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ABSTRACT
The article evaluates the usability of Leica AT401 laser tracker for long range outdoor measurement.
Firstly, a user-programmed application called ATControl was developed in order to gain a major control of the instrument. Secondly, laboratory testing of Leica AT401 has been performed at the Research Institute of Geodesy, Topography and Cartography (RIGTC). And finally, a repeated outdoor measurement with the laser tracker took place at the Czech State Long Distances Measuring Standard Koštice and the National Calibration Baseline Hvězda.
Even if the instrument is rather designed for industrial metrology rather that for outdoor geodesy, it proofed to be functional under favorable atmospheric conditions. However, the stated 160-m-range is not a parameter on which the measurer could rely and many factors concerning the maximum range has to be taken into account.
EURAMET's research project "Absolute Long Distance Measurement in Air" describes needs for development in this field. Employing laser tracker instruments is one of the new but conventional ways how to increase the accuracy of the distance measurement outdoors and also one of the options how to maintain field length baselines around the world.
Keywords: laser tracker, Leica AT401, long range measurement, laboratory testing, length metrology
INTRODUCTION
Laser trackers as geodetic instruments for measuring horizontal and vertical angles and slope distances are relatively new kind of equipment. As they are not usually designed for classical geodesy, the use of such an instruments usually require some customization which makes sense only in case of special works. Very often, the main purpose of employing laser trackers in geodesy is to increase the accuracy of distance measurement for long distances. Probably the best instrument which fulfils the requirements of surveyors is the laser tracker Leica AT40x (currently AT401 or AT402). Even if this whole article relates to the older Leica AT401 (Fig. 1), most of the findings should be valid for the newer model as well. AT402 underwent a minor hardware updates which do not influence the accuracy and range of distance measurement.
The accuracy (standard deviation) of distance measurement stated by the manufacturer is 5 pm up to 80 m or the same value up to 40 m tested according to ASME B89.4.19-2006 [1]. Typical working volume is noted to be 320 m and therefore 160...