JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III GEOINFORMATICS Previous Question Paper (February/March - 2022 - R16)

Stereoscopic parallax is the apparent displacement of the position of an object relative to a reference point or system caused by a change in the observer's position. In aerial photography, it is the change in the position of an image of an object on successive overlapping photographs due to the movement of the aircraft between exposures.

The fundamental principle relies on the parallax displacement, which occurs radially from the nadir point of the photograph. Because the aircraft moves along a flight line, the same ground object is captured from two different vantage points. When these two overlapping images are viewed through a stereoscope, the brain fuses the two slightly different perspectives to perceive depth, creating a three-dimensional model known as a stereomodel.

Key characteristics include:

• The displacement is always parallel to the line of flight.
• Objects closer to the camera (higher elevation) exhibit greater parallax displacement than objects at lower elevations.
• The formula for parallax is given by:

Where p is the parallax, f is the focal length of the camera, B is the air base (distance between exposure stations), and H is the flying height above the object. This phenomenon is the basis for measuring heights of objects and creating topographic maps from aerial photographs.

Aerial photo-interpretation is the act of examining photographic images for the purpose of identifying objects and judging their significance. It relies on the systematic analysis of visual cues to extract information about the Earth's surface.

The fundamental principles (elements) of interpretation include:

• Shape: The general form or outline of an object, which often allows for immediate identification (e.g., a runway vs. a road).
• Size: The relative or absolute dimensions of an object, which helps distinguish between similar shapes (e.g., a small shed vs. a large warehouse).
• Tone/Color: The relative brightness or color of objects, which reflects the reflectance properties of the surface.
• Texture: The frequency of tonal change, providing a sense of roughness or smoothness (e.g., forest canopy vs. grassland).
• Pattern: The spatial arrangement of objects, whether natural or man-made (e.g., orchard planting patterns).
• Shadow: Provides a profile view of objects, aiding in the identification of height and shape.
• Association: The relationship between an object and its surroundings (e.g., a water tower is often associated with a railway station).

The primary objectives of photo-interpretation are to identify, classify, and delineate features on the ground, facilitate the mapping of land use and land cover, monitor environmental changes over time, and support resource management such as forestry, agriculture, and urban planning.