mm film equivalent) Resolution Lens flare Lens ghosting Distortion Flare Ghosting Optical aberration Barrel Pincushion

  6. Spec of digital camera Bit depth: • 8 bit (eg: compact consumer: JPEG, TIFF) • 12,14 bit (eg: high-end consumer: RAW) • 16 bit (eg: Hasselbad: RAW) • With RAW data, you can adjust (Processing) • - Dynamic range (lightness) • Color temperature (white balance) • Edge enhancement • Uncompressed • Etc.

  7. Lighting Translucent backdrop (white and frosted plate) Back light Fill light artifact Camera Main light (from the bottom)

  8. Laser scanning

  9. Laser scanning • Range: Very small object(eg. tooth), Middle (eg. • Statue), Very large (eg. ruin, city landscape) • + Aerial (Huge area) • Output: 3D point cloud, basically. • x, y, z coordinates • + I(intensity) + r, g, b(color)

  10. How does 3D Scanner work? • Short-range ( < 1 m ) Laser triangulation Structured light • Middle-range (10m)Travel Of Light (TOL): Phase shift • Long-range ( > 100m ) Travel Of Light (TOL): Pulse

  11. Short-range ( < 1 m ) Laser triangulation Laser Lens Sensor Triangulation (L) Known Measured Object Measured (β) (α) Structured light (D) (more accurate) Linear patterns Calculated by 3 values Sensor Lens L sinβ sin (α + β) D= Object

  12. Long-range ( 100 m ) TOL (Travel Of Light) Measure the TOL Laser c (m/sec) = 299,792,458 Sensor Lens Object Out Out In In TOL TOL (phase) Pulse modulation Phase modulation (more accurate)

  13. Laser scanning • Multiple measurements: Compensation of the shadow • Planning: • Locations • Angle of view • Resolution

  14. Laser scanning Error: • Beam expansion Spot diameter is bigger when range is biggereg. 12mm at 5m  97mm at 500m • Depending on materialDiffuse on the surface (clod, solid, reflective…) • Angle of the beam when the beam strikes the surface

  15. Laser scanning Example video http://youtu.be/YpcGmh85Hes Minolta-Konica Vivid 9i

  16. Laser scanning Some scenes

  17. Laser scanning Post-processing: • Cleaning of point cloud and filtering of the noise • Point cloud to polygon conversion • Filling of holes of the mesh • Elimination of abnormal faces • Decimation • Texturing • Exporting

  18. Photogrammetry

  19. Photogrammetry • Range: Almost same as scannerSmall object(eg. vase), Middle (eg. • Statue), Very large (eg. ruin, city landscape) • + Aerial (Huge area) • Output: 3D point cloud + Color • x, y, z + r, g, b Good point: Texture color is more realistic. Bad point: More errors.

  20. How does photogrammetry work? Camera Camera 3D position can be calculated if the camera parameters are known by triangulation Object Camera parameter: x, y, z, rx, ry, rz, AngleOfView Known points (Feature point) All the calculation is automatically done at a time Don’t get the software confused to get feature points.

  21. Photogrammetry Some points: Field of View Standard : 50 degrees Tendancy: Less accurate with wider lens Focusing To get enough depth of field Lens distortion You may need to measure the distortion Reflective material Causes the error regarding the feature points Scaling Photogrammetry measurement is dimensionless Accuracy Accurate in “x-y”, not so much for “z” (laser scanning has better accuracy of Z)

  22. Recent tech Better Reality : Thorskan

  23. Recent tech

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