---
title: "Short note: Photo scale, photogrammetry uses"
subject: "Surveying II"
chapter: 7
key: "semester_4/surveying_ii:photo-scale-photogrammetry-uses"
source: https://www.bctengineer.com/q/semester_4/surveying_ii/photo-scale-photogrammetry-uses
site: BCT Engineering
---

# Short note: Photo scale, photogrammetry uses

Surveying II · Chapter 7: Photogrammetry and Remote Sensing

- Asked in: 2075 Baisakh, 4 marks
- Video: [Basics of Photogrammetry: Everything You Need to Know!](https://www.youtube.com/watch?v=t-x_9aXr2hM) — GIS Resources
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/surveying_ii/photo-scale-photogrammetry-uses
- Whole chapter: https://www.bctengineer.com/md/semester_4/surveying_ii/chapter-7

## Question

Write a short note on the scale of vertical photograph and uses of photogrammetry.

## Short answer

The scale of a vertical photograph is S = f/(H-h) and varies with terrain. Photogrammetry is used for topographic mapping, route and site selection, volume measurement, land-use and cadastral surveys, and disaster assessment.

## Answer

#### Scale of a vertical photograph
The scale of a vertical photograph is the ratio of a distance on the photo to the same distance on the ground. By similar triangles in the camera,

$$
S = \frac{\text{photo distance}}{\text{ground distance}} = \frac{f}{H-h}
$$

where $f$ is the focal length of the camera, $H$ is the flying height above the datum and $h$ is the elevation of the ground above the datum. The scale varies from point to point when the terrain is not flat, and is larger for higher ground. If $h = 0$, $S = f/H$.

#### Uses of photogrammetry
- Preparation of topographic maps and contour maps, and orthophotos.
- Route location for roads, railways, pipelines and canals.
- Site selection for dams, bridges and airports.
- Measuring volumes (earthwork, stockpiles) and cross-sections.
- Mapping of inaccessible, hazardous or very large areas.
- Land use, forestry, geology and urban planning surveys.
- Cadastral and property mapping; disaster damage assessment.
- Close-range photogrammetry: structural deformation, monuments and archaeology.

## Check yourself

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

1. Scale of a vertical photograph is:
   A. (H-h)/f
   B. f/(H-h)
   C. f x (H-h)
   D. H/f
   Answer: B. S = f/(H-h) from similar triangles. (Key point: Scale formula)

2. On non-flat terrain, where is the scale larger?
   A. Lower ground
   B. Same everywhere
   C. At the principal point only
   D. Higher ground
   Answer: D. Higher ground has smaller H-h, so scale f/(H-h) is larger. (Key point: Scale and elevation)

3. Which is a use of photogrammetry?
   A. Soil compaction testing
   B. Topographic/contour maps and orthophotos
   C. Concrete mix design
   D. Water treatment
   Answer: B. Mapping, route location, volume measurement and many more are uses. (Key point: Uses)

4. Close-range photogrammetry is used for:
   A. Mapping provinces
   B. Aerial route survey
   C. Satellite orbit tracking
   D. Structural deformation and monuments
   Answer: D. Ground-based cameras document structures, monuments and archaeology. (Key point: Close-range)

## Related in Surveying II

- [Expression for scale of vertical photograph](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Avertical-photograph-scale-expression) — Surveying II, chapter 7
- [Types of aerial photograph, scale relation](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aaerial-photo-types-scale-relation) — Surveying II, chapter 7
- [Flying height from photo and map scale](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aflying-height-pq-20cm-focal-24) — Surveying II, chapter 7
- [Short note: Importance and uses of photogrammetry](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aphotogrammetry-importance-uses) — Surveying II, chapter 7
- [Short note: Photogrammetry limitation and uses](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aphotogrammetry-limitations-uses) — Surveying II, chapter 7
- [Relief displacement on a vertical photograph](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Arelief-displacement-sketch-vertical-photo) — Surveying II, chapter 7