--- title: "Triangulation versus trilateration" subject: "Surveying I" chapter: 8 key: "semester_3/surveying_i:triangulation-vs-trilateration" source: https://www.bctengineer.com/q/semester_3/surveying_i/triangulation-vs-trilateration site: BCT Engineering --- # Triangulation versus trilateration Surveying I · Chapter 8: Triangulation and Trilateration - Asked in: 2081 Baisakh, 4 marks; 2078 Kartik, 4 marks; 2069 Chaitra, 4 marks; 2068 Baisakh, 4 marks; 2063 Baisakh, 8 marks; 2061 Baisakh, 8 marks; 2059 Chaitra, 6 marks (asked 7 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/surveying_i/triangulation-vs-trilateration - Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-8 ## Question Differentiate between triangulation and trilateration (with advantages and disadvantages). ## Short answer Triangulation measures a single base line and all angles, then computes sides by the sine rule; it is time‑consuming and needs clear visibility. Trilateration measures all sides directly with an EDM instrument and computes angles by the cosine rule; it is faster, works in poor visibility with microwave, but requires costly instruments and atmospheric corrections. ## Answer **Triangulation** is a method of horizontal control survey in which control stations are fixed at the vertices of a chain or net of triangles. One side (the **base line**) is measured very accurately, all the angles of the triangles are measured, and the lengths of the other sides are computed with the sine rule. **Trilateration** is the method in which the lengths of **all the sides** of the triangles are measured directly with an EDM (electromagnetic distance measuring) instrument, and the angles are computed from the sides using the cosine rule. #### Differences | Basis | Triangulation | Trilateration | |---|---|---| | Measured quantities | One base line and all angles | All sides of all triangles | | Instrument | Theodolite (precise) | EDM / total station | | Computed quantities | Other sides (sine rule) | Angles (cosine rule) | | Control | Check base line at the end | Closure of the figure; no separate base | | Weather | Needs good visibility for signals; angles affected by refraction | Atmospheric conditions (temperature, pressure) affect the measured distance; works in poor visibility with microwave EDM | | Field work | Time-consuming; many angles observed in sets | Fast; each side measured in minutes | | Accuracy | Depends on angle measurement; errors accumulate with distance | Distances very accurate with modern EDM; better control of scale | | Orientation | Azimuth must be observed | Azimuth must be observed separately (no angles) | | Cost | Higher fieldwork cost | Lower fieldwork cost today | **Advantages of triangulation:** needs only one base line; theodolite angle measurement is reliable; suitable for large areas; well-established practice. **Disadvantages of triangulation:** base line measurement is laborious; angular observation is slow and needs signals/towers; errors accumulate. **Advantages of trilateration:** quick, with no angle measurement or base-line extension; EDM gives high accuracy; works in low visibility (microwave); needs fewer observers. **Disadvantages of trilateration:** needs costly EDM; atmospheric corrections are necessary; fewer checks on gross errors unless the figure has redundant sides; gives no azimuth. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is measured in triangulation, compared with trilateration? A. Triangulation: one base line and all angles; trilateration: all sides B. Triangulation: all sides; trilateration: all angles C. Both measure only angles D. Triangulation: only angles with no base line; trilateration: only bearings Answer: A. Triangulation needs a base line and angles; trilateration measures every side by EDM. (Key point: Quantities measured) 2. Which rule computes the unknown quantities in each method? A. Cosine rule in triangulation; sine rule in trilateration B. Sine rule for sides in triangulation; cosine rule for angles in trilateration C. Sine rule in both D. Pythagoras in both Answer: B. Sides follow from base and angles by the sine rule; angles follow from three sides by the cosine rule. (Key point: Computation) 3. Which is a disadvantage of trilateration? A. Needs a long base line B. Needs slow observation of many angle sets C. Needs costly EDM and atmospheric corrections to the distances D. Cannot give any distances Answer: C. EDM distances are affected by temperature and pressure and the equipment is expensive. (Key point: Disadvantage of trilateration) 4. Which is a disadvantage of triangulation? A. It needs no base line B. It cannot be used over large areas C. It needs EDM for every side D. Base line measurement is laborious and angle observation is slow Answer: D. Triangulation needs an accurately measured base and signals and slow angle observation. (Key point: Disadvantage of triangulation) ## Related in Surveying I - [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 - [Triangulation, trilateration, graphical intersection](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atriangulation-trilateration-graphical-intersection-pt) — Surveying I, chapter 8