Module 1 : Modern Surveying Equipment
 Lecture 1 : Introduction
Digital levels
  • Traditionally various types of levels have been used for measurement of elevation differences such as
    • dumpy level
    • tilting level
    • automatic level
  • Recently electronic digital levels have evolved as a result of development in electronics and digital image processing.
  • Digital levels use electronic image processing to evaluate the special bar-coded staff reading. The observer is in effect replaced by a detector diode array, which derives a signal pattern from the bar-coded levelling staff. This bar-coded pattern is converted into elevation and distance values using a digital image matchingprocedure within the instrument. Automatic data conversion eliminates personal errors in reading the staff and the field data is stored by the instrument on its recording medium, thus further eliminating booking errors (Schoffield, 2002).
Salient features of digital levels
  • A digital level offers the following advantages compared to the conventional levelling and recording procedures:
    • Fatigue-free observation as visual staff reading by the observer is not required.
    • User friendly menus with easy to read, digital display of results.
    • Measurement of consistent precision and reliability due to automation.
    • Automatic data storage eliminates booking and its associated errors.
    • Automatic reduction of data to produce ground levels, thereby eliminating arithmetical errors.
    • Fast, economic surveys resulting in saving in time (up to 50% less effort has been claimed by manufacturers)
    • Data on the storage medium of the level can be downloaded to a computer enabling quick data reduction for various purposes.
    • Digital levels can also be used as conventional levels with the help of dual marked staff (bar coded on one side of the staff for automated reading and conventional graduation on other side of the staff) in case it is difficult to record readings digitally (e.g. for long distances).