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Surveying -
leveling,
| Question | Answer |
|---|---|
| reason for leveling | the measurement process to determine height hight on maps ensures construction at correct gradient enables horizontal distance to be calaculate |
| principles of leveling | uesd to measuer the difference in height between two points if the hight of one point is known the the hight of another can be determined |
| level line | one that is at a constant height- realitive to the mean sea level and because it follows the mean surface it must be curved itself |
| Datum | a level line is chosen to which the elevation of all points are related in the uk chosen datum is msl at newlyn cornwall |
| Horizontal line | line tangential to the level line at any particular point. it is perpendicular to the direction of gravity at any point |
| line of colimation | the line of site of the instrument |
| reduced level | height of a point realitive to the chosen datum |
| Benchmarks | reference marks or points, the reduced level of which have been accurately determined by levelling |
| Ordnance Bench Marks (OBM) | established on Ordnance from datum at Newlyn, Cornwall |
| Temporary Bench Marks | set up on stable points near construction sites where no OBM is found |
| collimation error | due to the line of sight not being horizontal |
| instrument set up midway between two points | due to curvature of the earth |
Created by:
anthonyokereke
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