Sunday, 31 July 2016

Survey crew: Total Station

The Total Station is a fancy laser machine that tells us where things are in a site.
We use it to map artefacts within a cutting, context topography (what the surface is like in 3D), features, field topography, grid points for GPR and Radiometer, and more.
The machine takes at least two people to run, but the ideal team is three. That way we can communicate easier, and switch out as needed. It also helps out in the fields, where we can have one person mostly warding off the cows, while the other two take points. Phones/comms help when working long-distance, but we also have a simple system of hand-signals to communicate without words.


It consists of three parts: a tripod, which has to be set up perfectly level; the machine itself (we currently use Leica brand), which contains the computer, laser, and recording bits; and the standing rod, which is basically a spear with a fancy mirror (prism) on the not-pointy end.

To set up the total station. you also need Datums, or fixed points, to use as permanent references. They must be constant across years, so that data taken throughout the 10-year project is consistent and compatible.
To create a Datum, we find a good spot, dig a small hole, fill it with concrete, label it carefully before it dries, and record its exact location in the computer program after it dries.
We also create Temporary Datums, to be used for just one year, by pounding a stake into the ground. Their coordinates can be replaced in the computer each year.

Setup itself means finding a Datum, setting up the tripod so that it is centered on the datum and completely level, and attaching the machine to it. Since the data we collect is 3D, it is extremely important that it is level. if it wasn't, all the points on one side of the machine would be recorded as higher or lower than the actual physical points are, which could seriously mess up the mapping and interpretation.
Once that is done, we tell the machine which Datum it is on and how tall the tripod is, then we point it at another Datum and orient it. If this is done correctly, the machine knows where North is.
Then we tell it how tall the standing rod is (usually we keep it at its shortest setting, 1.3 meters, but if we are in a deep excavation, or behind hills, trees, or other obstacles, we may need to raise it to maintain the laser sightline), so it knows exactly where the point on the ground is, even though it can't see the ground.

Taking a point is fairly simple. Get the computer to the correct project and survey screen, hold the standing rod so that it is straight up-and-down level and steady with the mirror facing the machine, line up the laser sights with the mirror, and click to shoot. Then signal the person holding the rod to move to the next point, and repeat.

Once we have all the data from one location, we take it down and set up somewhere else, or take the machine to the Office and upload all the information to the computers to be manipulated into maps and other useful graphics.

My experience this year

After showing some interest in several parts of the project, I ended up sticking with Total Station because I learned the system fairly quickly (although there isn't a manual that we know of, so we still learn new things as we go), and enjoyed the work and the team. Also LASERS!

Working the Station is tricky enough to require skill, but simple enough that you're not constantly lost. Good communication with the team is important to make the work go smoothly, so smaller group sizes work better, especially when we all get along. The other two on Total Station are Dave and Colin, who are both pretty chill. We all seemed to agree on the background music, too, which helped everyone enjoy themselves.

We hike around a lot, lugging the box and pointy things, which is great for impromptu weight training on the way to the next assignment. :)
When using the machine... we press the Left button a lot. The system isn't totally efficient, and sometimes it takes ten or more button presses to get between taking a point and reviewing the point (like when we're re-setting stakes to specific coordinates, or going back to find the last artefact number we shot).
Once you get the hang of it though, it's more amusing than frustrating. And if you're careful, you don't have to review the points very often, either.

Another benefit to the Total Station is that you are needed at all the field sites, so you get to see what's going on everywhere but the lab.
Most people at the dig are more or less confined to their one specialized zone, which is good because they know a lot about it and can interpret it better than others, but also means they don't know very much about what's going on with the other teams.
We got to see whenever a cutting found a new context, artefact, or feature, what parts of the field were getting zapped with GPR or Radiometer, and even what the data looked like in the Office, while it was being manipulated; all the while collecting our own important information, finishing other projects, and setting up new sites and Datums in preparation for next year.

If I manage to come back next year, I might well be on this team again. I enjoyed it.
-Rozlyn MacDermott

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