![Side Lap gain
Side lap gain, the distance between the centers
of adjacent flight lines and calculated by using
following equation:
Gside = Sp x W [(100 – Oside)/100]
Where
Gside= distance between flight line centers (feet)
Sp = photo scale denominator
Oside= side lap (percent)
W = width of the exposure frame (inches or
cms).](https://image.slidesharecdn.com/3planning-230521150645-1deb7f54/85/3-PLANNING-ppt-31-320.jpg)
3, PLANNING.ppt
- 5. Displacement and errors In photography survey we try to represent 3 D surfaces of the earth as 2D image Object appear in photograph are geometrically distorted, known as relief displacement. Reasons for distortion Movement of camera Instability of aircraft Variation in altitude, tilt and speed Curvature of earth Rotation of the earth Spring 1998 Field Geography
- 7. Crab Opposite lines of photographs are not parallel to flight line is Known as Crab of photograph. Spring 1998 Field Geography
- 9. Drift When aircraft is swayed away from its preplanned flight line then it is known as Drift Usually coursed by wind spirits Spring 1998 Field Geography
- 12. PLANNING FOR AERIAL PHOTOGRAPHY Successful execution of any photogrammetric project requires thorough planning prior to proceeding with the work. Planning, must be done by knowledgeable and experienced persons. One of the most important considerations that must be addressed in planning the decision of exactly what products will be prepared, with their scales and accuracies.
- 13. Elements of planning Spring 1998 Field Geography 1. purpose of photogrammetry Wide angle photograph (152mm focal length) is required for topographic mapping If area is highly wooded us f= 210 mm( standard angle) to allow more visibility through trees Generally 60% overlap with 15% side lap
- 14. 2 photo scale Spring 1998 Field Geography It depend on the accuracy level work Type of the purpose of the photograph. Some what depend on type of plotter
- 15. 3. Relief displacement Spring 1998 Field Geography Relief displacement decrease as flight high increase Flight high increase as relief displacement decrease.
- 16. 4. Tilt Spring 1998 Field Geography Will cause overlap will be greater on one end than other Will increase side lap on one side and decrease on other
- 17. 5. Crab and drift Spring 1998 Field Geography Crab- angle formed b/n flight line and edges of photo Drift error- Plane which is not stay on flight line. Commonly coursed re-flight and gaps
- 18. 6. Flying height Spring 1998 Field Geography Determined after side lap and overlap Factors affecting 1. scale, relief displacement, and tilt 2. precision of equipment used Greater precision grater possibility flight height 7. direction and orientation of the terrain Arrange to fly along ridge not across
- 19. Project planning Spring 1998 Field Geography Successful execution of any photogrammetric project requires thorough planning Must first determine the selection of products to be prepared their scales and accuracies of areal photo, plan metric map, Cadastral map, Digital elevation map (DEM).
- 20. flight planning Spring 1998 Field Geography Success of photogrammetry project depend on acquisition of good quality pictures Due to weather and ground condition, time frame for photograph is limited Refight are expensive and cause long delay on project Mission must be carefully planned and executed according to flight plane where photo should be taken and specifications
- 21. Specifications Spring 1998 Field Geography Camera requirement Film requirement Scale Flying height End lap, and side lap Tilt and crab tolerance
- 23. Direction of flight lines Spring 1998 Field Geography
- 24. Weather conditions Spring 1998 Field Geography Flight crew should interpret weather condition and make sound decision on whether to fly or not fly Ideally cloud free < 10% cloud cover acceptable Cloud higher than the flight high might cause large shadow on the ground. Photos for industrial areas susceptible to atmospheric haze, smog, dust, and smoke are taken after heavy rains High wind motion will difficulty in camera and aircraft ordination.
- 26. Photo scale Average photographic scale is one of the most important variables that must be selected in planning Aerial photographs. Photo scale is determined by knowing the focal length of the camera and flight height. Sp = f / H If average ground elevation is considered then, Sp = f" / (H'-h')
- 27. Flying Height Once camera focal length and required average photo scale have been selected, required flying height above average ground is fixed in accordance with the scale. The flying height of the camera depends on the scale of the photograph. The Aerial photograph scale depends also on the topography or changes in elevation. Actual Flight Height = Flight Height + MSL
- 28. Overlaps The overlap of photographs in the direction of flight line is called forwarded overlap or End Lap. A minimum of 55% to 65% with an average of 60% is maintained while running a flight. The overlap between adjacent flight lines is known as Side Lap. The side lap is maintained between 20% to 35% with an average of 30%.
- 29. End Lap gain: End lap gain, the distance between the centers of the consecutive photographs along a flight path, it can be calculated by using a formula Gend = Sp x W (100-Oend)/100 Where; Gend = distance between exposure station Sp = photo scale denominator Oend = side lap (percent) W = width of the exposure frame (inches or cms).
- 30. Cont… Send = photo scale denominator Oend = end lap (%) W = width of exposure frame (inch or cm).
- 31. Side Lap gain Side lap gain, the distance between the centers of adjacent flight lines and calculated by using following equation: Gside = Sp x W [(100 – Oside)/100] Where Gside= distance between flight line centers (feet) Sp = photo scale denominator Oside= side lap (percent) W = width of the exposure frame (inches or cms).
- 32. Cont…
- 33. Calculation of Number of strips and photographs for a specified area. For a complete aerial survey a complete photographic coverage with requisite overlaps is required. Once the sale of photo is decided the time interval for successive exposure can be calculate considering the velocity of aircraft. Strips are spaced at calculated distances to ensure the required side overlap between the adjacent flights.
- 34. a) Total area of project site = L x W b) No of flight line required to cover the site area = Total width / Side lap gain c) No. of photo per line = Line length /End Lap gain +1 d) Total No. of photos = No of flight line x No of photo per line e) Time interval for successive exposure can be calculated considering the velocity of aircraft
- 35. e.g. if the photo size is 23cm x 23cm, the overlap is 60%, scale of photo is 1:25,000 and speed of plane is 360 km/h. Find the time interval for successive exposure. Solution End Lap gain = Sp x W (100-end)/100 =25,000 x 23 x 40/100 = 230000 cm = 2300m. Speed of aero plane = 360km/hr = 360x1000/60x60 =1000 m/s. Time interval = End Lap gain /Spaced of plane 2300m/100m/sec = 2.3sec.
- 36. Flight Planning for Aerial Photography We have a study area over Bahir dar town, 30 km wide in east to west direction and 15 km along in the north – south direction Camera focal length 152.4 mm focal length, and the sine size is 230 mm( 9*9( format is used) The required scale is 1: 20,000 and the end lap and side lap is 40 % and 20% respectively. The plane speed is 300km/h Spring 1998 Field Geography
- 37. Your assignment calculate each question 4 mark Flight direction Flight height Ground coverage per sine or exposure Over lap and side lap If plane speed is 300 km/h calculate time b/n exposure No of line No of photo Note;- each question is with brief explanation and brief procedure.
- 38. End of lecture Read, Read again read