## INTRODUCTION TO TRANSITS AND THEODOLITES

### TRANSIT & THEODOLITE

• Primary function is the accurate measurement or layout of horizontal and vertical angles.
• Other functions
Determining horizontal and vertical distances by stadia
Extending straight lines
Differential leveling

### DEFINITIONS

• Transits and theodolites operate on the same basic principles
• No universally accepted difference between the terms "transit" and "theodolite"
• Distinguishing characteristics:
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

### TRANSITS

Parts of a transit
Upper Plate
Lower Plate
Scales (range from 30" to 10")
Transit verniers (range from 1" to 10')

### THEODOLITES

Compared to transits, theodolites are
compact
lightweight
more accurate and precise

Transits are more common in the U.S. but are being replaced by theodolites

### TYPES OF THEODOLITES

• Repeating theodolites
• Directional theodolites
• Electrical digital theodolites
• Total stations

### REPEATING 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

### REPEATING MEASUREMENTS

• 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

### REPEATING 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'

### DIRECTIONAL THEODOLITES

• 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

### DIRECTIONAL MEASUREMENTS

• 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

### 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