Drones For Sfap
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
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...
Summary Efv
Small-format aerial photographs typically are taken under clear sky when the sun is relatively high to provide for good toplighting of the Earth's surface, although uniformly indirect lightning from high clouds or overcast sky is preferable in some situations. The position of the camera relative to the ground and sun plays a key role for determining the nature of reflected solar radiation reaching the camera. Anisotropic variations in reflectivity, depending on sun position and angle of...
Introduction Cxr
A successful small-format aerial photography SFAP field survey often depends on the ability to react flexibly to a plethora of complications the more of these that can be anticipated and planned for in advance, the more likely one would return with plenty of good images. SFAP can be undertaken quickly and spontaneously, for example, with a lightweight minimal kite system for an afternoon leisure hour at the beach to capture a bird's-eye view of that spectacular cliff above the churning...
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
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
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
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...
Film Speed or ISO Rating
Different photographic emulsions on film vary greatly in their sensitivity to light some require little, others need much light to properly record an image. This factor is known as film speed, which is indicated by a standard ISO rating. Low ISO values indicate slow films that need much light. High ISO values, in contrast, are typical of fast films that require little light. The latter have larger silver halide crystals in the emulsion, which tend to give a grainy structure to the image....
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FIGURE 5-13 Schematic illustration of the Munsell Color system. A Wheel arrangement of hue, value, and chroma. B Wedge representing the purple hue section of the wheel. Adapted from GSA Rock-Color Chart 1991 . nature, that people are attracted to autumn foliage, painted-desert scenes, flower gardens, and similar bright, warm colors Fig. 5-15 . In fact, hot and cold colors induce a pseudo depth perception hot colors appear closer and cold colors seem farther away from the viewer Eyton, 1990...
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...
reenrednearinfrared
FIGURE 4-19 Anisotropy factors for three wavelengths measured in perennial ryegrass with a field goniometer. Red displays the strongest BRDF, green is intermediate, and near-infrared is weakest. Adapted from Sandmeier 2004, fig. 3-3 . FIGURE 4-19 Anisotropy factors for three wavelengths measured in perennial ryegrass with a field goniometer. Red displays the strongest BRDF, green is intermediate, and near-infrared is weakest. Adapted from Sandmeier 2004, fig. 3-3 . shadowed zones. Thus, CIR...
Multiviewangle Effects
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
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
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
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
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
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
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 ....
Introduction
Photogrammetry is the art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting photographic images and patterns of recorded radiant electromagnetic energy and other phenomena Wolf and Dewitt, 2000 McGlone, 2004 . Photogrammetry is nearly as old as photography itself. Since its development approximately 150 years ago, photogrammetry has moved from a purely analog, optical-mechanical...
Baseheight Ratio and Stereoscopic Coverage
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...
D Measurements from Stereomodels
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 BundleBlock Adjustment
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...
Relief Displacement
The camera lens operates much like the human eye, both of which produce single-point perspective views of the scene. This perspective produces increasing relief displacement of objects nearing the edge of view. This is most noticeable in vertical airphotos, because tall objects appear to lean away from the photo center. Conversely, low objects are displaced toward the center. Relief displacement is minimal near the photo center and becomes extreme at the edge. This allows for a side view of...
Twentieth Century
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...
Brief History
Since ancient times, people have yearned to see the landscape as the birds do, and artists have depicted scenes of the Earth as they imagined from above. Early maps of major cities often were presented as bird's-eye views, showing streets, buildings, and indeed people from a perspective that only could be imagined by the artist. Good examples can be found in Frans Hogenberg's Civitates Orbis Terrarum Cologne, 1572-1617 . Seventeenth-century artists such as Wenceslaus Hollar engraved remarkable...
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...