1. Dec. 2016 Visualization with 3D CG
PhotoScan Workshop
Masaki Hayashi

2. Photogrammetry Many software available
Comparison of photogrammetry software (Wikipedia)
123D (Autodesk)
Recap360 (Autodesk)
ReMake (Autodesk)
PhotoScan (Agisoft)
Good quality
Server side engine
Free to use (student)
Standalone local engine
Good quality, too
Commercial software(179$ - )

3. Choose appropriate object
In order to get good quality
Whatever software you're using:
Choose appropriate object
Too much convex-concave
All black
(no texture)
Shiny, transparent

4. Prepare good pictures In order to get good quality
Whatever software you're using:
Prepare good pictures

5. Reason for the need of good pictures
In order to reduce errors in obtaining feature points.
error
Uses image processing algorithm to get as much feature points on a given images.
Searches the corresponding feature points automatically.
Generally, it produces a lot of errors.

6. Good picture for photogrammetry
Good focus (deep focus)
Ways to get deep focus
1) Short focal length =>
Do not use much zooming in
Set camera closer to the object
Use bigger object
2) Small aperture (big F-number) =>
Do in a bright room (cloudy is better)
Use much light
Use big ISO, but not so much

7. Good picture for photogrammetry
Good focus (deep focus)

8. Good picture for photogrammetry
Focal length
The software has standard focal length assumption.
=> 35mm equivalent focal length = 50mm
In CANON EOS 7D, this is about 35mm focal length lens.
PhotoScan uses EXIF to get its focal length for calculation. If EXIF is not available, the software assumes that the picture is taken at "35mm equivalent focal length 50mm".
It's safe to use the standard focal length when filming.
EXIF: meta data attached to image file

9. Good picture for photogrammetry
Exposure
Basically, constant exposure is better.
=> Use manual exposure
First decide ISO and F-number.
F-number should be big (than 15) to get deep focus.
Then, decide shutter speed.
If the shutter speed is less than 1/30, use tripod to clamp the camera to avoid blur.

10. Good picture for photogrammetry
Exposure has three factors.
ISO Less than 200 is better in terms of noise.
(Bigger, brighter) Sometimes 500 is needed, but not more
than 800. (much noise on the image)
F-number Not less than 15.
(Lesser, brighter) (otherwise narrow focus, blur)
Shutter speed If it's hand-held, not slower than 1/30.
(Slower, brighter) If tripod is used, doesn't matter.

11. Good picture for photogrammetry
Full size to get enough resolution of the object.
Get closer to the object, not using zoom.

12. Good picture for photogrammetry
Many pictures as possible
Generally, more than 30 pictures (minimum 20)
=> 360-degree + different angles
(don't change the filming condition. i.e. focal length, exposure, etc.)
different angle
360-degree

13. Process of PhotoScan Camera alignment Build dense cloud Build mesh
If camera alignment badly failed, try use Mask.
If some of the cameras failed, try "Reset camera alignment" and retry "Align selected cameras" of the target cameras.
If the error persists, try use Marker.
Crop and clean the sparse point cloud before doing "Build dense cloud".
Also, clean the dense point cloud before building mesh.
If much holes appear, try use an option "extrapolated" in "Advanced option".
Camera alignment
Build dense cloud
Build mesh
Build texture

14. If you want the bottom Use "Chunk"
Film top view and bottom view respectively and assign them to two different chunks.
Then, merge two chunks by using Markers.