backsight


Also found in: Dictionary.

backsight

[′bak‚sīt]
(engineering)
A sight on a previously established survey point or line.
Reading a leveling rod in its unchanged position after moving the leveling instrument to a different location.
(navigation)
A marine sextant observation of a celestial body made by facing 180° from the azimuth of the body and using the visible horizon in the direction in which the observer is facing.

backsight

In surveying, a sight on a previously established survey point or line.
References in periodicals archive ?
How to look backward and forward through backsight forethought.
In Figure 1-19, the instrument would be set up at instrument position one (IP1); a backsight would be taken on benchmark one (BM1) and a foresight on the turning point (TP).
In the laser rangefinder interface, backsight and foresight functions were added for enhanced data collection in obstructed situations.
Note that when the instrument is set up halfway between the two stations, Figure 5-9, the error between the rod reading and horizontal is the same in the backsight as in the foresight.
In this illustration, the instrument is much closer to the rod for the backsight than for the foresight.
Height of Instrument--The elevation of the line of sight of a surveying instrument, which is obtained by adding the backsight to the elevation of a known point.
Tenders are invited for Supply of Ic Ramp Backsight (Icr-1253)
The note keeper must remember that the first backsight and the last foresight are also a pair.
In differential leveling, each station is used as a backsight and a foresight.
The backsight is the baseline or the reference line or point that is used as zero angle, as shown in Figure 7-2.
Before stations in an angle and distance topographic survey can be identified, the survey crew must determine what will be used as the backsight for the angles.