Mine Development & Surveying

GIS & Remote Sensing Basics

Raster vs vector data, spectral bands and the photo-scale relation that converts an aerial image into ground distances.

PART 1

Topic Breakdown & Traps

The Engineering Principle

GIS (Geographic Information Systems) store spatial data in two models: vector (points, lines, polygons — sharp boundaries like lease limits and benches) and raster (a grid of cells/pixels, each holding a value — elevation, reflectance). Remote sensing acquires information without contact, recording reflected/emitted energy in discrete spectral bands (visible, NIR, SWIR, thermal). Resolution is described as spatial (pixel ground size / GSD), spectral (number and width of bands), radiometric and temporal. Photogrammetry links an aerial photo to the ground through the scale relation

S = f / H = ℓ / L

, the basis for measuring distances and areas off imagery.

The Core Formula Matrix

Photo scale:

S = \frac{f}{H} = \frac{ℓ}{L}

(

f

= focal length,

H

= flying height above ground;

ℓ

= photo distance,

L

= ground distance)

Representative fraction: a scale of 1:25,000 means

1 cm

on the photo =

25, 000 cm = 250 m

on the ground.

Ground distance:

L = \frac{ℓ}{S} = ℓ \times \frac{H}{f}

Ground area:

A_{g r o u n d} = A_{p h o t o} \times (\frac{1}{S})^{2}

(area scales with the square).

The ‘IIT Traps’

⚠
**Scale is a ratio $f / H$ — flying height is above the ground**, not above sea level; ignoring terrain elevation biases the scale.
⚠
Area scales as the square of the scale factor, not linearly. Forgetting the square underestimates area by orders of magnitude.
⚠
Larger denominator = smaller scale. 1:50,000 is a *smaller* scale (less detail) than 1:10,000.
⚠
Raster vs vector. Continuous fields (DEMs, reflectance) suit raster; discrete features (boundaries, roads) suit vector.

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

In a GIS, a continuously varying surface such as a Digital Elevation Model is best represented by which data model?

Q2MEDIUM2 Marks · NAT

An aerial camera of focal length

150 mm

flies at a height of

1500 m

above the ground. The representative fraction of the photograph is

1 : n

, where

n

is ______. (Round to the nearest whole number.)

Q3HARD2 Marks · NAT

On a photograph of scale

1 : 10, 000

, a rectangular waste dump measures

4.0 cm \times 3.0 cm

. Its actual ground area is ______ hectares. (Round off to one decimal place.)