Jan. 2014Visualization with 3D CG

Masaki Hayashi

Digitization

Today’s contents

• Digital camera• Laser scanning• Photogrammetry

(break)

• Agisoft “Photoscan” + Filming

Digital camera

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:

Spec of digital camera

Focal lengthFixed or Zoomhuman eye sight ≒ 50mm (35mm film equivalent)

ResolutionLens flareLens ghostingDistortion

Optical aberrationBarrel Pincushion

Lens:

Ghosting

Flare

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:

Lighting

Fill light

Main light

Back light

Translucent backdrop (white and frosted plate)

artifact

Camera

(from the bottom)

Laser scanning

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)

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

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)

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)

Laser scanning

• Multiple measurements: Compensation of the shadow

Planning:• Locations• Angle of view• Resolution

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:

Laser scanning

Minolta-Konica Vivid 9i

Example video http://youtu.be/YpcGmh85Hes

Laser scanning

Some scenes

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:

Photogrammetry

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

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.

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)

Recent tech

Better Reality : Thorskan

Recent tech