Nov. 2017 Visualization with 3D CG PhotoScan Workshop Masaki Hayashi

Photogrammetry Many software available Comparison of photogrammetry software (Wikipedia): https://en.wikipedia.org/wiki/Comparison_of_photogrammetry_software 123D (Autodesk) Recap360 (Autodesk) ReMake (Autodesk) Good quality Server side engine Free to use (student) (Now it’s unified to “ReCap Photo”) PhotoScan (Agisoft) Standalone local engine Good quality, too Commercial software(179$ - )

1) Choose appropriate object In order to get good quality Whatever software you're using: 1) Choose appropriate object Too much convex-concave All black (no texture) Shiny, transparent

2) Prepare good pictures In order to get good quality Whatever software you're using: 2) Prepare good pictures

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.

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

Good picture for photogrammetry Good focus (deep focus)

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

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.

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.

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

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

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

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.