EQUIPMENT
For quick shoots, any digital camera will do, including cellphone cameras. But for a controlled shoot, I recommend:
– 50mm lens
– Tripod (depending on conditions)
– Remote shutter release (if using tripod)
– Strong, diffuse lighting
– Polarizing filter (for shiny objects)
– Measuring tape
– Blue masking tape
ENVIRONMENT
Strong, very diffuse light is best. Harsh shadows can create problems.
A motionless, non-reflective, and varied background is good. The more random features there are in the background, the better the system can track points and triangulate.
A monochrome, uniform, featureless background can be problematic. Add clutter or tape marks to the background.
Repeating patterns on carpet or wallpaper are problematic.
SUBJECT
Light-colored, matte materials with some color variation are best. Dull, weathered stone is ideal.
Shiny, reflective surfaces are problematic. A polarizing filter may help reduce specularity in some cases. Dark, shiny bronze statues are very challenging.
EXPOSURE
Use as low an ISO setting as possible, to reduce noise. The software actually matches pixels to pixels from one photo to the next, so sensor noise creates a lot of problems.
Use as small an aperture as possible (high F-stop). The foreground and background both need to be in focus.
Use a tripod and remote shutter release for longer exposures.
If using a high F-stop is not possible, and the background cannot be kept in focus, at least try to keep the subject itself entirely in focus. Filling the frame with the subject can also improve results if a lower F-stop must be used.
SHOOTING
Take a measurement of a linear feature of the subject, or something in the background that will also be picked up in every shot. If feasible, place an object with a straight edge and known size in the scene, near or against the subject, and leave it there for the duration of the shoot. Don’t move it during the shoot. These will provide scale references.
Before shooting, find a distance from and path around the subject and a single zoom length that will allow you to take all your photos without adjusting the zoom. Avoid getting so close that you see big lensing/fish-eye or perspective and foreshortening distortions.
When shooting, don’t change the zoom ring at all. This is critical—you can move the entire camera closer or further away from the subject as needed, but don’t change the lens or exposure settings at all from shot to shot, as doing so will ruin the survey.
Try to have the subject fill the frame as much as possible.
Rotating the camera from shot to shot—from portrait to landscape or anything in between—is OK.
The light source cannot change or move relative to the subject at all from shot to shot. Don’t use a mobile flash. Any light source or flash needs to be fixed relative to the subject.
Take at least three laps around the subject, shooting from medium, high, then low angles, keeping the entire subject in frame. Then for additional close-up detail shots, take additional laps around the subject while aiming the camera so that the lens’ line of sight is perpendicular to the surface of the subject in the frame.
Take all photos in sequence—each shot should overlap with its neighboring shots. Don’t jump around the subject.
Every point on the subject must be in at least one series of at least three consecutive shots. The more series, from multiple angles, and the more consecutive shots per feature, the better the system can match points.
Make sure to take photos of features that are obscured by other features.
If you want to try different exposure settings, treat each shoot as a completely new photoshoot. Never mix settings between complete shoots. Take a photo of something between settings changes so that later you can see at a glance where the different exposure sets start and stop.
PROCESSING
Don’t edit the photos in any way. No cropping, re-sizing, levels adjusting, or masking.
When uploading, start with the shots that loop around the subject while keeping the subject completely in frame. Low, medium, and high angles. Then add any detail shots.
FUTURE-PROOFING
If practical, shoot in RAW, in addition to JPG. Some applications may be able to get better results with different JPG compressions of the original RAW files.
Shoot more photos than current software requires. You may get better results from set-to-set, or from different loops around the object within a set. More powerful applications may soon be able to get better results with more shots, so you may as well take as many as practical instead of going back and starting over a year later when more powerful software is available.
COSMO WENMAN 