Aerial 3D photogrammetry is easy-to-use and low cost for 3D modelling and mapping. However, there are certain limitations and weaknesses in capturing photos and reconstructing 3D models with this technology. We would like to share a few examples below to understand some common mistakes and learn the best practice of how it works.
Object Too Small
If you shoot an object too far away, it occupies only a small portion of the photo (like the sample below occupying less than 1/20 of the photo). It wastes most of photo resolution and valid pixels. 12M pixels DJI camera turns out to 0.6M effective resolution. You are likely to get a blurry model, due to insufficient valid points for photogrammetry.
The sample below occupies 2/3 of photo area and utilizes most of valid pixels of photos. You are recommended shooting as close as possible to the object for maximizing valid pixels.
FOV indicator (a blue semi-transparent triangle) is a good tool to show horizontal camera FOV angle shooting from aircraft to target. It helps you to set the proper radius covering the object, but not too far away from the object.
If you shoot in early morning or late afternoon, one direction of photos are shooting into sun. This might cause some photos under exposure, and incur blurry model. The other direction of photos might have obvious shadow though it wouldn't impact the model quality.
Shooting around noon on a slightly cloudy day (with diffuse lighting) usually works the best for 3D model.
Avoid Thin or Transparent Object
Avoid reflective, shiny, transparent, thin or moving objects, such as glass and water. Those objects and thin frames are unlikely to be reconstructed in photogrammetry.