FAA Section 333 Exemption No. 12747A
General Overview of Photogrammetry:
Photogrammetry uses the process of Structure from Motion (SfM) to create 3-dimensional objects from 2-dimensional photographs. By taking many overlapping photographs, photogrammetry software can find common points within the photos and calculate the angles of the different photographs to those common points. If there is enough overlap between photographs and enough common points found, the software can reconstruct the 3-dimensional properties of the objects in the photographs and create a scaled, 3-dimensional model of the objects. There are many factors that determine the quality and accuracy of the models; such as, the type of camera used, the amount of overlap between photographs, the angles at which the photographs were captured, etc.: properly capturing the photographs is a skill acquired with experience. Once the photographs are captured, there is usually some post-processing required to obtain a high-quality model: some of the photographs may need to be manually calibrated to the other photographs, or the resulting model may need to be edited. The amount of post-processing required varies from project to project, but usually the more complex a scene or object, the more post-processing is required.
Once the model is at an acceptable quality, or it is as good as it could possibly get, there are many options to output the model:
- Dense Point Cloud – The fundamental result of the photogrammetry process is a dense point cloud. The dense point cloud can be exported from the software in many formats: las, laz, ply, xyz and dxf. These file formats can be imported or converted to be used in GIS or CAD software.
- 3-D Textured Mesh – The software (or third party software) can use the dense point cloud to create a 3-D textured mesh. The 3-D textured mesh consist of many (millions) of tiny triangles used to fill the spaces between the points of the dense point cloud. The 3-D textured mesh can be output in ply, fbx, dxf or obj file format, which can be imported into GIS, CAD or mesh software (3-D printing).
- Orthomosaic – If a project contains a landscape, a high-resolution, orthomosaic aerial photograph can be created. The software can digitally combine many aerial photographs to create one seamless, high-resolution image that can be exported as a GeoTiff file.
- Digital Surface Model (DSM) – If the project contains a landscape, the dense point cloud can be converted into a DSM, which can be imported into GIS or CAD software and processed into a Digital Elevation Model (DEM).
- Still Images and Videos – The dense point cloud and 3-D textured mesh can be viewed as still images or videos. This is the least functional use of the models, but they are the most visually appealing representation of the models (especially the videos) and the best option for public viewing and sharing of the models.
Given the high resolution imagery of the models, the most basic use of the models would be site assessment. The models could be used to assess the current condition of a building, structure or landscape, and aid in the decisions of project planning or maintenance. In addition, the models can be used as a comparison to document future changes in conditions as a site changes over time. Once an accurate model is created, the photogrammetry software can measure lengths and volumes based on the model, which can help with documentation and project planning. A more involved use of the models would be to import them into GIS or CAD software to combine them with other data sets, or even to import them into mesh software for the purpose of 3-D printing.
A simple but effective us of the models would fall into advertising. Videos of the models or even interactive 3-D renderings of the models can be uploaded to websites or social media pages, providing a great representation of a site’s appearance and character.
Photogrammetry provides an accurate, cost-effective solution for documenting and planning of complex projects. The technology of digital cameras, drones and software has reached a point that photogrammetry should be considered on all historic and archaeological projects not only for current use, but for posterity.