4 : Definition of Terms Flashcards
1
Q
- process of determining the difference in elevation between two or more points some distance apart.
- requires a series of set ups of the instrument along a general route and, for each set up, a rod reading back to the point of known elevation and forward to a point of unknown elevation are taken
A
Differential Levelling
2
Q
a fixed point of reference whose elevation is either known or assumed
A
Bench Mark
3
Q
established at intervals throughout the country by the Philippine Coast and Geodetic Surveys (PCGS) or the Bureau of Lands. It consists of bronze or brass disks which are permanently set in concrete foundations. They are marked with the elevation above sea level, the year established, and its reference number.
A
permanent bench marks (PBM)
4
Q
those set up by the surveyor for his own use in a particular surveying project and may have assumed elevations
A
temporary benchmarks (TBM)
5
Q
- a reading taken on a rod held on a point of known or assumed elevation
- referred to as plus sights (+S) as they are added to the elevation of points being sighted to determine the height of instrument
A
Backsight
6
Q
- a reading taken on a rod held on a point whose elevation is to be determined
- referred to as minus sights (-S)
A
Foresight
7
Q
- horizontal distance from the center of the instrument to the rod on which a backsight is taken
A
Backsight Distance (BD)
8
Q
- horizontal distance from the center of the instrument to the rod on which a foresight is taken
A
Foresight Distance (FD)
9
Q
- an intervening point between two bench marks upon which point foresight and backsight rod readings are taken to enable a leveling operation to continue from a new instrument position
- also referred to as change point (CP)
A
Turning Point (TP)
10
Q
- also called height of collimation
- the elevation of the line of sight of an instrument above or below a selected reference datum
A
Height of Instrument
