--- title: "Selection of triangulation stations; applications" subject: "Surveying I" chapter: 8 key: "semester_3/surveying_i:selection-of-triangulation-stations" source: https://www.bctengineer.com/q/semester_3/surveying_i/selection-of-triangulation-stations site: BCT Engineering --- # Selection of triangulation stations; applications Surveying I · Chapter 8: Triangulation and Trilateration - Asked in: 2075 Asoj, 4 marks - Video: [ADVANCE SURVEY (18CV45) - selection and marking of triangulation station](https://www.youtube.com/watch?v=6KS5j085kmQ) — Bearys Institute of Technology - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/surveying_i/selection-of-triangulation-stations - Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-8 ## Question Describe selection criteria of triangulation and trilateration stations. What are the field applications of triangulation? ## Short answer Stations must be intervisible, form well-conditioned triangles (angles 30°–120°), on stable accessible ground and high enough to clear obstructions; for trilateration, line of sight must be clear for EDM beam. Triangulation provides control for topographic mapping, establishes positions of structures, sets out long engineering works, and supports geodetic, hydrographic and photogrammetric surveys. ## Answer #### Selection of triangulation / trilateration stations 1. **Intervisibility:** every station should be visible from the adjacent stations; hills, high buildings or towers can be used, and the line of sight should clear the ground, trees and buildings (by at least a few metres, to avoid refraction near the ground). 2. **Well-conditioned triangles:** the angles should lie between 30 and 120 degrees (preferably 45 to 90); avoid long, thin triangles. 3. **Stability and accessibility:** stations should be on firm ground that will not settle, easy to reach with the instrument and signals, and have enough space to erect the signal. 4. **Height:** stations should be high enough to see over obstructions, but not so high that tower cost or access becomes a problem; keep the number of stations to a minimum. 5. **Base line:** the base line site should be nearly level and free from obstacles, near the centre of the area, so that the base can be extended into the net. 6. **For trilateration:** the line of sight must be clear for the EDM beam, free from strong reflecting surfaces, power lines or heat sources close to the beam, and the temperature and pressure should be measurable at both ends. 7. **Permanence:** stations should be placed so that they can be used for future survey work and are safe from disturbance and construction. #### Field applications of triangulation - Providing control points for topographic mapping and large-scale surveys. - Fixing the accurate positions of towns, boundaries, bridges and dams. - Setting out long bridges, tunnels, and the centre lines of dams or canals. - Geodetic work: size and shape of the earth, latitude, longitude and azimuth. - Hydrographic surveys: fixing soundings and shore points from shore stations. - Photogrammetric control for aerial mapping. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why must adjacent stations be intervisible, with the line of sight clear of the ground? A. To reduce the cost of chaining B. So that observations can be made and ground refraction is avoided C. To increase the size of triangles D. To avoid using signals Answer: B. Stations must be visible to each other and sight lines should clear the ground to avoid refraction. (Key point: Intervisibility) 2. Which range of angles gives well-conditioned triangles? A. Below 30 degrees B. Between 120 and 170 degrees C. Between 30 and 120 degrees D. Only exactly 90 degrees Answer: C. Angles between 30 and 120 degrees (preferably 45 to 90) avoid long thin triangles. (Key point: Well-conditioned triangles) 3. What is an additional requirement for trilateration stations? A. Stations in valleys B. Very thin triangles C. No need for line of sight D. Beam path free from strong reflecting surfaces and heat sources, with temperature and pressure measurable at both ends Answer: D. EDM beam must be undisturbed and meteorological data available for correction. (Key point: Trilateration station criteria) 4. Which is a field application of triangulation? A. Setting out long bridges, tunnels and dam centre lines B. Measuring soil moisture C. Counting traffic D. Designing a roof truss Answer: A. Triangulation gives accurate control for setting out large engineering works and mapping. (Key point: Field applications) ## Related in Surveying I - [Triangulation versus trilateration](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atriangulation-vs-trilateration) — Surveying I, chapter 8, asked 7× - [Triangulation, trilateration; specifications](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atriangulation-trilateration-specifications) — Surveying I, chapter 8, asked 5× - [Triangulation principle; 1st order trilateration](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atriangulation-principle-first-order-trilateration) — Surveying I, chapter 8 - [Trilateration over triangulation; primary specs](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atrilateration-advantages-primary-triangulation) — Surveying I, chapter 8 - [Triangulation; EDM principle for trilateration sides](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atriangulation-and-edm-principle-trilateration) — Surveying I, chapter 8 - [Principle of triangulation and trilateration](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aprinciple-triangulation-trilateration-note) — Surveying I, chapter 8 ## Related in other subjects - [Selection criteria for ADC](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aadc-selection-criteria) — Instrumentation II, chapter 4, asked 3× - [Selection criteria of hydraulic turbines](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aturbine-selection-criteria) — Hydro Power, chapter 7, asked 2× - [Draft tube function and turbine selection criteria](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Adraft-tube-turbine-selection) — Hydro Power, chapter 7 - [Criteria for site selection](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asite-selection-criteria) — Building Technology, chapter 1