--- title: "Plane and geodetic surveying; principles" subject: "Surveying I" chapter: 1 key: "semester_3/surveying_i:plane-geodetic-and-principles" source: https://www.bctengineer.com/q/semester_3/surveying_i/plane-geodetic-and-principles site: BCT Engineering --- # Plane and geodetic surveying; principles Surveying I · Chapter 1: Introduction - Asked in: 2066 Bhadra, 8 marks; 2066 Jestha, 7 marks; 2065 Shrawan, 8 marks; 2063 Baisakh, 4+4 marks; 2062 Baisakh, 6 marks; 2061 Baisakh, 6 marks; 2058 Chaitra, 6 marks (asked 7 times) - Video: [Principles of Surveying || Civil Engineering Basics](https://www.youtube.com/watch?v=hAIhrFHPV0s) — Civil Engineering Fanatics - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/surveying_i/plane-geodetic-and-principles - Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-1 ## Question What are plane and geodetic surveying? Explain the principles of surveying. ## Short answer Plane surveying treats the earth as flat for areas under 250 km², using plane trigonometry. Geodetic surveying accounts for curvature over larger areas with high precision and spherical trigonometry. The principles are working from whole to part and locating points by at least two independent measurements from known references. ## Answer #### Plane surveying Plane surveying is the type of surveying in which the earth's surface is treated as a **plane**, so the curvature of the earth is neglected. The level line is taken as a straight line, the angles of a triangle sum to $180^\circ$ and plane trigonometry is used. It is suitable for areas up to about 250 km$^2$ (about 15.8 km $\times$ 15.8 km), where the difference between an arc and its chord is negligible. Examples: road, canal, building-site and small town surveys. #### Geodetic surveying Geodetic surveying is the type of surveying in which the **curvature of the earth** (its spheroidal shape) is taken into account. Precise instruments and methods are used, the lines are treated as arcs and spherical trigonometry is used. It is used for large areas above about 250 km$^2$, for fixing widely spaced control points (latitude, longitude, elevation) and for national mapping. The angles of a triangle sum to more than $180^\circ$ (spherical excess). #### Principles of surveying The two basic principles are: 1. **Working from whole to part.** A strong main framework (control network) of a few stations is first established over the whole area with high accuracy. The smaller parts and details are then surveyed inside it with less accurate methods. Errors are therefore controlled, and a mistake in one part does not spread to the others. Working from part to whole would let errors accumulate and grow. Example: a main triangulation or main traverse is made first, then chain lines and offsets locate the details inside each triangle. 2. **Location of a point by at least two measurements from fixed reference points.** A new point is fixed relative to two known points by two distances (linear intersection), two angles (angular intersection), a distance and an angle, or a perpendicular offset and a chainage. A third measurement is taken as a check. Example: Point C is fixed from A and B by measuring distances AC and BC; the check is the distance from C to a point on AB. Other working rules follow from these: take every measurement twice or by a different method (as a check), and keep the accuracy of the work consistent with the purpose of the map. ```text Point C fixed from A and B C /|\ b / | \ a by distances a and b / | \ A---+---B check: tie distance ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In plane surveying, how is the earth's surface treated? A. As a spheroid with spherical trigonometry B. As a plane but with spherical excess added C. As a plane, with curvature neglected and angles of a triangle summing to 180° D. As a sphere only for levelling Answer: C. Plane surveying neglects curvature and uses plane trigonometry. (Key point: Plane surveying assumption) 2. Which statement about geodetic surveying is correct? A. It considers earth's curvature, covers areas above about 250 km^2 and gives triangle angles summing to more than 180° B. It ignores curvature and is used for areas under 250 km^2 C. It uses plane trigonometry and ordinary instruments D. Its triangles have angle sum less than 180° Answer: A. Geodetic work uses spherical trigonometry, so there is spherical excess in the triangle angle sum. (Key point: Geodetic surveying) 3. Why is the 'working from whole to part' principle followed? A. It lets the details be measured with the most precise instruments B. Errors do not accumulate, and a mistake in one part stays inside that part C. It removes the need to check measurements D. It makes the survey cheaper because no control stations are required Answer: B. A precise control framework is fixed first and details are fitted inside it, so errors are localised instead of adding up. (Key point: Why whole to part) 4. Point C is fixed from A and B by distances AC and BC. What is the check? A. The sum of AC and BC B. The angle sum at A and B C. A repeat of the same AC measurement only D. The distance from C to a point on AB Answer: D. A tie distance from C to a point on AB is an extra measurement that checks the fixing. (Key point: Fixing point C) ## Related in Surveying I - [Plane versus geodetic surveying](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aplane-vs-geodetic-surveying) — Surveying I, chapter 1, asked 5× - [Objectives of surveying; plane vs geodetic](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobjectives-plane-geodetic) — Surveying I, chapter 1 - [Principles of surveying with examples](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aprinciples-of-surveying) — Surveying I, chapter 1, asked 9× - [Principles of surveying; scales used](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aprinciples-and-scales-used) — Surveying I, chapter 1 - [Plane table principles; orientation by back sighting](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aorientation-back-sighting) — Surveying I, chapter 6, asked 4× - [Plane table principles; advantages, disadvantages](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aprinciples-adv-disadv-plane-table) — Surveying I, chapter 6, asked 2×