High aim
In geodesy, a high target is a clearly visible surveying or other point which, because of its height, offers an indirect line of sight between distant points.
As a rule, you do not go to the high destination yourself, only measure the direction to it . If this is done from different positions, the coordinates of the high target and thus also new points can be determined. The advantage of the greater range is put into perspective by the refraction , the deviations of which from the normal atmosphere have a greater effect over long distances than short ones.
Common high goals are church towers and high chimneys , high voltage pylons , summit crosses and the like. The best distance to the target depends on the location of the measuring points involved.
A special case are the high photographic goals of astro - or cosmic geodesy , the use of which was successful between 1950 and 1990 in many projects that were supposed to establish connections over long distances. Such high targets are not terrestrial points, but balloon probes , ballistic missiles or artificial earth satellites . In Finland at the end of the 1950s , a distance of 150 km between Turku and Helsinki was measured directly for the first time using precise images of balloons against the starry sky . The method developed by geodesist Yrjö Väisälä was named stellar triangulation because of the use of the star background as a measuring device .