Correcting Lens Dependent Aberrations

Gully Erosion Morocco

Lens-dependent aberrations are circular effects centered on the optical center of the image. Therefore, it is important to correct them before cropping or warping the image. Many photo-editing software packages and some modules of professional remote sensing software include tools for correcting vignetting, CA, and sometimes even lens distortion. The degree of vignetting depends on lens characteristics, aperture, and exposure and is thus not an invariable effect it is difficult to correct...

Contrast Enhancement

Most aerial photography covered in this book shows landscapes of all sorts, and few of them abound in striking colors with lively contrasts. Even more than high-oblique images, vertical aerial photographs for geoscientific applications tend to be restricted to shades of green, brown, and beige. Yet exactly the subtle differences in color shades may be interesting for distinguishing certain soil properties or vegetation types. Various ways exist for manipulating the distribution of tones across...

Powered Light Sport Aircraft

LSA are supplied nowadays mainly by small companies. The relatively low costs of purchasing, building, and operating manned LSA have proven popular. One suitable model, for example, is the Challenger II produced by Quad City Challenger of Moline, Illinois, United States. It is a two-seat LSA and ultralight trainer with an overhead wing and pusher motor (Fig. 8-1). The long-wing version increases the glide ratio and is the optimum configuration for stable, slow-speed SFAP. Wheeled or float...

Image Enhancement

SFAP images for scientific applications are taken usually with the intention to show certain information about a site or an area thus, optimizing the visual interpretability of an image with image enhancement techniques is often the primary concern. As discussed in Chapter 6.4.6, photographs taken with small-format cameras are not without radiometric deficiencies. Image-degrading effects like chromatic aberration (CA), vignetting, and noise can be corrected partly or completely with camera...

Photography And Imagery

The word photograph means literally something written by light,'' in other words an image created from light. For the first century of its existence, photography referred exclusively to images made using the light-sensitive reaction of silver halide crystals, which undergo a chemical change when exposed to near-ultraviolet, visible, or near-infrared radiation. This photochemical change can be developed into a visible picture. All types of film are based on this phenomenon. Beginning in the...

Flight Planning For Oblique Sfap

Flight planning for oblique aerial photography is rarely done to achieve overlapping images for mosaics or stereoimagery, as detailed in previous sections. Rather the oblique vantage is chosen to depict the spatial relationships of objects and features within the landscape in a more pictorial fashion. The geometric distortions of single-point perspective, relief displacement, and scale variations are accepted, and the FIGURE 9-17 High-oblique view northward over the Elk River Wind Farm in the...

Image Rectification

Basically, three different types of distortion may be present in an SFAP image lens distortion, image tilt, and relief displacement see Chapter 3.2 . Two methods of correcting these errors, polynomial rectification by ground control points GCPs and orthorectification, have already been introduced in Chapter 3.4.1. Also, the precision and survey methods for GCPs have been discussed in Chapters 3 and 9. The following sections look at some exemplary questions and cases related to geocorrecting...

Pattern and Texture

Pattern refers to the arrangement of discrete objects, which individually are visible distinctly and form some regular arrangement with each other, for example vehicles in a parking lot, fruit trees in an orchard, crop rows, or FIGURE 5-5 Strong diagonal elements may be utilized for visual emphasis. Fall River Lake, southeastern Kansas, United States. A Overview of dam and roads. B Closeup view of dam and spillway. Kite aerial photographs by JSA, June 2006. FIGURE 5-5 Strong diagonal elements...

Basic Elements Of Photographic Composition

Photographic composition begins with color or gray tones it is through color variations that we see and interpret what is present in the picture. The visible objects in the scene are further defined based on their sizes, shapes, patterns, textures, and contrast with each other. Additional visual elements include the relative placement and balance between objects in the picture. Photographic composition has much in common with landscape painting, and many general guidelines have been elaborated...

Hot Air Blimp

Tethered Mode Balloons

Spherical hot-air balloons experience the same stability problems as helium balloons. If they are free flying, they are simply uncontrollable, and in tethered mode they start turning erratically even at quite low wind velocities. In addition, the internal pressure inside the hot-air balloon needs to be FIGURE 8-14 Urban, industrial scene, Kansas City, Kansas, United States. Missouri River on right side. Blimp was launched from a small park next to the river. Taken from Aber and Aber 2009, fig....

Camera Operation

The main tasks of the mount are holding and operating the camera. The solutions to the latter may be as basic as a onetime mechanical trigger that has to be reset manually before each exposure Fig. 7-1A, B , but in times of electricity and remote-control devices, repeated triggering via radio-controlled microservos Fig. 7-1C or electronic shutter release cables see below is the established standard. Many recent camera models mostly digital single-lens reflex DSLR cameras that support the...

