Datum Problem Handling in Local Tie Surveys at Wettzell and Metsähovi

Abstract The datum problem is a fundamental issue in the network adjustment when connecting local measurement to an external reference frame. Datum elements 3D networks are scale, translation, and orientation. We consider here tie at geodetic core stations, where frame latest ITRF realization, ITRF2014, mean epoch of terrestrial observations. Accurate distance measurements used for determination scale. Thus improvement its accuracy inclusion weather account refraction errors essential. For rotation translation network, we need information. Angle observations related coordinate system instrument (e.g. tachymeter) which usually aligned plumb line. Instruments have different vertical orientation every station point direction line does not coincide with normal vector ellipsoid. Horizontally observed set angles oriented arbitrary or approximately directions. External information needed solving absolute points, providing link global system, correction terms (deflection vertical), can be derived from combined terrestrial/GNSS observations, gravity based geoid model, astronomical In this article, present solutions/options framework EMPIR GeoMetre project using example stations Metsähovi Wettzell transformation-free approaches. distant targets promising, since small even millimeter change coordinates significantly affect vector. It shown that both deflection techniques yield same results within error.