(Above example of a photogrammetry capture of a Dali Sculpture made by Jonathan Yomayuza of Emblematic Group)
Photogrammetry is the building of a 3D point cloud based on a sequence of photos taken from different positions and angles. Stitching a 3D object relies on figuring out where similar points are located in space and from where it was taken in the space.
SETTING UP YOUR CAMERA
- A DSLR or mirrorless camera with a large sensor is preferred for high fidelity projects. But a point and shoot in manual mode will work just fine.
- Keep exposure settings consistent throughout the shoot. The lower the ISO (less noise) the better.
- SHOOT RAW
- We’ve gotten decent results with a fixed focal lens like a 35mm prime, if you use a variable focal length lens, just keep it at one focal length. Extreme wide angle lenses (14mm or wider) are not preferred because of the distortion.
- If you’re shooting a room with a tall roof or a tall cave, zooming in to the roof details is recommended, but take pictures as you zoom in so that the stitching software can locate where you are in the space
- Tripod / monopod? If you’re shooting at less than 1/30 second, shooting with a tripod will help eliminate blurriness, just make sure to move the tripod around the room and to change the height to make sure you’re getting complete coverage of the space. We think a monopod will let you move around plenty while getting a stable enough hand.
WHERE TO START
The ideal subject, environment or object is not too dark nor reflective. Definitely avoid glass. If you’re doing an outdoor area, set a mental boundary of where to drop off.
- It generally doesn’t matter where you start. As you circle around the room or area, make sure you end where you start. Try to get overlap between photos. More overlap will result in a tighter, more accurate 3D model.
- Start by walking along the circumference of the room and shooting the circumference wide — just to get an overall capture of the space — and then doing the same loop but angling your camera and the bottom of the room and then making a loop and after each look angling up the camera 20 more degrees and repeating that until you get to the top.
- Instead of capturing photos from the middle of the room and rotating around, move along the walls and take pictures in the other direction. In doing so, more angles are captured that helps with the calculation process.
- Take as many photos as possible, the software we use (RealityCapture) has no limit. For a sculpture that we scanned we found about 1,000 images provided a clean model
- For little details take at least 5 photos.
- A room with diffuse “global” light that does not produce high contrast shadows. Not illuminated by a spotlight, but an omnidirectional soft light
- Do not use the camera flash. Flash can make every photo different in terms of lighting exposure, which is not recommended for the photogrammetry process.
- Environments with strong casting shadows should be avoided. Shadows don’t work well for the reconstruction process as there aren’t many features that can be matched for reconstruction.
- Avoid shooting at midday under bright sun. Best times are early in the morning, later in the afternoon, or on overcast days. Overcast days are pretty ideal.
- Environments that are highly reflective can be confusing for stitching algorithms. Ideally a space with matte objects and lots of texture will work well.