Aerial Remote Sensing Orientation of Camera Axis Vertical

Aerial Remote Sensing Orientation of Camera Axis Vertical and Oblique Photographs Angle of coverage and type of Photographs Films and its types Marginal Information of Aerial Photographs Dr R. Jegankumar. M. Sc. , M. Tech. , Ph. D. , Assistant Professor & Head Department of Geography School of Geosciences Bharathidasan University Tiruchirappalli – 620 024

v. Focal Length v. Flying Height v. Optical Axis / Nadir v. Angle of Coverage v. Field of View

Based on orientation of camera Ø Vertical aerial photograph Ø Oblique aerial photograph *low oblique *high oblique Vertical, high oblique and low oblique photograph of Goosenecks of the San Juan river in Utah

Vertical photograph § When the aerial camera axis is vertical or nearly vertical the resulting air photo is called as vertical photograph. § Allowable tolerance is usually +30 from the perpendicular line to the camera axis. Characteristics § The lens axis is perpendicular to the surface of the earth § It covers a relatively small area § The shape of the ground area covered in a single vertical photo closely approximates a square or rectangle § Distance and direction may approach the accuracy of maps takes one flat terrain § Relief is not readily apparent § The scale of the all points at the same level is uniform and the perspective almost resembles a map

• When an area is covered by vertical aerial photographs are taken along a series of parallel passes called flight strips. • The area covered by each successive photograph along a flight strip overlaps (60 -70%) part of the coverage of the previous photo. This lapping along the flight strip is called forward or longitudinal or end lap or fore or after lap • The area of coverage common to an adjacent pair of photograph in a flight strip is called the stereoscopic overlap area. • The pair of photos is called a stereo pair. • Adjacent flight strips are photographed so that there is also a lateral or overlapping of strips (25 -40%). This condition is called lateral or transverse or side lap. 60 -70% overlap 25 -40% overlap

§The vertical photograhs are largely being used for compiling topographic maps and for obtaining planimetric information on earth features such as crop acreage and other natural resources study §An unintentional and unavoidable inclination of the optical axis from the vertical produces a TILTED PHOTOGRAPH üVertical ØLow oblique ØHigh oblique

Camera orientation for various types aerial photographs Optical axis Camera lens Vertical Field of view Low oblique High oblique How a grid section lines appears on various types of photos Vertical photograph Low oblique photograph High oblique photograph

Oblique photographs When the camera axis is deliberately and intentionally inclined to the vertical or oblique, an oblique photograph is obtained. There are two types oblique photographs § Low oblique § High oblique

Low oblique photographs This is the photographs taken with the camera inclined about 300 from the vertical. It has the following characteristics • It covers relatively small area • The ground are covered is a trapezoid, although the photo is square or rectangular • The object have a more familiar view comparable to viewing from the top of a hill or tall building • No scale is applicable to the entire photographs and distance cannot be measured parallel lines on the ground is not parallel in these photographs there for the direction cannot be measured • Relief is discernible but distorted • It doesn't show the horizon

High oblique photographs is a photographs taken with the camera inclined about 600 from the vertical it is used primarily in the making of aeronautical charts. It has the following characteristics §It covers a very large area §The ground area covered is a trapezoid, but the photograph is square or rectangular. §The view varies from the very familiar to unfamiliar, depending up on the height at which the photograph is taken § distance and direction are not measured on this photograph §Relief may be quite discernible but distorted as in any oblique view §The horizon is always visible

Advantages of oblique photograph • • • Oblique photograph have an advantage in that one can take air photographs of an area without actually flying over that terrain. Other advantages are Greater coverage than vertical and hence less flying time More pictorial than vertical and hence more easily interpreted More used for publicity purposes, in real estate purposes Good for small scale mapping Useful in places of low relief, long coastline and minimum ground control

Based on angle of coverage The angle of coverage is defined as the angle. The diagonal of the negative format subtends at the near node of the lens of the apex of the cone of rays passing through the front nodal point of the lens. • • Narrow angle of photography Standard angle of photography Wide angle of photography Ultra wide or super wide angle of photography

Narrow angle of photography • The angle of coverage is of the order of 100 -200 • Format size 1) 18 cm *18 cm, f=610 mm 2) 23 cm*23 cm, f =915 mm • Used for intelligence, general interpretation and mosaics Standard angle photography • The angle of coverage is of the order of 500 -750 • Format size 1) 18 cm *18 cm, f=210 mm 2) 23 cm*23 cm, f =300 mm • Used for interpretation, mapping, colour photography and mosaics

Wide angle photography • The angle of coverage is of the order of 850 -950 • Format size 1) 18 cm *18 cm, f=115 mm 2) 23 cm*23 cm, f =153 mm • This is the most commonly used camera for mapping Ultra or super wide angle photography • The angle of coverage is of the order of 1100 -1300 • Format size 1) 18 cm *18 cm, f=70 mm 2) 23 cm*23 cm, f =88 mm • Used for mapping of areas with little relief

Based on lens • There are five main types of aerial photographs based on lens • Single lens photographs • Double or dual-strip photographs • Triple -strip photographs • Four lens photograph • Nine lens photographs

Single lens photographs • These are the most common cameras in use • They are extensively used in obtaining photographs for mapping purpose because they provide highest geometric picture quality • The lens is fixed relatively to the focal plane.

Double or dual-strip photographs • In the two cameras are mounted one on each side of the aircraft facing right to the direction of flight. Exposures made simultaneously with the cameras in this position result in dual strip photographs. • The axis of the camera is tilted outward by 5 -70 from the vertical. • By this method more area is covered. • Keeping the overlap of 60% longitudinally in the direction of flight.

Triple -strip photographs • Here three cameras are mounted , one is the centre pointing vertically downwards and two on each side of it. • The axis of the side camera given a tilt of 7 -100 to the vertical. So that the tilted strips just overlap the lateral edges of the vertical strip. • The advantages is that of large coverage of area in the case a dual strip camera is obtained.

Trimetrogen Photographs • This is an assemblage of three photographs taken at the same time, one vertical and two high obliques, in a direction at right angle to the line of flight.

Trimetrogen Photography 600 Ground Optic axis 10% side lap 10% Left oblique Coverage Central vertical coverage 60% Overlap Right Oblique coverage

Four lens photography • Used many years ago by the US soil conversion service , has a 10 by 10 inch overall picture size. • Each photograph is a composite of for individual exposures simultaneously with the camera system, in which four separate lenses are tilted and directed obliquely at the terrain • The tilt is essentially eliminated in processing and the four exposures are combined in to a single vertical equivalent view.

Nine Lens Camera • This is an unusual camera used by US coast and geodetic survey. • The central lens photographs the terrain directly beneath the aircraft, and the resulting photograph is a near vertical. • Each of the eight mirrors arranged around the periphery of the camera is inclined to the vertical at an angle of 190. The eight lens axis , although mounted parallel with the axis of the central lens are bend at the mirror, so that each one makes an angle of 380 with the vertical. All eight peripheral photographs are therefore low oblique. • The total angular coverage of the nine lenses 130 by 130. Each lens has a focal length 20. 93 cm(8. 24 inches). • The camera assemble contains the total of 45 fiducial marks. These are necessary to orient each of the separate negative in the transformer pointer when the composite photograph is made.

Marginal Information of Aerial Photographs Annotations 1. Fiducial marks. 2. Date of photography. 3. Verticality level. 4. Time 5. Flying height (in feet). 6. Altimeter. 7. Focal length. 8. Task number. 9. Flying- agency. 10. Run / path number. 11. Exposure number. 12. Photo number.