Geometric fundamentals of Photogrammetry; Elements of Vertical Photograph; Relief displacement, Image Parallax, Stereo model- Photo mosaics; Image interpretation Keys; Ground Control for Aerial Photography

1. Geometric Fundamentals of Photogrammetry

The geometric fundamentals of photogrammetry explain how 3D ground features are represented as 2D images using the principles of perspective geometry.

Perspective projection – Formation of an image from a single camera position.
Camera station (Exposure station) – Position of the camera during exposure.
Principal point – Centre of the photograph.
Principal axis – Line joining the camera lens and principal point.
Focal length (f) – Distance between the camera lens and image plane.
Scale – Ratio of image distance to ground distance.

Concept:
Photogrammetry uses camera geometry to measure distances, heights, and coordinates accurately.

2. Elements of Vertical Photograph

A vertical photograph is taken with the camera axis nearly perpendicular (90°) to the Earth's surface.

Key Elements

Principal point (PP)
Nadir point (NP)
Isocentre (IC)
Fiducial marks
Photo centre
Flight line
Scale
Overlap (Forward and Side overlap)

Concept:
These elements help determine image orientation and accurate mapping.

3. Relief Displacement

Relief displacement is the apparent outward movement of objects from the centre of a photograph due to differences in elevation.

Height (H)
Flying height (h)
Radial displacement
Photo centre

Concept:
Higher objects (buildings, trees, hills) appear displaced farther from the photo centre than lower objects.

4. Image Parallax

Parallax is the apparent shift in the position of an object between two overlapping photographs.

Absolute parallax
Differential parallax
Air base
Stereo pair

Concept:
Parallax is used to calculate the height and elevation of ground features.

5. Stereo Model

A stereo model is a three-dimensional (3D) view created by observing two overlapping aerial photographs.

Stereo pair
Binocular vision
Stereoscope
Base-height ratio

Concept:
The stereo model enables accurate measurement of terrain height, slope, and landforms.

6. Photo Mosaics

A photo mosaic is a composite image formed by joining several overlapping aerial photographs into one continuous image.

Types:

Uncontrolled mosaic
Semi-controlled mosaic
Controlled mosaic

Concept:
Photo mosaics provide a larger and continuous view for mapping and land-use studies.

7. Image Interpretation Keys

Image interpretation keys are the visual characteristics used to identify objects in aerial photographs or satellite images.

Tone/Colour
Texture
Shape
Size
Pattern
Shadow
Site
Association

Concept:
These keys help distinguish natural and human-made features accurately.

8. Ground Control for Aerial Photography

Ground control refers to accurately surveyed reference points on the Earth's surface used to correct and georeference aerial photographs.

Ground Control Points (GCPs)
GPS/GNSS
Coordinates
Georeferencing
Image rectification
Check points

Concept:
Ground control improves the positional accuracy of aerial photographs and ensures reliable photogrammetric mapping.

Comments

CREATION OF SPATIAL DATA

Spatial data creation is the process of generating, organizing, and managing geographically referenced information in a Geographic Information System (GIS). It involves converting maps, satellite images, GPS observations, and field survey data into digital datasets that can be stored, analyzed, and visualized. The quality of GIS analysis depends largely on the accuracy of spatial data creation. 1. Creation of Shapefile and Geodatabase A. Shapefile A Shapefile is one of the most widely used vector data formats developed by Esri for storing geographic features. Definition A shapefile stores the geometry and attributes of geographic features such as points, lines, and polygons. Components of a Shapefile A shapefile consists of several files: .shp – Stores geometry (shape) .shx – Shape index .dbf – Attribute table .prj – Coordinate Reference System (CRS) .sbn/.sbx – Spatial index (optional) Geometry Types Point – W...

Geography of Health or Medical Geography

Health Geography (also known as Medical Geography ) is a sub-discipline of Human Geography that studies the relationships between place, environment, society, and health . It examines how spatial location, environmental conditions, and social and economic factors influence human health, disease patterns, and access to healthcare services. Health geography integrates concepts from geography, epidemiology, medicine, public health, environmental science, sociology, and Geographic Information Systems (GIS) to understand and improve population health. Major Components of Health Geography Health geography is generally divided into two major branches : The Geography of Disease and Ill Health The Geography of Health Care 1. The Geography of Disease and Ill Health This branch studies the spatial distribution, determinants, and diffusion of diseases across different geographical scales, from neighborhoods to global regions. It seeks t...

Nature and Scope of Geography

Geography is the scientific study of the Earth's surface, its physical features, human populations, and the interactions between people and their environment. The word Geography is derived from the Greek words Geo (Earth) and Graphien (to describe or write), meaning "description of the Earth." Modern geography goes far beyond description; it seeks to explain where phenomena occur, why they occur there, how they are spatially distributed, and how they change over time. Geography is regarded as a spatial science , an environmental science , and an integrative discipline because it bridges natural sciences, social sciences, and geospatial technologies. Nature The nature of geography refers to the characteristics and fundamental features that define the discipline. 1. Geography as a Spatial Science Terminology: Spatial Science A discipline concerned with the location, distribution, arrangement, organization, and interaction of phenomena in ...

Historical Development of Geography in the Ancient Period

The Ancient Period marks the earliest stage in the evolution of geographical thought, extending from approximately 3000 BCE to the 5th century CE . During this period, geography evolved from simple descriptions of the Earth's surface to systematic scientific inquiry. Early civilizations developed geographical knowledge to meet practical needs such as navigation, trade, agriculture, military expansion, taxation, and administration . The greatest contributions came from the Mesopotamian, Egyptian, Indian, Chinese, Greek, and Roman civilizations , with the Greeks laying the foundations of scientific geography . Meaning Terminology: Historical Development Historical development refers to the gradual evolution of geographical knowledge, concepts, methods, and theories over time. Concept Geographical knowledge evolved through: Observation of the natural environment Exploration and travel Cartography (map-making) Astronomical observations ...

Development of Health Geography

Health Geography (formerly Medical Geography ) is the branch of geography that studies the relationship between health, disease, environment, place, and healthcare systems . The discipline has evolved over more than 2,500 years through contributions from physicians, geographers, epidemiologists, microbiologists, and public health experts. The development of Health Geography can be divided into the following periods: Ancient Period Medieval Period Renaissance and Pre-Modern Period Nineteenth Century (Pre-World War Era) World War Period Post-World War Period Modern Health Geography 1. Ancient Period (5th Century BC – 500 AD) Characteristics Health closely linked with the natural environment. Diseases explained through climate, water, air, and seasons. No knowledge of microorganisms. Medical observations were descriptive. Major Concepts Environmental Determinism Disease Ecology Climate and Healt...

Vineesh V, Geography

Search This Blog