Monday, 27 July 2015

Documentation of a bas-relief on a cliff : the workflow

This summer, between May and June, we worked for a joint mission, led by the University of Innsbruck (Institut für Alte Geschichte und Altorientalistik) and the Cultural Heritage, Handcrafts and Tourism Organization of Iran. The project was held in Firuzabad, in the Pars Province of Iran. We will write more details about this work in the next post. By now I just want to use some material we collected to illustrate the work-flow in data acquiring during an archaeological documentation of a bas-relief on a cliff.
The video below shows the overall process.



You can see the initial preparation phase (1), during which we placed the Ground Control Point (GCP) to perform normal 2D vertical photo-mapping and to rectify and georeference the 3D point-cloud. Than (2) we collected pictures with three different flights of our DIY drone, in order to use them with different open source SfM/MVSR software (PPT, openMVG and MicMac), to reach the best possible result: a couple of flights with parallel camera, to have a good superimposition of the whole bas-relief, and a higher acquisition to cover the upper details. In the meantime (3) another operator (+Rupert Gietl) was collecting pictures from the ground, to register also the lower perspective. Later (4), I prepared the total station and collected the GCP, thanks to some fixed points we placed the day befor (0) with our GPS. Finally +Rupert Gietl  took the last (very close) details photos, using a ladder.
The entire process lasted more or less four hours, but we needed some more time the day before to place the fixed GCP down in the valley (in international Geographic Coordinates System). A good part of the work involved just the logistics or the approach to the site, and has been slowed by the transportation of the necessary equipment (ladder, total station and drone) through a couple of passages where it was necessary to climb some rocks.
It is interesting to note that it would not have been possible to accomplish this mission with a commercial drone, due to the embargo rules (which are currently under revision), while with a DIY hexacopter it has been simple to disassemble the components which were not allowed (like the FPV system ore the GPS controlled flight).
I hope this post was useful, have a nice day!
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