- SPECIAL REPORTS
- THE MAGAZINE
I think back to the technology in place in the early 1990s and the changes that have occurred in the 10 years since then. Film cameras with forward motion compensation (FMC) were just beginning to be accepted by larger aerial firms; GPS was declared fully operational by the Department of Defense in firms; airborne GPS (ABGPS) control procedures were being pioneered, flight management systems were coming online, LiDAR acquisition in an airborne platform was still a dream and digital cameras for mapping uses were only on the drawing board. The Manual of Aerial Survey was first published in 1986, but in the recent much-revised edition the authors were able to include useful information regarding each of these new and important topics.
Authors Read and Graham state, "the subject is covered with a minimum of mathematics and the information is readily accessible whether the book is read in full or consulted for a particular topic." By accomplishing this objective, they have created a text that is useful for a wide audience. Photos and illustrations throughout the book effectively reinforce the text, a critical element to improve the readability for anyone not involved in the day-to-day operations of imagery acquisition.
Aerial AcquisitionThe first few chapters of the book provide an informative discussion of the historical background including the early days of photography as well as mapping developments arising from military applications. Also included is a thorough discussion of the terms and definitions that apply to the subject.
The real meat of the text, however, begins in the third chapter titled "Air Camera Instrumentation." This chapter provides a detailed discussion of each of the main film camera options used by aerial acquisition firms today. These include the Leica Geosystems RC-20 and RC-30 (Leica Geosystems, Atlanta, Ga.); Carl Zeiss (Jena) LMK 1000, LMK 2000 and LMK 3000 (Carl Zeiss, Thornwood, N.Y.); and Z/I Imaging RMK Top (Z/I Imaging, Huntsville, Ala.). All of these precision cameras are equipped with FMC, and therefore a discussion, albeit brief, of this technology and its importance in acquiring quality imagery is included.
There is only slight mention of the Z/I T-Flight and Leica ASCOT flight management systems, an area where more information would be welcomed. Flight management systems are used in virtually every aerial acquisition platform today. Their integration with imagery acquisition is one of the most significant advances in precision photo collection over the last decade and arguably almost solely responsible for the near elimination of reflights due to missed project coverage or inadequate overlap. Additionally, flight management systems offer a great demonstration of hardware and software technology and would make for a very interesting discussion, complementing other parts of the book.
The next few chapters provide a thorough discussion of photographic materials, atmospheric effects and photo processing. I enjoyed the text related to the dimensional stability, care and storing of films. There was detailed information regarding panchromatic (black and white), true color and false color (color infrared) films, and their applications in the industry. Detail was provided on the most popular films from Kodak (Eastman Kodak Company, Rochester, N.Y.) and Agfa Corporation (Ridgefield Park, N.J.) that are used in precision photography acquisition. The list was generally up to date at the time of printing. Since that time, however, new and improved products from both Kodak and Agfa have been announced such as Kodak's 2407 and Agfa's Pan 400 panchromatic films.
The discussion of the nature of the aerial scene and scene illuminance is quite informative. On the surface these topics may seem somewhat insignificant or overly simplistic in some ways, but they are important to the acquisition of quality photography. And the quality of the photography is extremely important as it sets the bar for the quality of all products that are produced after acquisition.
Information on atmospheric haze and its effects on imagery are timely. This discussion also includes detailed information regarding camera filters and their use in mitigating the atmos-pheric effects. Before the world of digital orthophotos, a good photogrammetrist could use marginal imagery to produce accurate planimetric and topographic maps. But the days of marginal photography are gone, as most clients require a digital orthophoto deliverable to supplement the traditional line mapping. Therefore, it is critically important to acquire high quality imagery with sharp contrast to gain an accurate visual representation of the landscape found in the imagery.
The information in the book on film processing is quite detailed and fairly technical in nature. Although the information provided is both accurate and informative, this discussion applies to a very limited audience.
Cameras, Accuracies and Aerial PlatformsNo text on aerial data acquisition would be complete without a thorough discussion of camera accuracy, aircraft platforms and mission planning. This text does an excellent job of presenting these topics in both an interesting and understandable fashion. It seems just right for the target audience and is ideal for the surveying or engineering professional who needs to understand what happens in the mapping shop once their project begins.
The authors discuss the calibration of mapping cameras to arrive at a precise focal length, the location of the fiducials (precision markings along the edge of the film that provide a rectangular coordinate system for image measurements), lens distortions and spatial resolutions. Accurate mapping can only be produced once these calibration values are precisely defined. One bit of information is incorrect, however, as the authors state on page 157, "mapping cameras usually require to be calibrated every year and before a mapping contract can be signed." In fact, most contracts in the United States do not require annual calibration of mapping cameras. Instead, it is common to have a requirement for a camera calibration current within three years. The calibration of a high-quality, precision photogrammetric camera will typically change very slightly over the three-year period and therefore the three-year calibration requirement has no detrimental effect on accuracy.
