Aerial Perspective: Softcopy Photogrammetry

Advances in digital aerial photography and LiDAR mapping techniques have recently captured most of the aerial mapping headlines. Meanwhile, a quiet revolution is taking place: Softcopy photogrammetric techniques are radically advancing mapping productivity.

What is Softcopy Photogrammetry?

Also known as digital photogrammetry, softcopy uses manual and automatic techniques for capturing, processing, and analyzing digital imagery—beginning either by scanning analog film or by direct digital image capture. The core concepts and mathematical functions remain the same as in traditional photogrammetric techniques developed over the past 100 years; the main difference is that softcopy uses digital imagery. The capability of handling image data of various sources with different geometric properties in a single workstation makes the system powerfully versatile and productive.

Historical Perspective

Analog photogrammetry was the first stage of development for functional mapping systems. It employed optical-mechanical components and analog stereo photographic film images recorded on film or glass diapositives. The solution was achieved by means of physically altering the positions and rotations of the stages holding the film media relative to each other. Early systems produced only hardcopy maps while the advent of computers made possible modified systems capable of limited digital data recording.

Analytical photogrammetry represented the second developmental stage. Similar hardware and film components were employed, but the solution was achieved by mathematical methods using a computer to calculate solutions and record the compiled data.

In the current softcopy system, analog film has been replaced by digital imagery. The costly optical-mechanical components have been completely replaced by computers and monitors. The solution is obtained mathematically using basic photogrammetric concepts and image-processing techniques.

Softcopy Evolution

With the advent of increasingly affordable scanners, computers, and high-capacity storage, softcopy system development started in the late 1970s and was introduced to the photogrammetric community in the late 1980s. Early systems lacked high image quality and speed, but these problems were easily overcome by later computer innovations. At present, the transition from analytical to softcopy is nearly complete. Results from numerous research and development efforts by a host of vendors have led to significant efficiencies through increasing automation of aerial triangulation, stereo model orientation, and DTM extraction. With the availability of digital cameras and satellite imagery the transition to softcopy systems has been inevitable.

Softcopy Advantages

Clearly softcopy techniques and systems have quietly but surely become the mainstream photogrammetric system of choice due to their inherently greater flexibility and efficiency. The advantages are numerous.

Economics: The cost of a complete softcopy system is a fraction of an analytical system. Software modules can be added as needed. Nearly all photo lab operations are eliminated and, when paired with a digital camera, scanning is also eliminated. Considerable additional cost reduction can be achieved due to automated processes in AT and elevation data extraction as well as in overall data collection time.

Image Quality: Various sources of digital images widen the user's scope to collect and interpret the required data more efficiently and accurately. Eliminated are data integrity and stability concerns caused by shrinkage and other degradations. Dynamic radiometric corrections allow the user to change the image characteristics to show details otherwise hidden in the image. In the case of direct digital camera recording, data is stored at a bandwidth of up to 16 bits/ pixel without grain noise. This allows for better matching accuracy and success in automated processes.

Quick Response to Evolving Situations: Using today's technology in airborne GPS control and inertial measurement data, AT time can be reduced or eliminated, and mapping can often be delivered to clients in days instead of months.

Simplified Workflow: Once the model orientations are established by automatic means, stereo-imagery can be displayed instantly on the screen. This enables compilers to spend more time collecting data and less time solving orientation problems.

Versatility: The same softcopy system can be employed for different tasks and products. Add-on software modules can be easily integrated without the need for additional hardware components.

Future Trends

Advances in airborne GPS and inertial systems will further reduce the need for aerial triangulation and ground control. All intermediate processes including fi lm processing, scanning, and photo lab operations will be completely eliminated as the digital camera is adopted by more mainstream mapping organizations. The time required for compilation and processing of photogrammetric mapping data will be further reduced by the final transition from analog and analytical approaches to a complete softcopy workflow. Already in process elements such as automatic AT, automatic elevation data extraction, and orthophoto generation, time has been reduced to a small fraction of that required by previous methods. Further developments are underway on all these fronts.

The locus of skills needed in softcopy photogrammetry will continue to shift from the nuts-and-bolts dexterity required for operating analytical stereoplotters to the macro-writing, computer networking, and web-based operations skills complementary to the computer-based workflow. In a fully digital environment, these skills have become critical to the success of mapping organizations.

Without great fanfare softcopy techniques and systems have quietly matured to become the photogrammetric system of choice. However, the full potential of softcopy is yet to come. The quiet softcopy revolution will continue to dramatically enhance the abilities of aerial mappers to respond rapidly and efficiently to an increasing variety of client-driven geospatial needs.

About the Author

George Maalouli is vice president and chief technical officer of the Seattle Division of Aero-Metric, Inc. He holds a M.Sc. in aerial surveying from the International Institute for Aerospace Survey and Earth Sciences (ITC) in the Netherlands and has been actively involved in photogrammetry for 16 years.

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