Limited accuracy reference free angular position determination

Abstract

Test and calibration of angle measuring instrumentsis an important issue in the areas of geodesy, machineengineering and maintenance, etc. In most of cases,to test or calibrate the instrument a reference device capableof producing the angular values of higher accuracy(comparator) is needed. Other methods of testing and calibration(as cross-calibration or using the same scale as reference)are quite complicated and not always can be implemented.Additionally, in case of testing or calibrationby means of comparison, a precise mechanical adjusting(centering, levelling etc.) of the tested and reference devicesis needed, that kind of adjustment is often very timeconsuming and hard to accomplish. In this paper a veryprinciple of testing and calibration of angle measuring instrumentsby means of digital photogrammetry with limitedaccuracy but without the need of precise adjustingprocedure and with a possibility of the method implementationat industrial facilities is described. In this method theangle of rotation of the calibrated instrument is determinedby means of simple plate attached to the rotary part of instrument,the 3D surface of plate is obtained by photogrammetricmeans, thus the angle between the determinedsurfaces of plate at different angular positions can be determined.Virtual reference angle measure is created insidethe computer software, therefore the method could be describedas the “reference free”. First results of practicalimplementation of the method with the preliminary accuracyevaluations are presented, according to which the accuracyof calibration not exceeding ±2.53´ was reachedduring the initial tests.