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!

OpenJUMP: query to extract single points from a general vector layer

Hi all,

today I am working on data elaboration of an archaeological excavation. I decided to record a short videotutorial to show how to perform a very simple query in OpenJUMP (which is a topic I am often asked to explain during lessons about archeology and open source). Before to start, I'll write a short introduction regarding the processing of this data, just to understand why I need to perform this kind of query. 

I worked on this excavations collecting all the data in a local system (with simple 3D Cartesian coordinates), because the job was an emergency archeology project and I did not have the time to set up a geographic coordinate system on the field, before the construction site began. Just at the and of the excavation, I could come with a RTK GPS, to collect some Ground Control Points (GCP) in UTM WGS84. This is the reason why in this time, when I am processing the data, I had to put together all the daily total station downloads in a single cvs file, which I georeferenced in OpenJUMP, using the GCP I collected with the GPS. The problem is that now I will have to separate again the single points, grouping them according to their function (e.g. points for photomapping of area 1, height points of the same area, points for SfM georeferencing, find-points and so on...). To do this operation, I will simply use OpenJUMp (where I loaded and georeferenced the csv file), performing a query on the attribute (the name) of cumulative vector layer , which will tell me where are the the points I need. In this way I can select in the GIS the features I am looking for and put them in a new vector level, copying the db schema of the cumulative layer (name, y, x, z, code). At the end of the process, I will have single separated vector files which I will use in the next steps of data processing (photomapping, 3D, ecc...).

Here is the videotutorial I uploaded in the ArcheOS tutorila wiki (rom Insbruck University):

I hope it was useful, have a nice day!

Extreme SfM: precarious situations and workplace safety

This post is a further contribution regarding the main benefit of SfM: its versatility. 

Thanks to its speed during the phase of data acquisition, this technique allows us to intervene quickly in the case where the archaeological excavation exposes precarious situations, often related with collapsing structures.

The image below is good example: we were working in the vicinity of a church, checking the excavator. The left pictures shows the part of a wall which was exposed during this operation, while the right photo reports the same subject just twenty minutes later.

The wall befor and after the collapse

Luckily, seen the precaurious conditions of the structure, we decided to document it with SfM and IBM techniques, and this is the 3D restitution of the wall before the collapse.

The 3D model of the wall

However, the documentation of archaeological arthefacts before their destruction, is just one of the benefits of SfM (mainly related with the speed during data acquisition). In fact the versatility of this technique is strongly connected with the hardware we need to collect the data: a simple digital camera. This make it possible to work without the necessity of a direct contact with object to be documented (especially if we can support the excavation with a direct reflex total station, to record the Ground Control Points needed in the post-processing georeferencing operations). This way to operate lead to minimize the risk and increase the safety in the workplace. The images below regard an example of this situation: sometimes it happen to be called to evaluate the damnages of costruction sites, already underway without the archaeological control. In these cases it can happen to document precarious situation, but, using SfM techniques, there is no need to stand in risky places (like under a section with many gravel layers), because all the operations can be done from a safety distance.

The gravel section

The 3D puincloud (thin points)

The 3D pointcloud (thik points)

 I hope this post was useful, have a nice day!