July 20, 1896.

THE AUSTRALIAN PHOTOGRAPHIC JOURNAL.

165

PHOTOTOPOGRAPHY.

Paper by Pietro Baricchi,

Government Astronomer, Victoria.

Member of the Amateur Photographic Society of Victoria.

Phototopography is not a new art. It was thought of even in the days when Daguerre’s discoveries had just been made known.

Its purpose, briefly stated, consists in obtaining from photographic views the necessary data for the construction of a complete and accurate topographic map of a given region, showing all the detail both in plan and elevation which it is possible to plot, compatibly with the scale adopted in accordance with the requirements of the case. The pictures, when certain adjustments of the camera are carefully attended to, being formed on a vertical plane which intersects all the rectilinear rays emanating from every point in the landscape, are true perspectives; the main object, therefore, is to evolve from a set of such perspective views, taken from judiciously selected stations within the area to be mapped, a geometrical projection, on a horizontal plane, of the region concerned; and the principles by which this object is attained are those taught by Descriptive Geometry.

This method of mapping was known long before the invention of Photography, and we are told (appendix No. 3 report of the Superintendent of the U.S. Coast and Geodetic Survey, by J. A. Flemer), that the celebrated Hydrographer Beautemps-Beaupre succeeded in constructing Topographic maps of a part of Van Diemen’s Land and other places from perspective sketches of coast regions made during a scientific expedition in 1791-03. The method, however, owing most likely to the great skill required in making accurate drawings, could not be expected to take a conspicuous place in topographic surveying, and it does not appear to have been employed by others to any great extent until, some 60 years later, the camera, in the hands of Colonel Landessat, of the French Army, took the place of the sketcher, and Phototopography then seriously commenced its career.

The experimental stage did not last long, for in 1861 this officer executed an accurate map of a part of Paris by the aid of photographic views, and in 1864 published in the “ Memorial de l’Officier du Genie ” a complete exposition of the methods employed in Photo-Surveying, which Lieut. Henry A. Reed, in his work on “ Photography applied to Surveying,” describes as “so exhaustive that at the present date no treatise upon this subject can be complete without making use of the results of his (Landessat’s) researches, and no practice perfect without applying the principles that he established.” By this time the new art had commenced to draw the attention of prominent men outside of France, and its progress thenceforth was rapid.

A considerable amount of literature dealing with the subject accumulated year by year in almost every language, thus largely increasing the number of workers, and soon the introduction of dry plates, instrumental improvements, and experience acquired in actual practice smoothed down the difficulties of photo.-surveying, facilitated its operations, and conquered one by one all objections raised against its capabilities.

Phototopographic surveys of vast and difficult regions were undertaken and accomplished with astonishing results, and if any doubts still remained as to the adaptability of the methods in question, the unreasonableness of such doubts could be clearly made manifest by the achievements of Italy and Canada in this class of work.

Besides France and the two last-mentioned countries Austria, Germany, Belgium, America, and other nations have fully recognised the merits of Phototopography, and its employment is rapidly becoming general. This Art or Science, or combination of both, offers a most advantageous application in mountainous districts, in reconnaissance surveys for the study of new routes, roads or railroads, in hydrographic and military operations, settlement schemes, exploration, geological surveys, river ameliorations, mining and irrigation projects, and any other purposes where an accurate and complete representation of a given locality is a first requisite.

It is well known that the making of extended topographic charts in Europe by the ordinary methods has invariably necessitated an amount of labour, time, and expense as to render similar undertakings almost beyond the strength of younger countries as Australia and even America; and that, in fact, notwithstanding the recognised desirability for such topographic maps, none yet exist here—at least none approaching to any degree of completion. But, with the camera as an adjunct, the conditions are greatly changed, for it has justly been said that by its aid, and with regard to topography, the patient and arduous toil of a generation may be accomplished in a few years.

It is not intended to give here an exposition of the theories, nor a full account of the instrumental means and methods employed either in the field or in office work, for the execution of phototopographic surveys. Such an undertaking would be superfluous, in view of the complete treatises on the subject published by Landessat in France, Cap. E. Deville in Canada, Paganini in Italy, Lieut. Reed in America, besides other contributions to Societies’ transactions, periodicals, &c.; but it seems opportune, especially in order to bear out what has been said above, to mention briefly some points in connection with what has been done lately in Italy and Canada, the two countries which at present are probably the most conspicuous exponents of activity in the application of photography to surveying. In Italy this work has been carried out since 1878 by the Royal Geographical Military Institute, at the instigation of General Ferrero. The successful completion of Topographic maps to a scale °f with hypsometric contour lines at every ten metres, constructed from photo, surveys of broken and difficult

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