INTRODUCTION TO TRANSITS AND THEODOLITES
TRANSIT & THEODOLITE
Primary function is the accurate measurement or layout of horizontal and vertical angles.
Determining horizontal and vertical distances by stadia
Extending straight lines
Transits and theodolites operate on the same basic principles
No universally accepted difference between the terms "transit" and "theodolite"
Transits have an open design where the measurements are made by reading verniers on metal circles
Theodolites have a closed design where the measurements are made by reading verniers etched on glass circles
Theodolites are capable of greater precision and accuracy
Parts of a transit
Scales (range from 30" to 10")
Transit verniers (range from 1" to 10')
Compared to transits, theodolites are
more accurate and precise
Transits are more common in the U.S. but are being replaced by theodolites
TYPES OF THEODOLITES
Electrical digital theodolites
This design enables horizontal angles to be repeated any number of times and added directly on the instrument circle.
Advantages of this design are:
better accuracy obtained through averaging
disclosure of errors and mistakes by comparing values of the single and multiple readings
Measure the angle (e.g. 23° 19')
Tighten the lower motion clamp
Re-sight on the initial point
Sight the second point and re-measure the angle (e.g. 46° 40')
Repeat process as many times as desired
Solution equals the average of the measurements, or the final measurement divided by the number of measurements
1st measurement: 23° 19'
2nd measurement: 46° 40'
3rd measurement: 69° 59'
4th measurement: 93° 23'
5th measurement: 116° 44'
6th measurement: 140° 02'
average angle measurement: 23° 20'
Non-repeating instrument that has no lower motion
Reads "directions" rather than angles
Angles are obtained by subtracting the first direction reading from the second direction reading
Set up the theodolite
Sight the initial point and read the direction (e.g. 31° 19'27")
Sight the second point and read the direction (e.g. 85° 24'49")
The angle is then calculated as the difference between the two directions (e.g. 54° 05'22")
ELECTRONIC DIGITAL THEODOLITES
Automatically reads and records horizontal and vertical angles
Eliminates the manual reading of scales on graduated circles
ADVANTAGES OF ELECTRONIC DIGITAL THEODOLITES
Circles can be instantaneously zeroed, or initialized to any value
Angles can be measured with increasing values either left or right
Angles measured by repetition can be added to provide a total larger than 360°
Mistakes in reading angles are greatly reduced
Speed of operation is increased
Cost of instruments is lower
TOTAL STATION INSTRUMENTS
An electronic digital theodolite and an electronic distance measurement instrument in one integral unit
They can automatically record horizontal and vertical angles and slope distances from a single setup
Slope distances can be reduced to horizontal and vertical components instantaneously
Given initial data they will display positions and elevations of sighted points