Development and History of Mechanical Methods for Generating Maps of Smaller Scales (Especially for GATE-Geospatial 2022)

Glide to success with Doorsteptutor material for CTET/Paper-2 : get questions, notes, tests, video lectures and more- for all subjects of CTET/Paper-2.

Examrace Books on Mapping, GIS, and Remote Sensing prepares you throughly for a wide range of practical applications.

Elaborate plotting machines of the Fourcade, Zeiss and Wild types work to a luxurious standard for medium scales. It, therefore, becomes desirable to simplify the plotting and reduce ground control, consistent with the required standard of accuracy in planimetry and contours.

How to Construct and Interpret a Scale Map - Video & Lesson …

Old Methods

In 1915, Gasser proposed a system for projecting a pair of stereoscopic air photographs apparently partly based upon a method suggested earlier by Scheimpflug. A recent adaptation has led to the Zeiss Multiplex Aeroprojector, in which photographs are projected alternately in red and blue and then observed through spectacles with eye-pieces of complementary colours. This gives a plastic effect to the landscape, and by using a plotting table of variable height and carrying a floating mark, the plan and contours may be plotted. This is, in the application, the principle of the anaglyph, and the method is being given much attention at the present time. The introduction of this plotter is an important step forward. It is being extensively used in the U. S. A. and elsewhere. Wild have also recently produced a plotter (Autograph A6) of about the same standard. Both these instruments are now being used in conjunction with the larger ones. Recently, the Canadian Radial Stereo-plotter has provided a means of eliminating some of the graphical work in the Arundel Method.

Limitations of Old Methods

The great difficulty in all simple methods is the production of reasonably accurate levels with a minimum of ground control. This is particularly important from a military point of view Winterbotham remarked in 1929, that in the easy country a height control of four points per overlap would cost almost as much as a complete one-inch map. He emphasized the importance of the strip method and remarks that ″ the Fourcade instrument seeks to free the surveyor from many ground control requirements. The larger instruments are being increasingly used for horizontal and vertical control of large surveys, with minimum ground control, the detail and contours being plotted with cheaper instruments or by simple methods.

Modern Methods of Small-Scale Surveys by Oblique Photography or by Multi-Lens Photographs

The possibility of oblique photography interested those who wished to produce small-scale maps rapidly with a minimum of groundwork.

Gordon proposed a method of plotting from an oblique photograph. This method assumed that the point where the optical axis meets the plate and the tilt of the photograph are accurately known. This, however, is not the case and the difficulty of such determination has resulted in the method not being adopted.

It is chiefly in Canada that the oblique method has been developed and utilized, although experiments on a “navigational control” method of combined oblique and vertical photography were carried out in England by Jones and Griffiths prior to 1925.

The Canadian method is to fly a strip along which obliques are taken to the front and to the sides. Later a perspective grid suitable to the photograph is placed over it and plotting effected on the plan by proportion on to the squares of known size. Narraway states that given a suitable control of high accuracy a detailed topographical map can be plotted, on sales of the order of one inch to the mile, to an accuracy greater than the likely plotting error. He remarks that in one hundred and twenty-five thousand miles of Canada surveyed (1929) any point should be within 1/20 inch of its true geographical position. “This.” he concludes, “is better than could be expected of a similar ground survey.” It may be mentioned again that this method is only applicable to areas of slight relief.

More recent experience is given by Burns and by Burns and Field who describe a simple plotter for high oblique photographs. “It was obvious that the machines and methods first developed in Continental countries had no economic application in the construction of small- and medium-scale maps.”

Limitations of Modern Methods and Further Developments

Difficulties of obtaining accurate wide-angle camera lenses, and the inherent advantages of the vertical photograph for plotting purposes, led to the development of the multi-lens camera. This has taken several forms, but consists generally of a group of lenses in a fixed relationship, so that one vertical and a number of obliques are taken at each exposure. If the obliques are rectified, the final effect will be as taken by a single lens of a very wide angle.

The tri-lens camera in the United States, the nine-lens camera of Zeiss and the seven-lens camera of Barr and Stroud, has opened this field. The multi-lens seems to have possibilities for small scales, although recent improvements in wide-angle lenses have made single-lens photography available for much smaller scales.

Developed by: