Photogrammetry Project Example Including Flipping Object for Underside

In Photogrammetry, a good basic approach is to shoot a picture every 10 degrees, which makes for 36 pictures per revolution (360 degrees). Preferably, you want multiple camera angles. In this example, a rotating turntable is used to rotate the object. This allows for the lights to remain in one position for all of the photos. The camera can be mounted on a tripod. In this example, a DSLR was used (Canon T6s).

For lighting, one can use strobe lights, which are triggered by a transmitter in the hot shoe of the camera. Generally, it's good to have some form of diffusion on the lights to soften it so that the entirety of the texture is relatively flat and has no abrupt transitions in lighting. Another option is to polarize the lights, and utilize a polarizer filter on the lens, and creating a cross-polarized system, which eliminates shine and highlights (or significantly decreases them).

Here are the settings I used on the camera:

Aperture/F-Stop: f/10

Shutter Speed: 1/160th

ISO: ISO-400

Focal Length: 50mm

Generally, you want a high aperture to elongate the depth of field. Photogrammetry results are better when aiming for maximum focus versus maximum sharpness. The shutter speed should be as fast as your lights can handle (if you shoot too fast you see vignetting). The ISO should be as low as possible and only raised when shooting an object that is black. The focal length should not be too short or too long as too short causes distortion, and too long decreases surface visibility.

For preparation, it's recommended to elevate your object slightly so that your object and the ground directly beneath it aren't fused into the same geometry. Before you begin your project, you should have a strategy of how you will capture underneath the object. It is not always easy to fixture an object upside-down. It's possible you could just lay it on its side, but then you would need both sides, which increases the number of photos required.

For framing, the object should be within the frame and in the center, however, the closer you are, the more resolution you may attain on your object, which will increase detail. When you frame the object further away (and smaller in the frame), you will attain a better registration (alignment), however, you will also be losing megapixel resolution the further back the object is framed, which decreases detail.

These two pictures are a sort of calibration for a photo set. The first is for exposure; the grey card is 18% grey and helps find the correct exposure. The histogram should be directly in the middle, not touching either the left-or-right side. Secondly, there is a white balance calibration with a color palette. In your photo-developing software like Adobe Lightroom, you can use the color picker to select the light grey shade, and it will then have the proper color temperature and tint for that specific room's lighting. So, after the shoot, the whole photo set can be synchronized to the properly found white balance. This is what makes your texture look like real life. I recommend shooting in RAW format if you intend to 'sync the white balance'.

For this photoset, 195 photos were taken:

• object upright
  • 0 degree straight angle
  • 15 degrees high angle
  • 37.5 degree high angle
• object upside-down
  • 37.5 degree high angle
  • 15 degree high angle
  • 7.5 degree high angle

As you can see there were no low angle shots. This is because the 'low angle' is achieved by flipping the object and doing high angles. Although this object aligned nicely, there is a drawback of how I fixtured it when it was upside-down. The laces weren't visible due to a piece of foam the toe of the boot was resting on. This makes the laces look less detailed than if they weren't obscured.

Software instructions:

To help the software distinguish the different between the object upright and the object upside-down, I import each group separately, so that I have two photosets in the software.

1. Tools/AI Photogrammetry/Create Preview
   1. Photoset Capture Setup: Rotated/Moved In Each Photo
      1. Advanced Settings: 'Uncheck Fast Processing'
2. Tools/AI Photogrammetry/Create Model
   1. Processing Mode: AI
   2. Detail: Enhanced
3. Texture/Create
   1. Inpaint Missing Texture (checked)
   2. Output Texture Size: 8192x8192