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An Innovative System for Low Cost Airborne Video Imaging
4. Software for Processing Airborne Video Imagery Airborne video imagery can be used in two ways: either as a source of spatial data where sequential images are mosaicked together to form continuous image strips, or where the original moving images are used. Either way, software must be developed for processing and value-adding in order to create a useful spatial data product. 4.1 Software for processing discrete frames In the past many different methodologies have been presented for processing sequential frames of video image data to create continuous image strips ([6], [5]). Some of these methods are more complicated than others, and some are more successful than others. A simple methodology is presented here for mosaicking images together. An image matching algorithm automatically extracts tie points from the overlap area between two sequential images. Using those tie points, the pair of images are registered to each other using a conformal transformation function. That transformation function is then used to estimate the alignment of the next image in the sequence. In this way the search space for tie points between the second and third images is greatly reduced, hence speeding up the process of automatic image matching. This process is repeated for all of the images in the sequence. It is important that a conformal transformation function is used in the mosaicking process since this reduces the degree which errors are propagated in the registration process. Higher order polynomial transformations functions propagate errors much more rapidly, even though they may initially give better registration results. Some typical image mosaics are shown in figure 5.  Fig. 5. Typical image mosaics from airborne video imagery 4.2 Software for utilising continuous image sequences (movies) In addition to using airborne video data for creating spatial image mosaics, the movie data can also be extremely useful for applications such as asset mapping (pipelines, powerlines roads etc.). However, to derive full benefit from the data, it needs to be processed to add value. One way of adding value to the data is by annotating the movie with information such as data and time of acquisition, and latitude and longitude of the camera. As a part of this investigation into airborne video imaging, software has been developed by the author for this purpose, the result of which is shown in figure 6.  Fig. 6. Annotated video imagery The images shown in figure 6 are three images that have been extracted from the processed movie file. All of the images in the movie file have been annotated with date of acquisition (1st June 2005 in this example), and latitude and longitude of the camera at the time of acquisition. Further information, such as type of camera used, time acquisition, flying height etc., can all be added as required. By spatially and temporally referencing the images in this way greatly increases their value to the end user, and makes them more accessible through a GIS. In summary, software for processing airborne video data is essential to ensure that the end user can derive full value for the imagery. There is little available commercial off the shelf software for processing airborne video data, hence the reason that the software described here has been custom developed. The next section of this paper now describes how the three components of the proposed system, camera, platform and software, are brought together to create an innovative, low cost aerial mapping system. 5. Mapping from powered parachutes 5.1 Overview of video mapping from powered parachutes So far this paper has described the three components essential for any aerial mapping system (the camera, the platform and the software) with an emphasis on low cost and flexible data acquisition. By combining a video imaging system with a powered parachute and custom developed software results in an aerial data acquisition system that is easy to build, cheap to fly, and can be used in some the of the most remote parts of the world. The specific advantages and disadvantages of airborne video acquisition from powered parachutes are listed in table 1. Table 1. Advantages and disadvantages of mapping from a powered parachute
Although the proposed system does have some limitations, they are not all considered to be important. For example, the limitation of not being able to use the system for wide area mapping is somewhat irrelevant since that is not an application for which the system is designed. Additionally, the spectral and geometric limitations of video data well known, so video data should only be used as a data source when these limitations do not impact negatively on the application. The other disadvantages of this system (weather and software availability) cannot be avoided, however, and must be worked around. 5.2 Typical applications The typical applications for which the proposed imaging system can be used are dictated by the attributes of the system. The spectral and geometric limitations of the video imagery makes it unsuitable for advanced remote sensing applications, such as vegetation health studies or topographic mapping. However it is useful for:
In addition to the applications listed above, there are no doubt many other scenarios where the system can be usefully applied. 5.3 Implications for developing countries An important potential use for the proposed imaging system in is developing countries. Previous studies have suggested that developing countries have a need for low cost, simple to operate systems that can be put in place very rapidly [10]. If this is the case, which it no doubt is in some developing countries, then the proposed system would be potentially very beneficial. Powered parachutes are ideal platforms for use in developing countries due to the simplicity of their construction and low maintenance requirements. They are typically powered by 58 horse power, 2 stroke engines, which can be maintained and serviced by any moderately qualified engineer. The challenge is now to prove the value of airborne video data acquired from powered parachutes, through some form of validation programme, to encourage organisations to take up this new technology. 6. Concluding remarks This paper has discussed the merits of acquiring airborne video imagery from a powered parachute. The system is cheap, flexible and simple to implement and operate. It can be used for a variety of mapping tasks, and is particularly applicable to use in developing countries, where spatial data is required, but where sources of data are very limited. Although it suffers from some drawbacks, they are not significant, and do not negate it’s potential effectiveness. The first stages of development of this system have already been carried out. The platform has been tested for stability as an aerial mapping platform, and from the data collected it has been shown to be very suited to this type of work. The next stage of development of the proposed system is to source funding from interested organisations who wish to support the validation phase of this project. Once validated there is nothing to stop the system being transferred to anyone who has a need for it. 7. References
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