Helium Blimp

The small helium blimp used by one of us is 4 m long and has a gas capacity of 7m Aber, 2004 . The blimp has a classic aerodynamic shape with four rigid fins for stability in flight. It has a payload lift of 3 kg, which is 2-3 times the weight of camera rigs and has proven to be an adequate margin of safety for blimp operation. The camera rig, which is the same system utilized for kite aerial photography KAP see Chapter 7 , is attached to a keel along the bottom of the FIGURE 8-10 Small gas...

Camera Geometry And Light

A geometric relationship exists between the lens focal length, image format, area angle of view, and the amount of light that reaches the film or electronic sensor. Some common lens focal lengths are given in Table 6-2. Many cameras are now equipped with zoom lenses that allow the user to vary the focal length. The lens aperture and shutter speed are fundamental controls for how much light reaches the film or image sensor. Film speed or ISO rating determines how much light is required for...

Latitude And Seasonal Conditions

The position of the sun is a critical factor for controlling the amount and quality of light available to illuminate the Earth's surface. Latitude, day of year, and time of day determine where the sun would be located for any site. The normal expectation of toplighting for small-format aerial photography means the sun should be relatively high in the sky to avoid excessive shadowing of the landscape, and a further criterion is usually cloud-free sky for best illumination of the ground. This...

GCP Installation

Photogrammetric Gcp Sample

As discussed in Chapter 3, a theoretical minimum of three GCPs is necessary for adjusting an image to a reference coordinate system. In reality, more GCPs are necessary to cover an area with differing elevations well enough for georeferencing and to ensure that sufficient GCPs appear on each photograph see Chapter 11.2 . For more advanced photogrammetric analysis, a surplus of GCPs is advisable which can be used as check points and enable error assessment of digital elevation models DEMs...

Autopiloted Model Airplane

Pilot-operated model airplanes, as shown by the previous example, are not the easiest platform for SFAP. They require considerable flying experience of the pilot to start with, and even more experience and technical skills for pin-pointing exact locations with vertical photographs or covering large areas in systematic flightline arrangements. Recent developments in global positioning system GPS and inertial FIGURE 8-38 Close-up view of the Multiplex Easy Star model airplane in the field with...

Image Interpretability

Visual identification of objects in vertical airphotos normally requires ground sample distance GSD 3-5 times smaller than the object itself Hall, 1997 , as noted before Chapter 2 . For example, to positively identify a house 10 m x 10 m , the camera image system needs to achieve a GSD in the range of 2-3 m. Factors other than spatial resolution often affect the ability to recognize objects, however. Contrasts in color and brightness are important clues as are size, shape, context, shadows, and...

Water and Drainage

Gimp Erosion Terrain

Water is the most widespread feature on the surface of the Earth, and water bodies exist in many forms seas, lakes, rivers, ponds, estuaries, bayous, lagoons, etc. In aerial FIGURE 10-2 Vertical SFAP of a pond with emergent leaves of the American lotus Nelumbo lutea . Individual leaves are clearly visible around the margin of the pond these leaves are typically about one foot 30 cm in diameter. The dock is 15.5 m long. GSD for the original image is 5cm, and the NIIRS rating is 8. Kite aerial...

Single Camera Suspended Rigs

Picavet Rig Servo

Most single-camera mounting systems for kite or blimp aerial photography include the basic functions for camera position pan and tilt and shutter trigger, which are usually controlled by radio from the ground. In this relatively simple approach, no video downlink or other onboard equipment is involved in the mounting system. The camera position pan and tilt is estimated by visual observation of the camera from the ground, usually with binoculars, and by radio-control settings. Many pictures are...

Kites for SFAP

Kite Flowform Cartoon

Many types of kites may be employed, but no single kite is optimum for KAP under all circumstances. Various kites are utilized depending on wind conditions and weight of the camera rig. The goal is to provide enough lift to support the payload normally ranging from 1 to 3 kg. For a given camera rig, large kites are flown for lighter wind and smaller kites for stronger wind. Kite designs fall in two general categories. Soft kites have no rigid structure or support to maintain their shape. The...

Fixed Mounts

Suspended or semi-fixed mounts are not suitable for free-flying, aerodynamic SFAP platforms if they jeopardize the stability of the platform, swing with the platform movements, or take too much room. The autopiloted model airplane and the paraglider see Chapter 8 feature fixed mounts, because they fly too fast for suspended rigs. Also, a modular plug-in mount would not make sense for free-flying platforms, as it could not be attached after launching. Two problems need to be addressed for...

