Rigid Features and Three-View Overlap
Photosynth constructs a 3D model by recognizing features (distinct points, usually) present in three or more photographs taken from different places. We call this the three-view overlap, and without it, Photosynth fails.
Parts of the scene that move are challenging to Photosynth. It really needs lots of rigid features (things that stay where they are in the world from shot to shot) to do its 3D magic. That’s why people who are walking or even turning their head between shots aren’t modeled properly. They stay in the photos, but as your viewers move through the resulting synth, the transitions are a little rough. Here’s an example highlighting these issues:
Other parts of the scene that move (such as water, or leaves in a breeze) or are fairly featureless (such as a big white wall) also do not help the 3D reconstruction. These things can be part of the scene, though, and as long as there are enough rigid features with three-view overlap, Photosynth can still construct a synth.
Photosynth requires at least three photos to make a synth, and there is a current maximum of 200 photos per synth. You’ll have fewer artifacts in the viewing experience if you use more photos. However, shooting so many photos that there is only a tiny difference between successive images (for example, a spin of 100 photos) is counterproductive. The viewing experience suffers from the extra images. Use up to 200 photos in a walk or a wall only if you need that many to cover the space with three-view overlap. For spins and panoramas, don’t exceed 60 shots.
Spins and panoramas often connect into full 360-degree loops, but walks and even walls can also form loops if the shape of the space you’re capturing permits. If you are planning to shoot a loop, it’s a good idea to mark the ground with your starting point so that you can return to the exact place you started. If you don’t, it’s very easy to spiral in or spiral out as you complete the loop, resulting in a jarring jump as somebody views the transition between your last image and your first one. Here's an example of a looped walk:
Photosynth pays attention to the “Date Taken” field in the EXIF of your photos, and it always tries to match the features of a photo with the features in the photos taken immediately before and immediately after the current one. Do not be tempted to skip sections of your path and come back to them later. If you do, you’ll end up with only a partial result.
Depth of Field
Don’t shoot a deep scene with a very narrow depth of field. The Bokeh effect looks beautiful to our eyes, but doesn’t give Photosynth the features it needs to do its reconstruction. Try to keep to an aperture of F4.0 or above unless dealing with a flat wall. Aside from that, you don’t need to keep your aperture constant as you move through the scene.
Although we do not yet put your synths on a map, we expect this capability to come relatively soon. So, don’t strip any GPS data from photos of any synth you would like to display on a map in the future.
Part 4 focuses on tips for spin synths.