|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.
|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.