Steep vision
As Steilvisur the designated surveyor and civil a steep upward or downward inclined sighting of a measuring point . In technical terms, this means elevation and depth angles over about 30 ° ( zenith distance under 60 ° or over 120 °).
Apart from the uncomfortable body position when aiming and reading the theodolite , steep sightings - which are unavoidable in high mountains - have other disadvantages:
- the influence of the tilting axis and standing axis error can reach considerable values; if this influence of the measurement accuracy will keep (the Sekundentheodolit 1-3 " or <1m gon ), you have to both county locations and with good tilt sensor , or tab dragonfly work
- the reduction of the distance measurement to the horizontal distance depends on the measurement accuracy of the elevation angle.
In national surveying , flat sights are therefore preferred, especially in the first-order basic network . If the trigonometric points are on mountains of about the same height, this is also advantageous for the often disturbing air turbulence.
When measuring time and angle for celestial bodies - i.e. in astrometry and geodetic astronomy - naturally steep visions predominate. Particularly precise rider and hanging vials, which are attached directly to the tilting axis, are used here for large special instruments. However, one advantage of steep star visions is that the astronomical refraction hardly deviates from the computational model .