Clouds

Clouds play a critical role for effective small-format aerial photography. The nature and optical properties of clouds vary enormously from high, thin cirrus clouds of ice crystals to dense ground fog. In addition to ice and or water droplets, clouds may consist of dust, smoke, and other minute debris in the atmosphere, which are derived from both natural and human sources. The particles of clouds range in size from lt 1 mm diameter to a maximum of 100 mm. Clouds are intrinsically white, as...

Multiple Camera Suspended Rigs

Camera Mounting Systems

For some purposes, a single camera is not enough. Dual- or even multiple-camera mounts may be used for simultaneous images either in various spectral ranges, with different focal lengths image scales, or from different vantage points for stereo imagery. Multiple-sensor mounts also may combine cameras with such non-imaging spectral measurement devices as spectroradiometers or thermal-infrared sensors in order to collect multispectral information about the viewing target e.g. Vierling et al.,...

Drones For Sfap

Hexakopter Uav Frame Nederland

Drones also called UAVs or MAVs are unmanned, powered, free-flying platforms that vary greatly in their technical characteristics and photographic capabilities. They may be controlled by a pilot on the ground, who is in visual contact with the drone, or they may be FIGURE 8-34 JSA demonstrates a mobile anchor for the kite reel and line. The reel is attached to a harness around the waist and hips of the kite flyer. A small two-way radio on left arm allows communication with the camera operator...

Attaching Suspendable Mounts to a Platform

Attach Camera Kite Line

Suspendable camera mounts are connected to the platform via lines or poles that are free to swing, pivot, or flex, so that the camera is removed to some extent from erratic motions and vibrations of the lifting platform. Ideally the mounting system should hang in a stable, level position. Two different solutions are the pendulum and Picavet suspensions. Both may be combined with a cable-car system in kite aerial photography, or directly attached to a kite line or to a balloon or blimp envelope....

Image Degradation

Photographs do not record the energy reflected off their motifs flawlessly. Chemical and physical characteristics of films and image sensors may introduce unwanted effects and artifacts into an image. Also, the lens is crucial for image quality, and some degree of distortion always is introduced into the optical paths by deviations from a perfect central perspective. The most frequent types of distortions and artifacts are briefly described in the following see Chapter 11 Radial distortion...

Ideal Flightline Calculation

Following these conclusions, it remains to be calculated which exposure interval would be necessary if a free-flying platform, specifically the autopiloted model airplane presented in Chapter 8.5.2, is used for continuous flightline coverage, and if this interval is feasible with the chosen camera. Taking into account that in windy conditions the airplane might not yield a perfectly aligned image series, a 70 forward overlap is considered as minimum. FIGURE 9-16 Aerial photograph of Gully...

Stereoscopic Images

Jan Ostermann Sfap

Humans see in three dimensions, in other words, we have depth perception, because our eyes provide overlapping fields of view from slightly different vantage points. The amount of depth perception in humans is limited to about 400 m distance, however, because of the relatively close spacing of our eyes, i.e., only 6-7 cm apart Drury, 1987 . Stereoscopic photography has been practiced since the middle 19th century to provide 3-D imagery Osterman, 2007 Fig. 2-8 . Aerial stereo photographs may be...

Camera Calibration

Camera calibration see Chapter 3 significantly improves the accuracy of photogrammetric analyses. Chandler et al. 2005 found that radial lens distortion errors effectively constrain the accuracies achievable, making accurate modelling of lens distortion an important issue for the use of consumer-grade digital cameras. Investigations into the temporal stability of a digital compact camera by Wackrow et al. 2007 confirmed the relative importance of inaccurate lens distortion parameters as...

Combining Compositional Elements

Aerial View Circular Fountain

The combination of multiple visual elements creates the most dramatic photographs from an aesthetic point of view. The concept of compositional balance refers to the placement and relative visual impact of objects in the picture Wildi, 2006 . Most pictures consist of a main subject and secondary subjects arranged within a less conspicuous background. In general, the main subject should not be located at the geometric center of the photograph. The main subject should be offset toward the top,...

Colorinfrared Photography

Nir Adapted Powershot

Color-infrared film is sensitive to visible and NIR portions of the spectrum. In normal practice, a yellow filter is employed to eliminate blue and UV wavelengths. In some cases, orange or red filters may be used to further restrict visible light from reaching the film. Color-infrared film carries no ISO number nor do conventional light meters provide correct indications of NIR radiation. Without an ISO bar code on the film case, most cameras cannot make automatic settings. Therefore, taking...

