Knowing exact locations on site – Total Station survey

Richard Anderson surveying at Zagora
Richard Anderson using a Total Station (the green device on the yellow tripod) for surveying at Zagora © PHM; photo by Irma Havlicek
by Irma Havlicek
Powerhouse Museum Online Producer

A Total Station is an electronic/optical device that uses laser signals to determine precise locations (to within about half a centimetre).

In the application at Zagora, it enables the archaeologists to establish a precise frame of reference on the land, and is also being used to confirm the exact location of our test trenches. This means that if any architectural structures or artefacts are located in the trenches, their exact location will be known.

Until the Total Station was developed, surveying was done with theodolites which measured angles only, and three-dimensional surveying was only possible within the very limited range of traditional distance measurement which meant hand measurement with surveying tapes.

A target fixed to a building
One of the reflective targets which enable the position of the Total Station to be determined © PHM; photo by Irma Havlicek
To begin, the Total Station device stands on a tripod at a high point on the land and sends a distance measuring beam (laser or, as in our case, infra-red) onto special reflective material placed at prominent points, known as ‘control points’, that have been very carefully surveyed. The bearings and distances to a minimum of two these points allow the position of the Total Station to be determined.

Once the position of the Total Station has been determined, it is a simple matter to measure the position of anything that can be sighted from that position.

Richard Anderson aiming the laser at the marker held by Andrew Wilson
Richard Anderson aiming the infra-red beam at the prism pole held by Andrew Wilson © PHM; photo by Irma Havlicek

A closer view of the prism pole
A closer view of the prism pole © PHM; photo by Irma Havlicek
A team member then holds a pole with a prism on top of it that allows the bearing and distance to that point to be measured by the Total Station which determines the position of that point. The data is transferred from the Total Station into a computer running CAD software which creates a digital drawing as the survey is in progress.

So, for example, if the Total Station were to send its signal to each corner of a stone making up a stone wall, the CAD software would create a drawing of that stone wall, with the precise location of each stone being recorded.

Total Station surveying has been done at various stages of the Zagora Archaeological Project, and the results of the survey are being relied upon to establish locations throughout the site, and to ensure the precise location of any trenches to be dug and building structures or artefacts that are uncovered during excavation.

The great advantage of the Total Station is the speed and accuracy of determining location. It doesn’t actually do anything a tape measure and a theodolite couldn’t do – but it does it far more easily and accurately.

Andrew Wilson holding the target for Richard Anderson
Andrew Wilson holding the target for Richard Anderson © PHM; photo by Irma Havlicek

In order to understand the way people use the landscape you have to know where all the elements of the site are in relation to other things. It’s about understanding the space that people created and occupied. That’s why you need to know how big rooms are, where walls are, where artefacts are found – to know the relationship between these things.

One of the main reasons why great accuracy is important is so we know as reliably as possible where artefacts were found – because once they are removed, there is no putting them back. So we need to record where they were located with certainty.

Rudy Alagich holding the prism pole in position
Rudy Alagich holding the prism pole in position © PHM; photo by Irma Havlicek
Rudy Alagich holding the prism pole
Rudy Alagich holding the prism pole – he’d be holding it more vertically if Richard was about to send the signal from the Total Station. © PHM; photo by Irma Havlicek

Richard Anderson, Emeritus Architect, Athenian Agora Excavations, has led the Total Station survey team; together with Andrew Wilson and Rudy Alagich, though other team members have also helped on occasion.

Richard Anderson using a 10-year-old tablet to record survey details
Richard Anderson using a veteran tablet computer to record survey details. You don’t actually need the tablet device – but using it, you can see what you are drawing as it is being surveyed. This allows errors to be immediately seen and corrected. For example, if you are surveying stones in a wall, you can see if you have missed one out, or surveyed one twice.
© PHM; photo by Irma Havlicek
One of the original markers
One of the original markers used by J. J. Coulton during the 1960s/70s seasons © PHM; photo by Irma Havlicek
Meg Miller and Richard Anderson preparing to survey
Meg Miller and Richard Anderson preparing to survey using the Total Station (the device on top of the yellow tripod). The data is transferred from the Total Station into the CAD software on the tablet computer Richard is holding © PHM; photo by Irma Havlicek

Andrew Wilson makes use of the field data in a variety of applications. These include ArcGIS, a widely used geographic information system, and Heurist, the University of Sydney’s humanities research database. The GIS can be used to produce basic plans, more complex analyses of the archaeological data and 3D visualisations of the site and its structures.

The Heurist database is used to build and maintain the complex relationships between the artefacts and other evidence from the site, the locations where they were found and the interpretations that team members develop about them, as well as associated publications and comparable examples from other sites.

Heurist screenshot of J15 artefacts
The Heurist database – showing artefacts related to the rooms in the J15 sector of Zagora in which they were found, and on a timeline; Andrew Wilson and Beatrice McLoughlin are the Heurist wizards on the Zagora project © University of Sydney

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