Abstract: In an electro-optical measuring system which utilizes a sin/cos signal pair to determine the extent and direction of physical displacement, measurement errors often occurring as a result of extraneous DC level shifts in generated signals are corrected in a procedure which regularly samples the maxima and minima of the signals, derives from those values the median DC levels of the signals, compares the median levels to a reference DC level in the system to determine any differences, and applies any detected differences as corrective factors to position measurement signal values.

Abstract: The surveying system comprises a theodolite which provides digital data from electro-optical horizontal and vertical circle reading components and includes a level sensor which generates digital data relative to the attitude of the vertical axis of the instrument. Additional means are included for presetting instrument correction and scaling factors which together with angle and level data are processed by an on-board microcomputer to yield accurate digital displays of horizontal and vertical angles. Provision is also made for the input of digital slope range data from an electronic distance measuring instrument to be displayed directly or processed with horizontal and vertical angle data by the microcomputer to provide vector coordinates of the observed target. In response to operator selection from parameter and vector functions the control program cycles the processing of relevant data in order to provide a repeatedly updated display of any desired function.

Abstract: The surveying system comprises a theodolite which provides digital data from electro-optical horizontal and vertical circle reading components and includes a level sensor which generates digital data relative to the attitude of the vertical axis of the instrument. Additional means are included for presetting instrument correction and scaling factors which together with angle and level data are processed by an on-board microcomputer to yield accurate digital displays of horizontal and vertical angles. Provision is also made for the input of digital slope range data from an electronic distance measuring instrument to be displayed directly or processed with horizontal and vertical angle data by the microcomputer to provide vector coordinates of the observed target. In response to operator selection from parameter and vector functions the control program cycles the processing of relevant data in order to provide a repeatedly updated display of any desired function.