The Stereoscopic Method of Surveying and a First Trial of Its Application to a Railway Survey in China

In order to demonstrate the advantages of the stereo-photographic method of surveying, the writer made a survey, for a part of the proposed Hankow-Ichang Railway, through a difficult piece of country in the very rough and tortuous valley of the Yangtze Kiang River, in China. The instruments and methods used are described and illustrated in detail by their application to this survey. The photo-theodolite is a combination of a metallic box camera and a theodolite; the optical bases are measured with a rod, mounted on a tripod; the three co-ordinates of each point on the negatives ( or diapositives) are measured on the stereo-comparator, which, perhaps, is as important an instrument as the photo-theodolite in stereophotographic work; the points are plotted on a special drawing device consisting of a glass plate to which steel rulers a.re pivoted and clamped. The other apparatus consists of double plate-holders, photographic plates, etc., etc.