Photographic Storage

SFAP is more than just snapshots usually the images are intended for long-term storage and reproduction years and even decades after they were acquired. However, neither film nor digital photography is everlasting all photographic media are subject to long-term decay Rosenthaler, 2007 . Thus, proper storage of the images becomes a significant issue for most SFAP projects. Geographic information typically consists of two kinds of data. First is the primary dataset composed of location...

Multiviewangle Effects

Azimuthal Aerial Photo Alamy Com

Multiview-angle effects are everywhere. Consider a newly mowed lawn or harvested crop field. Distinct stripes are visible both on the ground and from the aerial vantage Fig. 4-3 . These stripes reflect passage of the mower back and forth across the field such that the grass or crop stubble is bent at opposed angles for alternate stripes. As this example demonstrates, multiangular reflectance is a basic property of the natural world, and this has many implications for small-format aerial...

Shadows

The issue of shadowing in an image is obviously strongly connected to the latitude, time of day, and cloud aspects discussed above. With direct illumination by the sun, all three-dimensional objects or surface features cast a shadow if they project into the paths of the light rays between sun and ground. Shadowing in aerial images is most prominent at early morning and later afternoon and increases with higher latitudes. The darkening effect of shadowing increases with longer wavelengths as...

Photographic Scale and Resolution

The scale of a vertical aerial photograph can be calculated simply in two ways. The scale S depends on the average height above the ground Hg and the lens focal length f of the camera. In either case, the units of measurement must be the same. S photo distance d ground distance D In cases where objects of known size appear in the vertical photograph, the first method may be utilized for scale calculation Fig. 2-3 . If no objects of known size are visible in the photograph and the flying height...

Multispectral Effects

Artificial Turf Spectral Reflectance

As humans, we view the world through a narrow range of electromagnetic radiation, the visible spectrum 0.40.7 mm wavelength see Fig. 2-1 . Film photography extends this range from near-ultraviolet to near-infrared 0.3-0.9 mm . Black-and-white infrared film was developed in the 1920s and was utilized for aerial photography already in the 1930s Colwell, 1997 . World War II spurred a great need for aerial camouflage detection, and color-infrared CIR film was perfected. Nowadays both CIR film and...

Manual Measuring and Mapping from Stereomodels

Stereo Aerial Photography Images

In a single image, the location of a point is given by its position x, y. Its corresponding 2D object space coordinate X, Y can be determined by some method of georeferencing as described above. when measuring from stereo images that have been relatively and absolutely oriented in a ground coordinate system, the stereoscopic parallax of a point is measured additionally for deriving its height Z. All stereoscopic measurement devices analog parallax bars for stereoscopes, analytical...

Bidirectional Reflectance Distribution Function

The Parabola Iii Brdf

Qualitative variations in scene brightness and contrast depending on viewing angle and sun position are commonplace in small-format aerial photography, as noted above. The goal of the bidirectional reflectance distribution function BRDF is to model these variations quantitatively Lucht, 2004 . The BRDF is based on viewing and illumination angles as well as complex geometrical and optical properties of objects in the target scene. Considerable effort has been made to understand BRDF better for...

Tilted Photography

True Vertical Photograph

None of the equations given above is valid for oblique photographs with non-vertical optical axes, because the scale varies with the magnitude and angular orientation of the tilt Fig. 3-3 . The magnitude of the tilt is expressed by the nadir angle v, which is the angle between the optical axis and the vertical line through the perspective center nadir line and is the complement of depression angle. Topographic relief introduces additional scale variations and radial distortions relative to the...

Vertical Photography

Relief Displacement Principal Point

Other than a map and similar to the images we perceive with our eyes, a photograph either analog or digital is the result of a central projection, also known as singlepoint perspective. The distances of the central point of convergence the optical center of the camera lens, or exposure station to the sensor on one side and the object on the other side determine the most basic property of an image, namely its scale. Figure 3-1 shows the ideal case of a vertical photograph taken with perfect...

Nineteenth Century

Types Aerial Photographs

Louis-Jacques-Mande Daguerre invented photography based on silver-coated copper plates in the 1830s, and this process was published by the French government in 1839 FIGURE 1-4 Bird's-eye view of Niagara Falls, Canada, and the United States. George Catlin, 1827, gouache, 45 x 39 cm. Adapted from Dippie et al. 2002, p. 36 . FIGURE 1-4 Bird's-eye view of Niagara Falls, Canada, and the United States. George Catlin, 1827, gouache, 45 x 39 cm. Adapted from Dippie et al. 2002, p. 36 . Romer, 2007 ....

