Determination of Flight Direction

about the flight direction determined by the aerial photography methods

1. Determination OF FLIGHT DIRECTION

2. Introduction The term “Photography” is derived from two Greek words meaning “ phos ”(light) and “ graphien ” (writing) Photography is the production of permanent images by means of action of the light Aerial Photography is broadly defined as any photographs of that takes place from an elevated position.

3. Many factors determine the quality of aerial photography Quality of the lens system Manufacturing the camera Photographic material Weather conditions and sun angel during photo flight

4. Classification of Aerial photograph Aerial photographs are usually classified according to the orientation of the camera axis, the focal length of the camera There are 3 types * Horizontal photography * Vertical photography *Oblique photography

5. Annotations Fiducial marks * these are the marks built into aerial cameras which appear on the sides or in the corners of the photo * these are used to determine the precise location of the principal point

6. Fiducial axes The lines joining the opposite fiducial marks on a photograph are called fiducial axes. Principal point It is a point on the aerial photograph, where a perpendicular from the interior perspective centre of the camera lens meets the plane of the aerial photograph The principal point is the geometric centre of the photograph

7. XY co-ordinate: they are obtained by joining opposite fiducial imaginary X co-ordinate and Y co-ordinates. Perspective centre: It is the centre point of the lens in camera. Flight line: Photographs are taken with the frame of the cameras along one line. These lines are called flight line.

8. Conjugate Principal point It is a principle point of an aerial photo represented on an adjacent aerial photograph.

9. Nadir Point Nadir point is the point in which a vertical line through the perspective centre of the camera lens pierces the plane of the aerial photograph.

10. Photo-base The airbase is called the photo-base on an aerial photograph and represents the length of the air-base on a photograph. In practice it is measurable distance between the principal point and the conjugate point

11. Preparation of flight to acquire aerial photographs process begins with selecting an image scale, camera lens and format size, and desired image overlap. flight planner can then determine such geometric factors as the appropriate flying height, the distance between image centres, the direction and spacing of flight line, and the number of images required to cover the study area. Based on these factors, a flight maps are prepared for the firm providing the photographic services.

12. Determination of flight direction

13. procedure Demarcate the boundary of stereopair. Demarcate the symbols like fiducial marks, scale etc. Join opposite fiducial marks to get co-ordinates. X and Y co-ordinates meet the centre and meeting point is called principal point.

14. Principal point of first photograph will be present on second photograph called conjugate principal point. Maximum number of points will be present due to 40% - 60% overlap. By finding or tracing common points, we can determine the flight direction.

15. conclusion Before the aerial photographs came into practice for analytical and computational work, similar data collection for topographical surveys and geological investigations used to be various photogrammetric and photo-interpretation techniques, the same work is being carried out more precisely with economy of time, money and efforts.

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