It should be noted that calibration is a costly and time-consuming adventure. The U.S. Geological Survey (USGS) Optical Science Laboratory in Reston, Va., provides the calibration for all U.S. cameras. The USGS highly recommends calling a year in advance to schedule the calibration. The more than $3,000 payment to USGS for the camera and almost $2,000 for each film magazine is only a small part of the overall cost of calibration. The camera must be removed from the aerial platform, carefully packed and shipped to Reston. Many firms choose to fly or drive the camera there in lieu of commercial shipping to protect their nearly half million-dollar investment. Finally, the opportunity cost of losing your camera for a week or two should not be overlooked.
Aircraft and InstallationsChapter 9 of the Manual covers aircraft platforms and includes a comprehensive graphic illustrating some of the popular aircraft used in imagery acquisition and their service ceilings. This is followed by detailed information regarding light single-engine, high performance single-engine, light twin-engine and pressurized turbo-prop aircraft. All of these platforms come with advantages and disadvantages when it comes to aerial acquisition, and the authors do a great job of detailing the differences between the various models of aircraft.
There was no mention, however, of the use of helicopters in imagery acquisition. Helicopters have been used for low-altitude, high-accuracy projects for several years. They also are being used more and more for LiDAR acquisition (the collection of elevation points from the air using a rotating laser). This area of the book could be improved by detailing the significant differences among helicopter acquisition and that of the more conventional approach using fixed wing aircraft.
Information is also provided on aircraft costing in this chapter. This should be required reading for all surveying and engineering professionals who work with mapping, as most people don't understand all the complexities that go along with owning and operating an aircraft for aerial acquisition. The four pages in the book dedicated to these cost factors are enlightening.
The most important topics in mission planning are explained at just the right level and the inclusion of several real-world numerical examples and quite a few illustrations help the reader to understand the text. The authors do a good job of describing the challenges associated with conducting aerial missions in mountainous terrain typically found in states like West Virginia and the differences compared to states with little terrain relief, like that found in Kansas.
New TechnologyThe book ends with discussions on two topics of major importance in the world of aerial survey: airborne laser terrain mapping (ALTM) and digital cameras. The use of airborne laser terrain mapping, or LiDAR, in the photogrammetry industry is growing exponentially. The rapid expansion in LiDAR hardware technology is fueling this growth. Therefore, it isn't all that surprising that the discussions of hardware in this portion of the book are somewhat dated. For example, the book discusses Optech's (Toronto, Ontario, Canada) recent addition in their ALTM inventory of the model 1210, which has an operating ceiling of 1,200 meters and a nominal collection frequency of 10 kHz (10,000 elevation points per second). Optech has announced several new models since the 1210 hit the market. In fact, the company announced its newest addition of the 100 kHz platform at the International LiDAR Mapping Forum held in Orlando in February 2004. Nevertheless, the technical discussion in the book is full of great information for anyone wanting to learn more about this exciting technology.
The discussion of digital imagery in the text is equally informative. The future of digital imagery acquisition is upon us. Unlike LiDAR technology, however, we are early on the technology curve with digital sensors, and therefore we will see many new developments in this arena in the next couple of years. At present, only a handful of U.S. aerial firms have purchased high-performance digital cameras. I was both surprised and pleased that the text includes detailed information on Leica's ADS 40 and Z/I's DMC sensors, both recent additions in the market. These two companies have taken very different approaches for meeting the technological demands for high-end digital cameras. The authors did a thorough job comparing and contrasting the two sensors.
Overall ImpressionWhy is this book important to the practicing surveying, engineering or GIS professional? With a general understanding of what takes place inside the mapping professional's office, you can become a more informed consumer. This can lead to two very important outcomes: saving money on the typical project through better project planning and ensuring that you get all the information and accuracy that you need in a map to fulfill your project needs.
I would have enjoyed a little more information regarding controlling aerial imagery. Moreover, the reader would have benefited from a detailed discussion of the importance of inertial measurement in aerial collection, as this is another exciting technological area enjoying exponential growth within the industry. Overall, the text is a great source of information relating to aerial acquisition and is a resource that I will gladly place on my bookshelf.
About the BookManual of Aerial Survey,
Primary Data Acquisition
By Roger Read, FRPS, FBIPP, Dip Ed Tech, FRSPSoc, and Ron Graham, PhD, CPhys, FinstP, AMRAeS
Whittles Publishing, Scotland, UK
Copyright Â© 2002
USA ISBN 0-8493-1600-6
Purchase this book online by clicking here.