Eastern Geo Services Inc.

Photogrammetry – Light + Drawing + Measurement

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Photogrammetry is science of making measurements from photographs. It is useful to aid in determining positions of objects and topographical feature’s coordinates on the Earth’s surface. To facilitate this process it is necessary to know the scale or geometric relationship between the image and the object being measured at the moment of photographing. This is usually accomplished by taking measurements on the ground (control points) and determining the distance between two or more. With this information you can scale the photographs and begin measurements.

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In aerial photogrammetry a camera is mounted on a UAV and pictures of the Earth’s surface and multiple overlapping pictures are taken along a flight route. The photos are processed with advanced software on a computer, and they can help to produce a digital elevation model or a DEM for short. This type of DEM will be a representation of the tops of objects and terrain features as captured from a photograph. One limitation of aerial photogrammetry is that, while X- and Y-data is captured with high accuracy, Z-data is of poor quality, and specifically the true bare-Earth elevations cannot be captured is cases of tree cover. However, photogrammetry excels at capturing the edges of buildings and objects where other remote sensing applications such as LiDAR does not.

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A typical output of photogrammetry is a map, drawing, measurement or 3D model. The process works by taking multiple images from at least two locations and “triangulating” lines of sight to produce 3D coordinates of a feature of interest. This can be done on the ground in the case of a theodolite mounted on a tripod (terrestrial) or from a UAV with sensitive photogrammetric equipment (aerial).

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Once a product is created with photogrammetry an analysis or a photo interpretation can be performed next. During this process the data collected is used to evaluate, analyze, classify, and interpret the image’s contents. There are two ways to utilise these processes: as interpretive photogrammetry and metric photogrammetry.

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Interpretative Photogrammetry involves recognizing and identifying objects and judging their significance through systematic analysis from photographic images. When used in terrestrial photogrammetry it has particular applications in forestry research, and qualitative analysis. When used in aerial analysis it has particular applications in agriculture, archaeology, geology, and environmental analysis.

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Metric Photogrammetry involves making precise measurements on photographs and other information relative to points of interest. This process results in determination of measurable physical characteristics such as distances, elevations, areas, volumes, slopes, and cross-sections. This is more common in aerial photogrammetry and has particular applications in construction, environmental analysis, engineering industry support, mineral exploration/mining, quarrying, topographic mapping, and petroleum industry support.