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Distance Between Two
Points
Pacing
Chaining
Temperature
Standardisation
Catenary
Slope
Tension
Tacheometry
Stadia System
Measurement of
Tacheometric Constants
Refraction and Curvature
Theodolite
Tachaeometry
Field Tachaeometry
Electronic Tachaeometry
Field Tacheometry
Tacheometric surveys are usually performed to measure the three dimensional location of points on the landscape so as to produce contour and detail plans for further work, or to produce coordinates for area and volume calculations. Observations are usually performed from known survey stations, often established by traversing. A sample of the field booking sheet is shown below:
|
Station: At A Date: 30/2/90 Party: CO,MS,KR Reference: Job 12/90 Instrument: T2/19 H.I.:1.49 R.l 23.45 Temp:35°C Press:1012mbar |
|||||
| Top | Centre | Lower | Horizontal | Vertical | Description |
| 2.457 | 2.895 | 3.333 | 24° 27' 30" | 272° 45' 00" | Tree 2: 4,8,0.3 |
| 1.873 | 2.145 | 2.416 | 48° 34' 20" | 270° 23' 00" | Fence Corner |
| . . . and so on | |||||
In this example, the vertical angles have been observed by theodolite and therefore have to be coverted to an elevation for use in the formulae as they stand, or the formulae can be modified to accept zenith angles. The first set of readings will be reduced as an example.
| s | = 2.457 - 3.333 = 0.876 | q = +2° 45' 00" |
| S | = 100 s cos 2 q = 100 (0.875) cos2 (2° 45') | |
| = 87.40 metres (8.74) | ||
| RL | = RLA + HI + 100 s cos q sin q - CL | |
| = 23.45 + 1.49 + 100(0.876) cos(2° 45') sin (2° 45') - 2.985 | ||
| = 26.153m (26.15) | ||
One of the most common outputs from a tacheometric survey is a plan of survey showing the features and contours. The procedure for the preparation of these will be discussed in future lectures.
The only other variable necessary to compute the coordinates of the point on which the staff was placed is of course a bearing. This is computed from the horizontal circle reading and a known or adopted reference bearing, similar to the procedure adopted when traversing.