3D positioning technology

The RTS series total station uses a combination of precise angle measurement technology in the horizontal and vertical planes and precise distance measurement capability to establish the 3D position of a target location. The distance measurement system can either use a prism located at the point to be measured, or its DR reflectorless measurement capability to measure from any surface in the line of sight of the telescope.

The principles of angle measurement are based on reading an integrated signal over two opposite areas of the angle sensor and producing a mean angular value. This eliminates inaccuracies caused by conventional circle eccentricity and graduation.

In addition, the angle measurement system compensates for the following automatic corrections:

  • Instrument mislevelment (deviation of the plumb axis).

  • Horizontal and vertical collimation error.

  • Trunnion axis tilt.

Correction for mislevelment

The RTS series total station automatically corrects for mislevelments up to ±6 ’. The instrument warns the operator immediately of any mislevelments in excess of ±6 ’(±0.11 grads).

The RTS series total station also utilizes SurePoint to automatically correct the pointing of the telescope for all mislevelment and trunnion axis errors in real time during operation.

Trimble Construction field software operating on a Trimble controller computes and applies the corrections for all of these errors in all 3D positions generated by the instrument.

Correction for collimation errors

The horizontal collimation error is the deviation of the sighting axis from its required position at right angles to trunnion axis.

The vertical collimation error is the difference between the vertical circle zero and the plumb axis of the instrument.

Traditionally, collimation errors were eliminated by observing angles in both instrument faces. In the RTS series total station, a pre-measurement collimation test is performed to determine the collimation errors. Angular measurements are observed in both instrument faces, the collimation errors are calculated, and the respective correction values are stored in the instrument. The collimation correction values are then applied to all subsequent angle measurements that are used to generate 3D point positions with the instrument. Measurements made in a single face are corrected for collimation errors, which eliminates the need to measure in both instrument faces.

Carry out a collimation test in the following situations:

  • Whenever the instrument may have been roughly handled during transport.

  • When the ambient temperature differs by more than 10 °C (18 °F) from the previous collimation test.

  • Immediately prior to high precision angle measurements in one face.

RTS series total station with Autolock

A RTS series total station with Autolock can automatically lock and track a prism target.

Pointing errors caused by slight misalignment of the instruments tracker have a similar effect to the HA and VA Collimation errors detailed above.

To correct for the tracker collimation errors, carry out a tracker collimation test. The tracker collimation test automatically observes angular measurements to a target in both faces, the tracker collimation errors are calculated and the respective correction values are stored in the instrument. The tracker collimation correction values are then applied to all subsequent position measurements observed when Autolock is enabled. Angles observed in a single face are corrected for collimation errors, which removes the need to measure in both instrument faces.

Carry out a tracker collimation test in the following situations:

  • Whenever the instrument may have been roughly handled during transport.

  • When the ambient temperature differs by more than 10 °C (18 °F) from the previous collimation test.

  • Immediately prior to high precision angle measurements using Autolock in a single face.

Correction for trunnion axis tilt

The trunnion axis tilt error is the deviation of the trunnion axis of the telescope from its required position at right angles to the plumb axis of the instrument.

 

In the RTS series total station instrument, perform a pre-measurement trunnion axis tilt test to determine the trunnion axis tilt error. Angular measurements are observed in both instrument faces, the trunnion axis tilt error is calculated, and the respective correction value is stored in the instrument. The trunnion axis tilt correction value is then applied to all measured positions via a correction to the horizontal angle value and an automatic repointing of the telescope using SurePoint technology.

Carry out a trunnion axis tilt test in the following situations:

  • Whenever the instrument may have been roughly handled during transport.

  • When the ambient temperature differs by more than 10 °C (18 °F) from the previous collimation test.

  • Immediately prior to high precision angle measurements in one face, especially where the vertical angles significantly deviate from the horizontal plane.

Averaging measurements to reduce sighting errors

The RTS series total station instrument automatically reduces sighting errors caused by the misalignment of the instrument to the target or by pole movement during measurement. The following techniques can be used:

  • Use Autolock. When Autolock is enabled, the instrument automatically locks onto and tracks the target. Manual sighting errors are reduced.

  • Automatically average angles during distance measurement. When measuring in Standard mode, the instrument takes approximately 1.2 seconds to measure the distance. Angles returned to the instrument at 1000 Hz, are averaged over the 1.2-second period to obtain an averaged angle measurement. The resultant angle measurement is an average of over 1200 observations.