APAC    Photogrammetry

Photogrammetry
Photogrammetry is a technique whereby measurements can be taken from photographs where known scales are included. Photogrammetry as a technique is not new and has been used for many years, however, Digital Photogrammetry differs is the efficiency of data collection, the nature of the processing plus the quality, and accuracy of the results.

The data produced with the Topcon system used by A.P.A.C. Ltd, provides a 3 dimensional photograph of the object surveyed, allowing for inspection in virtual space. The image produced is fully interactive and can be questioned for measurements in three dimensional space including area, surface area and volume.

The full implications of this technique are only just being understood but its obvious ability to produce as close to a total record as possible will at some time make it a prime requirement in archaeology.

The efficiency of the system is extremely cost effective in comparison to other time and manpower dependent techniques. A minimum of two photographs can produce effective results dependent on the nature of the subject being recorded.

Uses of this technique are suited to a variety of needs: architectural survey and recording excavation recording and artefact recording. Its implementation can be extremely useful in producing an archive.

Digital Photogrammetry
This technique allows for accurate recording of features or structures to an incredible level of detail. The information produced results in a total record of the subject surveyed, that can be interrogated to produce 3D measurement including volume and area.
ISO example (click for larger image)

The process can be used to produce photo-realistic virtual modelling with applications such as "walkthroughs".

The technique lends it self a multitude of applications from building recording, to detailed artefact research. Output can be made direct to Cad or illustration packages.

The simple process involves taking a pair of photographs, (stereo pair), of an object from two calculated positions. The stereo pair is then orientated and set to real coordinates to produce a 3D digital terrain model.
Wall (click for larger image)

The model is then contoured and textured to produce a 3D photograph which can be manipulated in Virtual 3D space. Any measurement can then be taken directly from the photograph. A.P.A.C. Ltd is currently working with Site Scan, on a management plan to record 2.5 acres of medieval stone wall, ranging from 3 to 10 metres high. The photogrammetry results will be converted to digital drawings to facilitate the accurate rebuilding of sections of wall; on a stone by stone basis, in the event of future collapses.
Wall Grid (click for larger image)

The data produced can be used to obtain accurate measurements in height, width and depth. This technique can be easily applied to most historic building reconstruction/development. The data produced can be used to obtain accurate measurements in height, width and depth. Invaluable for applications such as: detailed desktop research, reconstruction, conservation, or even leisure and tourism.

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