Download - Jan. 2014 Visualization with 3D CG
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Jan. 2014Visualization with 3D CG
Masaki Hayashi
Digitization
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Today’s contents
• Digital camera• Laser scanning• Photogrammetry
(break)
• Agisoft “Photoscan” + Filming
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Digital camera
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Spec of digital camera
8 megapixels (=8,000,000) :iPhone18MP :Consumer digital camera60MP :Hasselblad
Consumer: approx. 16MP to 24MPHasselblad : 40MP to 60MP
8M: 3465x230918M: 4896x367260M: 8944x6708
Requires good lens for high-resolution
Resolution:
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Spec of digital camera
Focal lengthFixed or Zoomhuman eye sight ≒ 50mm (35mm film equivalent)
ResolutionLens flareLens ghostingDistortion
Optical aberrationBarrel Pincushion
Lens:
Ghosting
Flare
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Spec of digital camera
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- UncompressedEtc.
Bit depth:
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Lighting
Fill light
Main light
Back light
Translucent backdrop (white and frosted plate)
artifact
Camera
(from the bottom)
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Laser scanning
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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)
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How does 3D Scanner work?
• Short-range ( < 1 m ) Laser triangulationStructured light
• Middle-range (10m)Travel Of Light (TOL): Phase shift
• Long-range ( > 100m )Travel Of Light (TOL): Pulse
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Short-range ( < 1 m )
Laser triangulation
SensorLens
Object
Laser
Structured light
Known
Calculated by 3 values
Measured Measured
L sinβsin (α + β)D =
(α) (β)
(L)
(D)
SensorLens
Object
Linear patterns
Triangulation
(more accurate)
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Long-range ( 100 m )
TOL (Travel Of Light)
Sensor
Lens
Object
Laser Measure the TOLc (m/sec) = 299,792,458
Out
In
TOL TOL (phase)
Out
In
Pulse modulation Phase modulation(more accurate)
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Laser scanning
• Multiple measurements: Compensation of the shadow
Planning:• Locations• Angle of view• Resolution
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Laser scanning
• 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
Error:
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Laser scanning
Minolta-Konica Vivid 9i
Example video http://youtu.be/YpcGmh85Hes
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Laser scanning
Some scenes
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Laser scanning
• 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
Post-processing:
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Photogrammetry
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Photogrammetry
Good point: Texture color is more realistic.Bad point: More errors.
• 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
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How does photogrammetry work?
Camera
Object
3D position can be calculated if the camera parameters are knownby triangulation
Camera
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.
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Photogrammetry
Some points:
Field of ViewStandard : 50 degreesTendancy: Less accurate with wider lens
FocusingTo get enough depth of field
Lens distortionYou may need to measure the distortion
Reflective materialCauses the error regarding the feature points
ScalingPhotogrammetry measurement is dimensionless
AccuracyAccurate in “x-y”, not so much for “z” (laser scanning has better accuracy of Z)
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Recent tech
Better Reality : Thorskan
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Recent tech