. Railway maintenance engineering, with notes on construction . ontal plate with a circle is frequently pro-vided upon which the angle can be read as with a transit and theviews oriented from these readings in the subsequent plotting in theoffice. In very rough country, as in the Canadian surveys, a smalltelescope may be mounted on the camera for reading the verticalangle, but in ordinary railroad work the camera is generally leveledand if the country is very broken a sufficient number of camerastations are located to enable the necessary detail to be 3 shows a photograph of the
. Railway maintenance engineering, with notes on construction . ontal plate with a circle is frequently pro-vided upon which the angle can be read as with a transit and theviews oriented from these readings in the subsequent plotting in theoffice. In very rough country, as in the Canadian surveys, a smalltelescope may be mounted on the camera for reading the verticalangle, but in ordinary railroad work the camera is generally leveledand if the country is very broken a sufficient number of camerastations are located to enable the necessary detail to be 3 shows a photograph of the Canadian survey used inmap construction*. The number of views taken at each stationdepends upon the angle of the lens. This angle varies in differentcameras, but the range is not more than from 30 to 45 taking the views they should overlap each other, and if theangle of the lenses is 45 degrees, the views should be taken aboutevery 30 degrees. * Topographic Surveying, H. M. Wilson, 1901, John Wiley & Sons,New York, p. 293. 6 RAILWAY MAINTENANCE. Pla^e. Fig. 3.—Photograph of Canadian Survey and Used in Map Construction. (Wilson.) Fig. 4 illustrates the method of plotting the results of the sur-vey. The triangulation A5 is first laid out to the scale of themap. Circles are then drawn with the camera stations .4 and Bas centers and with a radius equal to the principal focal length of the camera. The focal length canbe determined to within y-J-^ in. andthe circles are drawn with this lengthtaken actual size as the radius. To determine the horizontal loca^tion of any point as C the distanceCxCn is laid off on the trace of theplate from the center and the radialline Ac\ is drawn, another radial lineis drawn in a similar manner fromstation B^ and the intersection ofthese lines determines the location ofthe point on the 4.—Projection of Camera The vertical distance above or Plates from a Station. below the camera is calculated by
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1915
