STEPHEN KAY: Well, on the Portus project, we use total stations for our excavation. On excavation, you can use it for a range of processes. In particular, we use it to record walls, to record levels, location of special finds, location of environmental finds. All of this information is recorded within the total station within the coordinate system. This will give us an accurate location both in the easting and the northing as well as in the height. All of this information can then be passed through other programmes, such as AutoCad or ArcGIS, which we can then feed into the ARK database, which we use on the project.
This will then give us a complete view and a complete spatial database of all the information, which we’re recording on site. Around the site of Portus, we have a number of fixed, known GPS points, which we can then tie in all of our information. The project we use the GPS for a number of different processes, in particular for doing topographical survey, to cover large areas, such as the two area hectare of the Palazzo Imperiale, to provide a deep, detailed topographic model of the area. We also use it to record the location of environmental samples of deep cores, which we’ve taken elsewhere within the hinterland of the project.
I hope that’s given you an impression of the range of different types of surveying that we use on Portus to begin to understand the site.
The Total Station is an electronic theodolite integrated with an electronic distance meter (EDM) to read distances from the instrument to a particular point. Coordinates of an unknown point relative to a known coordinate can be determined using the Total Station as long as a direct line of sight can be established between the two points. Angles and distances are measured from the Total Station to points under survey, and the coordinates (easting, northing and elevation) of surveyed points relative to the Total Station position are calculated using trigonometry and triangulation. To determine an absolute location a Total Station requires line of sight observations and must be set up over a known point or with line of sight to two or more points with known location.
Standing buildings generally expose more than one side so recording needs to accommodate this. Recording will always include a plan of the top of the wall. This indicates the construction of the wall as it will usually show the facing type and any rubble core. Where possible this is drawn on site but in the case of a high up standing wall, this is done from aerial photos or sometimes via our Gigapan robotic camera.
In addition to the top of the wall, usually at least one side of the wall will be recorded as if it is a section. This is used to show the type of construction of the wall, state of preservation and any traces of earlier walls, foundations, constructions methods and so on.
Vertical walls need to have the direction of the walls noted – usually referred to as faces. Faces can be referred to with their direction and internal/external (if known) e.g. south internal, or more usually, you can use the direction in which the wall faces e.g. north-facing. This can be the same as south internal, but is more precise if you do not know if the wall is internal or external. As with all recording, context numbers are really important and need to be assigned to everything. As with sections, we make sure that we have at least two 3D surveyed reference points on our drawings.
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