Total Station Surveying: Distance Measurement and Planimetric Methods
Reflectors in Total Station Surveying
Reflectors are optical mirror prisms located on a pole. These can be single prisms or groups of prisms, the latter used to increase the distance measurement range. Each prism has a constant correction factor that must be entered into the Electronic Distance Measurement (EDM) configuration.
Errors in Distance Measurement
Errors in Direct Measurement with Tape: Experiments show that the linear error E on a measured length (L) may have specific values, depending on the terrain and conditions.
Errors in Indirect Measurement with EDM: The absolute error can be expressed as:
Expressed in mm: Where:
- A = fixed part of accuracy (mm)
- B = proportion of the distance (parts per million)
- D = distance measured (km)
The relative error is calculated as:
rugged terrain or horizontal ‘0 ‘000032 0078 nte 0022 Land sensibleme ‘000032 ‘0 L LLELLL ETL TL 2 2) (AED mm mm DB DEED RD
Planimetric Methods with Total Station Surveying
Radiation Method
The objective of radiation is to obtain planimetric coordinates of a series of points representing the ground. This method requires a point of known coordinates materialized in the field and a known orientation or another point of known coordinates to guide the instrument’s azimuth.
The data obtained includes horizontal angle, vertical angle, and slope distance. The methodology involves setting up the instrument, orienting it using a known reference point, and then taking readings of representative points, noting horizontal angles, vertical angles, and slope distances. After completing the work, the reference point should be re-sighted to check for any instrument movement. If movement is detected, all observations must be discarded. A drawback of this method is the lack of inherent verification, unlike other methods. The coordinates obtained are polar, requiring conversion to Cartesian coordinates by calculating the increments of X and Y.
Traverse Method
Traverses are used to determine the coordinates of points used for radiation or other operations. A traverse, or polygon, is essentially a series of chained radiations. There are several types of traverses:
- Closed Traverse: Begins and ends at the same point, allowing for error evaluation.
- Framed Traverse: Begins and ends at points with known coordinates and references, also allowing for error determination.
- Hanging Traverse: Starts at a reference point with known coordinates but ends at a point with unknown coordinates, making error evaluation impossible.
The methodology for conducting a traverse involves setting up the instrument at the starting point (B1), orienting it to a known reference (Ref1), and then sighting the second point of the traverse (B2), obtaining horizontal angles, vertical angles, and slope distance. The instrument is then moved to the next point.