Photogrammetry, Structure from Motion, and Drones

Photogrammetry is essentially photography based and is the act/science of gathering measurements of objects or buildings via photographs. These photos are then used to create two dimensional and three dimensional modeling. Once the photos are captured, they must be rectified to eliminate distortion in the photo using measurements from one plane.

Structure from motion is the act of creating three dimensional models based off of multiple photos. The structure model is based off of movement and documentation from multiple vantage points around the object. Using a program like Autodesk Recap, up to 250 photos can be uploaded and stitched together to generate a 3D model. A requirement for completing structure from motion is the inclusion of at least one measurement to ensure everything else is to scale. Photos collected must overlap each other by 50%, to ensure every detail is thoroughly captured. This entire process is automated on the server side, meaning the process is completed in a cloud rather than by hand. In the event of discrepancies, manual photo registration is possible. Positive benefits of  structure from motion include being less expensive than scanning, higher megapixels equating to better quality, and less time needed at the site. Drawbacks result from a decrease in accuracy from scanning.

Drones enable a perspective of historic buildings and objects that previously wasn’t available in standard documentation. Although drones are expensive and licensing may be necessary to operate in certain environments, they truly provide a great insight of sites from above, capturing more information and photographs than on the ground. Photographs collected from the air can then be uploaded into computer programs to be stitched together to create an in-depth 3D model.


Advice:

  1. Shoot sequential around buildings
  2. Have at least 50% overlap between images
  3. Be aware of occlusions
    • 5-10 degree intervals
  4. Shoot no more than 200 photos
  5. Create identifiable features if needed
  6. Symmetrical features/transparency/shiny surfaces may prove difficult
  7. Do not move object while photographing
  8. Consistent lighting is best/do not use flash

Image Sources:

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwjY3oSn_IjUAhUQcCYKHQjnAewQjxwIAw&url=https%3A%2F%2Fwww.linkedin.com%2Fpulse%2Fdrone-preservation-cultural-heritage-architecture-texas-jonathan-kohn&psig=AFQjCNE4pDIFYZELzl59RGjcr4Lt_sSNEw&ust=1495730436470049

http://www.preservationmaryland.org/drone-documentation-whites-hall-johns-hopkins-home/
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