Basic Surveying Tasks How-To With a Total Station

By accentu8

Total stations are used wherever the positions of points or both positions and heights need to be determined. A total station consists of a theodolite with a built-in distance meter and can simultaneously measure angles and distances. Here are four basic tasks you will likely be called upon to perform with your total station.


1. Extrapolating a Straight Line

1) Position the instrument at point B.
2) Target point A, transit the telescope (i.e., reverse it) and mark point C1.
3) Turn the instrument 200 gon (180°) and target point A again.
4) Transit the telescope again and mark point C2. Point C, the mid-point between C1 and C2, corresponds exactly to the extrapolation of the line AB.
Extrapolating a straight line with a total station.Extrapolating a straight line with a total station.

A line-of-sight error is responsible for the discrepancy between C1 and C2. Where the line of sight is inclined, the influence of the errors is a combination of target error, tilting-axis error, and vertical-axis error.

2. Polar Stakeout of a Point

1) Set up the instrument at point A and target point B.
2) Set the horizontal circle to zero (refer to the user manual).
3) Rotate the instrument until α appears in the display.
4) Guide the reflector carrier (person) into and along the line of sight of the telescope, continually measuring the horizontal distance until point P is reached.
Polar stake-out of a point with a total station.Polar stakeout of a point with a total station.

The setting-out elements (angle and distance) here relate to a known point A and to a known starting direction from A to B.

3. Measuring Slopes

1) Place the instrument on a point along the straight line, the slope of which is to be determined, and position a reflector pole at a second point along that line.
2) Enter the instrument height i and the target height t (prism). The vertical angle    reading in gon or degrees can be set to % (refer to the user manual for your total station model) so that the slope can be read off directly in %.
3) Target the center of the prism and measure the distance. The slope is shown on the display in %.
Measuring slopes with a total station.Measuring slopes with a total station.

4. Plumbing Up or Down

Plumbing down from a height point, plumbing up from a ground point, and inspecting a vertical line on a structure can be carried out accurately in just one telescope face, but only if the telescope describes a precisely vertical plane when it is moved up and down. To make sure this occurs, proceed as follows:

1) Target a high point A, then tilt the telescope down and mark the ground point B.
2) Transit the telescope and repeat step 1 in the second face. Mark point C.
3) The mid-point between B and C is the exact plumbing point.
Plumbing up or down with a total station.Plumbing up or down with a total station.

If these two points do not coincide, you may have encountered a tilting-axis error and/or an inclined vertical axis. To minimize the influence of vertical-axis tilt on steep sites, be sure to level your total station precisely before beginning your work.

Article taken from the Blackboard Allen Precision Instrumnets sight

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