Why is overlap in aerial photography necessary

The terrain has an average elevation of m above mean sea level. The flying altitude of the aircraft above mean sea level during photograph will be. Suggested Test Series. Suggested Exams. More Surveying Questions Q1. Match the lists and select the correct option. The staff readings taken are given below. The process of determining the plotted position of the station occupied by the plane table by means of sights taken towards points of known location is called :.

Which of the following statements is correct? Which of the following types of levelling cannot be done with a dumpy level? Lecture on photogrammetry. T5 sampling. Photogrammetry 1. Introduction of photogrammetry. Photogrammetry- Surveying. Principle of aerial photography and types. Related Books Free with a 30 day trial from Scribd. Related Audiobooks Free with a 30 day trial from Scribd. Jaanu Moonlover. A Adediji. Prabjeet Singh. Sathish Kumar.

Surendra Kolavali. Show More. Views Total views. Actions Shares. No notes for slide. Lecture 1-aerial photogrammetry 1. S updated and done this way. Aerial camera Types of Aerial Photographs Principle of Aerial survey Definitions Photo nadir point n : It is a point on photograph obtained by dropping vertical line from camera center.

Definitions Azimuth : A : Clockwise horizontal angle measured about ground nadir point from true north to the principal plane of photograph. Scale of Photograph Scale of a Vertical Photo Specifically, the higher the elevation of an object, the farther the object will be displaced from its actual position away from the principal point of the photograph the point on the ground surface that is directly below the camera lens.

This effect, called relief displacement , is illustrated in the diagram below. Note that the effect increases with distance from the principal point. Equation for relief displacement d Ground speed of aeroplane Time interval of successive photographs Overlaps Large Scale - Larger-scale photos e.

A large scale photo simply means that ground features are at a larger, more detailed size. The area of ground coverage that is seen on the photo is less than at smaller scales.

Small Scale - Smaller-scale photos e. A small scale photo simply means that ground features are at a smaller, less detailed size. The area of ground coverage that is seen on the photo is greater than at larger scales.

The National Air Photo Library has a variety of photographic scales available, such as large scale of selected areas, and small scale. Fiducial marks: small registration marks exposed on the edges of a photograph. The distances between fiducial marks are precisely measured when a camera is calibrated, and this information is used by cartographers when compiling a topographic map.

Overlap: is the amount by which one photograph includes the area covered by another photograph, and is expressed as a percentage.

Stereoscopic Coverage: the three-dimensional view which results when two overlapping photos called a stereo pair , are viewed using a stereoscope. Crab During side winds, if the pilot tries to maintain the original path, he has to turn the nose of the aircraft slightly against the wind.

This makes the aircraft to rotate on its vertical axis. In this case, the original path is maintained, but the area covered by the aerial photo is much different from that planned originally. The photograph is rotated in the direction opposite to wind direction here. This defect is called as crab.

Crab occurs when the aircraft is not oriented with flightline. It causes a reduction in a stereoscopic coverage of the terrain. It can be corrected by rotating the camera around the vertical axis. Drift is the result of not be able the unmanned aircraft to keep the planned navigation bearing.