Resection (Free Stationing)

In surveying, free stationing (also known as resection) is a method of determining a location of one unknown point in relation to known points. There is a zero point of reference called a Total station. The instrument can be freely positioned so that all survey points are at a suitable sight from the instrument. Setting up the Total station on a known point, often it is not possible to see all survey points. With the Total Station, bearings and distances are measured to at least two known points of a control network. This with a handheld computer recorded data is related to local polar coordinates, defined by the Horizontal Circle of the total station. By a geometric transformation, these polar coordinates are transformed to the coordinate system of the control network. Errors are distributed by least squares adjustment. The position and orientation of the Total Station in relation to where the Control network is established.

Because bearings and distances in a Resection (Free Stationing) are measured, the result may have a different mathematical solution. This method of a "Total station set up" has different names in other languages, e.g. German: (Free Stationing).

Naming is also regulated by the German Institute for Standardization DIN 18 709.

By measuring bearings and distances, local polar coordinates are recorded. The orientation of this local polar coordinate system is defined by the 0° Horizontal Circle of the Total station (polar axis L). The pole of this local polar coordinate system is the Vertical Axis (pole O) of the Total Stations. The polar coordinates (r,f) with the pole are transformed with a Surveying Software in a data collector to the Cartesian coordinates (x,y) of the known points and the coordinates for the position of the Total station are calculated.

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