Tracing Evolution
Little did the French geodesist Arago know of its far-reaching implications, when in 1840 he first recommended the use of photographs for the preparation of topographical maps. His approach did trace the years to become a major breakthrough a decade later, as a widely used tool in the field of mapping. The true elaboration of this technique however, took place in the hands of another Frenchman named Colonel A Laussedat. He founded the scientific technique in greater detail developing the required specifications. He called this technique 'Metrophotographie' which involves mapping work from 'terrestrial photography' taken by a phototheodolite. In 1858, Nadar used a balloon at 80-meters to obtain the first aerial photograph. A year later, Laussedat came out with a descriptive methodology of surveying from photo-theodolite. In 1867, he also exhibited a plan of Paris prepared by photographic surveys.
The oldest surviving aerial photograph is of Boston, USA, taken by james Wallace Black in 1860
At this similar time, a number of noteworthy researches sprung up from the same region. Dr A Meydenbauer independently carried out measurements of architectural details using two photographs of a building. Simultaneously, in Germany in 1873, photographs were used by Jordan for the survey of Datchel Oasis and by S Finsterwalder for the survey of Alpine glaciers. Soon, Hauk developed the important 'epipolar theory' in 1883 and constructed the 'perspectograph', an apparatus for construction of third perspective from two given perspectives. After many major breakthroughs like these, importance of balloon photography came into picture. This actually proved and defined the importance of aerial photography. Stereo-photogrammetry soon came into use with the discovery of the principle of the floating mark in 1892. In the twentieth century, with the development of aeroplanes, aerial photogrammetry in the present sense was practically started.
The Indian Initiation
The use of photogrammetry started in India slightly later than the global trend. Survey of India initiated it towards early 20th century. It was started with Terrestrial photogrammetry when a phototheodolite of Bridges -Lee make was procured in 1899 for the evaluation of its mapping potentialities. With the start of First World War (1914-1918), air survey and the technique of preparation of topographical maps from air photographs started to meet the needs of war. This also led to a wider implementation and recognition of this technique. In view of developing the air photo mapping of the First World War, Captain H H Thomas of the Royal Air Force was deputed to visit India in 1918-19, for advising the Indian Government in the peace-time-uses of air survey.
In 1928, Survey of India department purchased one WILD Phototheodolite. During 1928-29, Lieutenant I H R Wilson attempted cadastral survey on the scale of 66 inches to 1 mile in the Almora district of Uttar Pradesh from terrestrial photographs taken by the WILD Phototheodolite. But this type of photogrammetry was not found suitable for Indian terrain except in very high hills. In 1939-40 some military air survey exercises were carried out in Naushera with the primary object of rapid production of 1:50,000 scale topographical maps and 1:25,000 scale battle maps. During these years air survey was carried out mostly for more detail, with the contours either being surveyed on the ground or by using oblique photographs. Until Second World War, Survey of India was only confined to the preparation of special maps for the Northern Command and the Air Force. After World War II, air photographs were widely used to produce standard topographical maps as well as project maps on all scales for development schemes and sectors like irrigation and hydroelectricity. This increased the scope of usage of this technique for a wide segment of the society. In 1948 Brigadier G F Heaney, Surveyor General, initiated the proposal for training of the Survey of India officers in London, with a view to introduce photogrammetric survey in India. During the period 1954-66, sufficient experience was gained in India in the photogrammetric survey methods employing precision plotters. With only one WILD A7 and WILD RC 5a aerial camera in 1954, they developed rapidly in this sphere, adding a number of precision plotters.
The Entrance of Digital Photogrammetry
In 1958, Helava invented the Analytical Plotter, which improves the performance in photogrammetry with respect to better economy, higher degree of accuracy and increased speed. The first detailed concept of a fully digital stereoplotter with a central processing unit emerged in the year 1981. This had the same functionality as analytical stereoplotters, but with some major differences. Let us briefly dwell upon these basic differences. The digital photogrammetric workstations are different from the old plotters by three aspects: the data and sensors used, the hardware and user interface and the software and automation tools. In 1988, the first fully digital photogrammetric instrument was available. It enhances the photogrammetric works, aerial triangulation, feature and elevation collection and orthophoto production. One of the most obvious requirements for digital photogrammetry is digital image, which is either accomplished by scanning film transparencies of aerial photographs or by using digital images.
