forum: Benefits of 3D Scanning in Archaeological Excavation
I am beginning to investigate the potential benefits of using a 3D laser scanning system over a survey transit or total station in the area of archaeological excavation. What benefits or hinderances has anyone here confronted when using this type of data capture.
My background is in traditional surveying, topos, boundaries, etc. I'm not familiar with what archaeologist are documenting when they are using traditional instrumentation on archaelogical excavations. What kind of output are they looking for, P,X,Y,Z,Desc? If so, what do they do with it then? Are they simply looking for a topographic map of the site? Any input would be appreciated, especially if you have any photos depicting how the scanner/total station is used on site and what the data output was.
Thanks!
Re: benefits of scanning excavations
Hi D_Drake
As you might expect, there is no straightforward answer to your question! Archaeologists survey on excavations for a wide range of purposes- for everything from providing levels and creating maps up to building integrated databases for use in GIS. Using good total stations and newer dataloggers it is now possible to carry out a lot of the recording of an archaeolgocial excavation digitally and link the resulting database to interpreted survey- this is one of the most important contributions of digital survey to archaeological excavation.
This is where things get tricky for scanning excavations. Laser scanners are a superb way of recording in 3D- somthing which is not easy to do in any uselful level of detail with a total station. However, scanners do not provide any interpretation of the deposits or objects they scan, and so their use on an excavation has to be strictly within a considered strategy for incorporating the interpretation of the site. For example- it would be easy to scan a trench excavating a section through rubble and intermixed soil deposits, but the interpretation of that section has to be carried out in the field, and it is difficult to derive it reliably from the scan data after the event. For this reason you are best to integrate total station survey using shared control.
Other more general limitations with scanning excavations include issues surrounding the resolution required to record a useful level of detail: this can mean that scanning is time consuming, and no one can work in a trench being scanned. Having said all of this, there is still no better way to record a complex site in 3D and some of the experiments that have been carried out have produced great results. Scanning will allow you to revisit any complex stratigraphy and redraw cross sections, calculate volumes, etc that is otherwise very difficult. The only thing to remember is that you need to think carefully about the strategy for interpreting and using the data before starting.
Hope this is useful to you.
Graeme
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Dr Graeme Cavers
Research Associate
University of Nottingham / AOC Archaeology
3D Recording of Excavations Using Terrestrial Laser Scanning
In the Discovery Programme we have been using Terrestrial Laser Scanning (TLS) to record our excavations for the past two years. Traditionally excavations plans would be drawn using frames, however this is slow, its accuracy highly dependant upon the recorders ability, and the result highly subjective. As you only have one bite at recording the excavation “cherry” the traditional method is flawed. The system we have adopted removes the element of the metric measurement from the archaeologist’s hands and into the surveyors. The surveyor, using a rigid fixed control framework for the duration of the excavation (we use plumbers ball cocks on poles), is able to scan areas the archaeologists would normally plan i.e. surfaces and sections. The scans once merged and cleaned are converted to orthoimages for the required areas and then handed over to the archaeologists for their interpretation to be added. This can either be low tech i.e. laminated scans or high tech using tablet PCs & integrated GIS. We went for the former due to costs and we didn’t want to burden the archaeologists with a technology they were not totally used to. We have experimented modelling the excavation up using Geomagic a 3D engineering package, however, time constraints have not allowed us to progress this avenue any further at present.
From our experiences here are the positives and negatives:
POSITIVES
Extremely fast (normal scanning time per context surface @ 5mm res. = 2 hrs, processing 45 mins.)
Removes subjective recording from the primary record
Complex 3D structural elements are easily recorded, especially good at recording building and structural remains
The excavation surfaces can be virtually reconstructed in the post process stage to aid interpretation
NEGATIVES
Expensive technology
Some archaeologists think the scanning completely replaces their recording methodology and don’t spend sufficient time detailing the interpretive aspects. The scanning is only the start of a complete recording and interpretation process.
Deep excavation trenches can cause problems when scanning (probably dependant upon scanner model)
The imaging aspect of scanners is too course
Scanners do not record the subtle changes in soil texture that often form the main evidence of occupation.
The ideal product of the scan a true 3D GIS model is still far from obtainable with the restrictions of the current software technologies.
In 2007 we supplemented the recording process using the Topcon PI-3000 photogrammetry system. By using calibrated fixed lens digital camera suspended beneath a helium balloon/kite system we could capture our own aerial imagery of the excavation surface and create orthimages using digital photogrammetry techniques. This technology was also applied when recording the metric imagery for the sections.