Tachymetry |
Tachymetry is used for larger objects or when photogrammetry is not suitable for the situation (see here for a comparison of both methods). Alike photogrammetry the tachymetric survey can be done statically (so with the object on Terra Firma) and dynamically (with the object afloat), without loss of accuracy.
In order to ensure maximum quality all sensors and base points are measured from at least two stations and processed using a least squares network adjustment.
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 | Accuracy-wise there is little difference between photogrammetry and tachymetry. Both methods supplement each other perfectly and can even be used together on the same project.
The expected accuracies (1σ, 68%) are a minimum of 1:10,000 for X,Y and a minimum of 1:15,000 for Z coordinates (assuming that de Z-axis corresponds with the local vertical). For main points (base points, antennae, transducers etc.) this can increase to respectively 1:20,000 and 1:30,000 or better. The accuracy's lower limit (1σ, 68%) is about 0.0005m. This implies that with an object of 100 metres an X,Y accuracy can be expected of 0.005 metres, while the Z accuracy will be 0.003 metres.
Once an object has been measured by Starmountain Survey & Consultancy, any additional points (antennae for instance) can be measured at a later date within an hour without loss of accuracy. These measurements can be done while afloat, reducing down-time considerably. |
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