Now-a-day's aerial photography has been into a new trend called Digital photography, which is capable of delivering photogrammetric accuracy and coverage as well as multispectral data. A digital camera used as one of the instruments for acquiring the input data for digital photogrammetry, not only reduces the need to scan photographic negatives but also eradicates the systematic error sources due to film unevenness and distortion. The imagery can also be downloaded and processed within minutes of acquisition. It is advantageous as no chemical film processing or scanning, is to be done.
With the development in the field of Satellite Remote Sensing, satellite images are also used as the input data for Digital Photogrammetry. Hence, we can say that there is a clear movement towards 'Imagegrammetry' from Photogrammetry. In stereo-photogrammetry, the bundles of rays are reconstructed but when we talk about digital photogrammetry using satellite data we don't have to bother about this reconstruction, as height is too much to have any height distortions due to relief displacement. Also we cannot prepare DEM in photogrammetry using only satellite images although it's good for preparation of small-scale topographic maps.
Summing up
Photogrammetry is a more cost effective method of mapping a large area than surveying on the ground. However, there are not a lot of photogrammetry companies around due to the extremely high cost of equipments and number of skilled operators required. Although India has developed a lot towards Remote Sensing, aerial surveying and mapping but in the field of photogrammetry there is still to look ahead to. Indian photogrammetric market has very few players like Survey of India, National Remote Sensing Agency (NRSA), RRSSC, PAN India, Speck Systems, Genesys, Rolta, RMSI, DSM soft and various departments of Department of Space (DOS) and also some overseas companies like Kampsax India, Leica, DVP, PCI Geomatics, etc.
Even now the largest requirement of the photogrammetric techniques in the Indian Government sector is with Survey of India as they are involved in preparation and updating of toposheets, tour guide maps and other large-scale projects using German make WILD analog stereoplotters. However at present, the organization is moving towards digital photogrammetry. Certain activities in this direction are evident. Camera calibration record i.e., inner orientation elements, is essentially required for the digital photogrammetry but not available in old aerial photographs taken by Air Force.
National Remote Sensing Agency (NRSA), a leading government organization involved in Aerial Photography, Photogrammetry and Digital Mapping is involved in preparation of Analogue/Digital GIS compatible map. They are using Analytical and Digital Photogrammetric system for the preparation of topographic maps. Interestingly, one finds that users in the field of photogrammetry having analog, analytical and digital devices are still inclined towards analytical plotters. Analytical plotters giving more accuracy (compared to digital) in less time and effort (compared to analog) are generally seen as the reasons. Compared to analog stereo-plotter, analytical stereo-plotters have advanced inner, relative and absolute orientation functions. Also no extra training has to be given to the operators for analytical devices as same skill can be utilized with increased speed and accuracy. The developments in photogrammetry, from around 1850, have followed four main development cycles [Konecny, 1985]. Each of these periods extended about fifty years :-about 1850 to 1900 - Plane Table Photogrammetry; about 1900 to 1960 - Analog Photogrammetry; about 1960 onwards -Analytical Photogrammetry; and from about 1981 onwards - Digital photogrammetry. It is apparent that the photogrammetry market is moving towards Digital Photogrammetry because of its portability, speed and accuracy. However, due to the vital drawback of induction of error at the time of the scanning of photographs, analytical photogrammetry still seems to enjoy confidence over digital. Again, on the pros side, digital images used instead of scanned photographs, lead to an output of the best of kind. Digital Photogrammetry enables us to quickly and efficiently capture 3D vector data from aerial and satellite imagery and create orthophotos and topographical maps. Based on the need of degree of accuracy the user can choose between the use of Analytical and Digital Stereoplotters. Digital Stereoplotters are around 3-4 times cheaper than Analytical Stereoplotters, extending to the reach of small companies and educational institutions. Due to the use of digital images, processing and transmission of data will be fast, leading to quantum jump in the business. So now time has come to gain strength in Digital Photogrammetry and if small companies join together, any nation can respond to any demand of the world. It is truly an exciting and interesting new avenue that is seemingly emerging with a wide road of challenges ahead.
