Nov Visualization with 3D CG Masaki Hayashi PhotoScan Workshop

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

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

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

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". EXIF: meta data attached to image file It's safe to use the standard focal length when filming.

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 fix 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.) 360-degree different angle

Process of PhotoScan Camera alignment Build dense cloud Build mesh Build texture If camera alignment badly failed, try use Mask. If some of the camera failed, try "reset camera alignment" and retry alignment of the target camera, or try use Marker. Crop and clean the sparse point cloud before doing it. Also clean the dense point cloud before doing it. If much holes appear, try use an option "extrapolated" in "Advanced".

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.