---
title: "Definition of trilateration term"
subject: "Surveying I"
chapter: 8
key: "semester_3/surveying_i:define-trilateration"
source: https://www.bctengineer.com/q/semester_3/surveying_i/define-trilateration
site: BCT Engineering
---

# Definition of trilateration term

Surveying I · Chapter 8: Triangulation and Trilateration

- Asked in: 2067 Asar, 2 marks
- Video: [Trilateration & Triangulation](https://www.youtube.com/watch?v=O5FHPEPQUgk) — St.Thomas ITI Kanhirapuzha
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/define-trilateration
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-8

## Question

Define trilateration.

## Short answer

Trilateration is a horizontal control survey method where all sides of a chain or net of triangles are measured directly with an electromagnetic distance measurement (EDM) instrument, and the angles are then computed from the measured sides using the cosine rule, with no angle observations in the field.

## Answer

**Trilateration** is a method of horizontal control survey in which the lengths of all the sides of a chain or net of triangles are measured directly with an EDM instrument, and the angles of the triangles are then computed from the measured sides using the cosine rule. No angles are observed in the field.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is measured directly in trilateration?
   A. Lengths of all sides with an EDM
   B. All angles
   C. Only the base line
   D. Only bearings
   Answer: A. All sides of the triangles are measured directly by EDM. (Key point: Definition)

2. How are the triangle angles obtained in trilateration?
   A. Measured by theodolite
   B. Computed from the sides using the cosine rule
   C. Taken from a map
   D. Computed by the sine rule from one angle
   Answer: B. No angles are observed in the field; the cosine rule gives them. (Key point: Angles computed)

3. Trilateration is a method of what type of survey?
   A. Vertical control
   B. Hydrographic only
   C. Horizontal control
   D. Soil survey
   Answer: C. It fixes horizontal positions of stations in a net of triangles. (Key point: Type of survey)

## Related in Surveying I

- [Definition of meridian term](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Adefine-meridian) — Surveying I, chapter 4

## Related in other subjects

- [Technology definition and change in culture](https://www.bctengineer.com/question.md?key=semester_7%2Ftechnology_environment_and_society%3Adefine-tech-culture-traditions) — Technology, Environment and Society, chapter 1