Want this question answered?
it is line set out by the optical axis of the instrument ( level). so it is just an imaginary line that describes the ray of light that allowes us to read different values from the leveling staff. this term arose from the fact that in differential leveling in surveying we must construct horizontal line of sight, but due to collimation error the collimation line (i.e. line of sight) will not be 100% horizontal (by horizontal we mean tangent the level surface at the instrument position), instead it will be slightly deviated. so what we are looking to achieve when we eliminate the collimation error (using the 2 peg test) is a horizontal line of collimation.
Transit and non-transit theodolite.
A theodolite is used to measure angles of a plane. This can be both vertical or horizontal, and it is used with high precision.
20 degree
upper clamb
Is error comes when the line of sight does not coincide with the optical axis of theodolite.
Collimation Error: Collimation error occurs when the collimation axis is not truly horizontal when the instrument is level. The effect is illustrated in the sketch below, where the collimation axis is tilted with respect to the horizontal by an angle α: Figure ( ) In this particular example, the effect is to read too high on the staff. For a typical collimation error of 20", over a sight length of 50m the effect is 5mm. If the sight lengths for back sight and foresight are equal, the linear effect is the same for both readings. When the height difference is calculated, this effect cancels: δh = (b + s. α) - (f + s. α) = b - f That is, the effect of the collimation error is eliminated if sight lengths are kept equal.
Half of the difference between the two positions is called the "index error".
is to eliminate collimation error
error in alignment between the optical axis of a telescope & the declination. it is line set out by the optical axis of the instrument ( level). so it is just an imaginary line that describes the ray of light that allows us to read different values from the leveling staff. this term arose from the fact that in differential leveling in surveying we must construct horizontal line of sight, but due to collimation error the collimation line (i.e. line of sight) will not be 100% horizontal (by horizontal we mean tangent the level surface at the instrument position), instead it will be slightly deviated. so what we are looking to achieve when we eliminate the collimation error (using the 2 peg test) is a horizontal line of collimation.
To check vertical deviation of tower using theodolite, measure the distance between the target and the point of burst in the plane. There must be a normal line of position along a line perpendicular to the lateral deviation.
To operate a Theodolite, first drive a surveyor's nail into the ground where Theodolite will be set up. Second, set up tripod legs and gently place the instrument on the mounting plate then screw in the mounting knob beneath the instrument. Finally, adjust the vertical plummet of the Theodolite.
it is line set out by the optical axis of the instrument ( level). so it is just an imaginary line that describes the ray of light that allowes us to read different values from the leveling staff. this term arose from the fact that in differential leveling in surveying we must construct horizontal line of sight, but due to collimation error the collimation line (i.e. line of sight) will not be 100% horizontal (by horizontal we mean tangent the level surface at the instrument position), instead it will be slightly deviated. so what we are looking to achieve when we eliminate the collimation error (using the 2 peg test) is a horizontal line of collimation.
co adjust error
*find a theodolite or total station *check for collimation *check theodolite vertical axis *set up the theodolite a distance away from the foot of the tower, or closer but using a diagonal eye piece *use left face to bisect bottom point and clamp the horizontal plate *check the tower zenith transit and use the right face to bisect the bottom point and do as explained above *dont forget to record readings of every stage.
there are few types of errors in levelling...... these arr...... 1- instrumental error 2- collimation error 3- errors due to curvature and refraction 4- some other errors also
Father of Theodolite