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Which of the following cannot be done with the help of non-transit theodolite?
Back sighting
Face left to Face right
Transiting
All of the above
All of the above
A non-transit theodolite is a simplified type of theodolite where the telescope cannot be revolved 180 degrees in a vertical plane. Consequently, it is incapable of performing 'transiting' (plunging), changing 'face' (face left to face right), or taking accurate back-sights through rotation of the telescope across the horizontal axis.
A non-transit theodolite is a simplified type of theodolite where the telescope cannot be revolved 180 degrees in a vertical plane. Consequently, it is incapable of performing 'transiting' (plunging), changing 'face' (face left to face right), or taking accurate back-sights through rotation of the telescope across the horizontal axis.
The design of a non-transit theodolite restricts the telescope to vertical rotation only within a limited range. Because the telescope cannot be rotated around its horizontal axis (the trunnion axis), the vertical circle cannot be inverted, preventing the standard procedure of face change to eliminate instrumental errors.
The primary distinction between transit and non-transit theodolites is the capability to rotate the telescope 180° in the vertical plane.
Transiting is the process of turning the telescope 180° in the vertical circle, which is the defining feature of a Transit theodolite.
Non-transit theodolites are largely obsolete in modern surveying due to their inability to eliminate collimation errors via face changes.
Lighter in weight compared to transit theodolites
Mechanically simpler design
Cannot eliminate systematic errors by face change
Limited field applications compared to transit theodolites
Incapable of direct vertical angle measurement over full range
Basic surveying educational demonstrations
Limited horizontal angle measurement tasks
| Feature | Non-Transit | Transit |
|---|---|---|
Vertical Rotation | Restricted (< 180°) | Full (360°) |
Face Change | Not Possible | Possible |
The term 'transit' refers to the action of rotating the telescope 180 degrees around its horizontal trunnion axis.
Option A (Back sighting) is typically performed by rotating the theodolite in the horizontal plane, but for non-transit theodolites, the lack of face-reversal prevents the standard elimination of observational error in sighting.
D is correct — A non-transit theodolite lacks the mechanical provision to rotate the telescope 180 degrees vertically, making transiting, face changing, and precise back-sighting impossible.
Always remember that the word 'transit' in surveying refers specifically to the capability of plunging the telescope to eliminate instrumental errors.