Baseheight Ratio and Stereoscopic Coverage

Focal Length And Aerial Photographs

From Figure 3-6 it is also evident that the stereoscopic parallax p and thus depth impression can be increased when the eye base B is increased, an option we do not have in reallife viewing, but is possible and desirable in artificial stereoscopic viewing. If the base between the exposure stations in relation to their height the photographic base-height ratio is larger than the base of our eyes in relation to the viewing distance the stereoviewing base-height ratio , the stereomodel appears...

Measuring and Mapping from Single Photographs

Individual measurements of lengths and sizes the width of a brook, the diameter of a tree crown, the distance between vegetation patches can be taken easily in analog or digital photographs using Equation 3-1, if the image shows an object or distance with known length. This could, for example, be a scale bar as in Figure 2-3 or the calculable distance between two ground control points as in Figure 9-8. Adapting Equation 3-1, the required ground measure D can be calculated by comparing its image...

Automatic DEM Extraction from Stereomodels

A digital elevation model DEM is a digital representation of terrain heights. The most common forms are a regular grid usually saved in raster format or a triangular irregular network TIN of triangle facets vector format . They can be created by manual collection see preceding section of height points, breaklines, and contours and subsequent application of interpolation algorithms or Delaunay triangulation, which convert these data to regular grids or TINs Li, Zhu and Gold, 2005 . With the...

Measurements from Stereomodels

Aerial Stereopair Photografs

Beyond the simple viewing and interpreting of stereopairs, stereomodels also enable various kinds of 3D measurements using photogrammetric techniques. The 3D ground FIGURE 3-11 Two stereopairs with equal image scale and air base B taken over the same terrain. Focal length and flying height of stereopair B normalangle lens are twice those of stereopair A wide-angle lens , resulting in a halved base-height ratio. Note how the parallactic angles g and the stereo-parallax the difference between and...

Creating Stereomodels with Aerial Triangulation by Bundle Block Adjustment

Aerial Triangulation

In praxis, photogrammetric analysis is mostly done using not one, but several or even many stereopairs for covering larger areas. In order to avoid the individual orientation of each stereomodel with accordingly large numbers of ground control points, multiple overlapping images forming a so-called block see Fig. 3-8 and 3-9 can be oriented simultaneously with fewer ground control points using aerial triangulation techniques. One of the most commonly used and most rigorous aerial triangulation...

Conventional Aerial Photography

Since World War I, aerial photography has evolved in two directions, larger formats for accurate mapping and cartographic purposes and smaller formats for reconnaissance usage Warner et al., 1996 . The former became standardized with large, geometrically precise cameras designed for resource mapping and military use. The science of photo-grammetry was developed for transforming airphotos into accurate cartographic measurements and maps Wolf and Dewitt, 2000 . Standard, analog aerial photography...

Twentieth Century

Aarhus Aerial Photography

The early 20th century may be considered the golden age of kite aerial photography. At the beginning of the century, kites were the most widely available means for lifting a camera into the sky. Aerial photographs had been taken from balloons since the mid-1800s, but balloon aerial photography was a costly and highly dangerous undertaking and so was not widely practiced. Meanwhile powered flight in airplanes had just begun, but it also was quite a risky way to take aerial photographs. Kites...

Sfap

Small-format aerial photography is based on lightweight cameras with 35- or 70-mm film format as well as equivalent digital cameras and other electronic imaging devices. For the most part, these are popular cameras designed for hand-held or tripod use by amateur and professional photographers. Such cameras lack the geometric fidelity and exceptional spatial resolution of aerial mapping cameras. However, the case for SFAP depends on cost and accessibility. Low cost SFAP cameras are relatively...

Overview

People have acquired aerial photographs ever since the means have existed to lift cameras above the Earth's surface, beginning in the mid-19th century. Human desire to see the Earth as the birds do'' is strong for many practical and aesthetic reasons. From rather limited use in the 19th century, the scope and technical means of aerial photography expanded throughout the 20th century. The technique is now utilized for all manners of earth-resource applications from small and simple to large and...

Preface

Photography has the remarkable power to impress into memory a distillation of a particular segment of time. L. Schwarm Schwarm and Adams, 2003 Why small-format aerial photography This question is often posed to us by people who work on the ground as well as those who analyze conventional aerial photographs and satellite images. Why indeed The authors did not start their small-format aerial photography SFAP careers as dedicated kite flyers, hot-air blimp developers, UAV fans, or do-it-yourself...