INTRODUCTION TO TRANSITS AND THEODOLITES

TRANSIT & THEODOLITE

  • Primary function is the accurate measurement or layout of horizontal and vertical angles.
  • Other functions

    DEFINITIONS

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

    TRANSITS

    Parts of a transit

    THEODOLITES

    Compared to transits, theodolites are
    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:

    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'

    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
  • 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