Viva Series, TPS Functions 681
33.2 Prism Search Methods
33.2.1 Automatic aiming
Description Automatic aiming is the function which recognises and measures the position of a prism
using a CCD array. A laser beam is transmitted and the reflected beam is received by the
built-in CCD array. The position of the reflected spot with respect to the centre of the CCD
is computed. These automatic aiming offsets are used to correct the horizontal and vertical
angles. The automatic aiming offsets are also used to control the motors which turn the
instrument to centre the crosshairs to the prism. In order to minimise the time for meas-
uring, the crosshairs are not moved to the exact centre of the prism. The automatic aiming
offset can be up to 500 cc depending on selected Measure mode. The automatic aiming
function measures the offsets between the crosshairs and prism centre and corrects the
horizontal and vertical angles accordingly. Therefore the horizontal and vertical angles are
measured to the prism-centre, even if the crosshairs are not aimed precisely at the centre
of the prism.
Motorised instruments can be equipped with automatic aiming. For Target aiming: Auto-
matic the instrument can find a static prism and measure a distance once Meas or Dist is
pressed. The instrument does not follow a moving prism.
Field of view The telescope field of view is the region seen when looking through the telescope. The auto-
matic aiming field of view is the region seen by the automatic aiming. Both are identical on
TPS instruments.
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