How do you measure distances using a total station?

Short Answer:

Measuring distances with a total station involves using its built-in Electronic Distance Measurement (EDM) system to calculate the space between the instrument and a target prism or reflective surface. First, the surveyor sets up and levels the total station over a known point, then sights the target prism placed at the point to be measured.

When the instrument emits an infrared or laser beam toward the prism, it times the return signal and computes the horizontal and slope distances automatically. Readings are displayed on the instrument screen and can be stored digitally for mapping and layout tasks.

Detailed Explanation:

Distance Measurement

A total station combines an electronic theodolite with an EDM unit. The EDM sends a modulated infrared or laser beam to a reflective prism or directly to a surface (reflectorless mode). When the beam returns, the instrument measures the phase shift or time of flight, converting it to precise distance values. Total stations typically measure slope distance, horizontal distance, and vertical angle, allowing surveyors to derive elevations and plan positions accurately.

Before any measurement, ensure the total station is properly calibrated and the tripod is stable. Calibration checks for EDM accuracy, vertical circle index, and compensator function. A level bubble or electronic tilt sensor confirms the instrument is exactly vertical. The surveyor enters atmospheric parameters—temperature, pressure, and humidity—to correct for refraction and ensure distance accuracy.

Field Procedure

  1. Setup and Leveling: Place the tripod over a known station. Mount the total station and use leveling screws to center the bubble or activate the electronic level sensor.
  2. Orientation: Aim the instrument at a reference back-sight point (another known station) and record its horizontal angle as zero. This establishes the instrument’s orientation.
  3. Targeting the Prism: Place the prism pole at the point you want to measure. Adjust the total station crosshairs until they precisely align with the prism’s center. In reflectorless mode, aim at the marked spot on the surface.
  4. Distance Measurement: Trigger the EDM function. The instrument fires the beam, receives the return, and instantly calculates the slope distance. The onboard computer then applies trigonometric functions using the vertical angle to compute horizontal distance and elevation difference.
  5. Recording Data: Each reading is stored in the total station’s memory with point codes or descriptions. Later, this data can be downloaded to mapping software for plan preparation, volume calculations, or construction staking.

Accuracy depends on the quality of the prism, atmospheric corrections, and instrument calibration. Reflectorless measurements are convenient for inaccessible points but may have slightly lower precision. Regularly checking calibration and using high-quality prisms improve reliability.

Conclusion:

Using a total station to measure distances streamlines surveying by integrating angle measurement and EDM. Proper setup, leveling, orientation, and target alignment ensure accurate distance readings. With digital storage and real-time corrections, total stations provide fast, precise data for mapping, construction layout, and engineering projects.