662

UNITED STATES COAST AND GEODETIC SURYEY.

ï7o. 3, Report for 1893 of the Superintendent of the United States Coast and Geodetic Survey. Also, Dr. C. Koppe and Prof. P. Steiner give preference to the arithmetieal method for photo-grammetric surveys in general.

GENERAL ARITHMETIC DETERMINATION OE THE ELEMENTS OF THE ITALIAN PHOTOGRAPHIC PERSPECTIVES.

The panoramic views which subserved the map making were obtained by ten successive exposures. After each exposure the caméra was moved in azimuth by a horizontal angie of 36°,

and as each plate subtends a horizontal angle of 42°, the two ends of adjoining plates hâve a common mar-gin of a width of 3° in arc, corresponding to a width of 15 millimétrés. These common margins of two adjoining plates serve principally to ascertain whether the adjustments of the phototheodolite hâve g been changed during the occupancy of a station.

——(«) Orientation of the picture trace.—The horizontal projection of one complété panorama com-posed of ten plates will be a regular decagon, fig. 38, with a radius of the inscribed circle equal to the principal focal length (constant) of the caméra.

P', P2, .... P10--(horizontal) picture traces,

V = panorama station,

DP'=UP2 = . . . . DP10 =/ = principal focal

length of caméra.

After the position of one panoramic view has been platted on the map, its picture trace will be oriented, and with it the remaining nine views of the panorama.

After the horizontal angle go, fig. 39, included between the principal ray VP' of view P' and the horizontal direction to the triangulation point S, fig. 39, bas been platted

the orientation of each succeeding view P2, P3............P10 is accom-

plished by adding successively 36°, 72°, 108°.............(36°—go°) to

the angle go.

(b) Platting the Unes of direction topieturedpoints of the terrene.—The orientation of the panorama hav-ing been made, the lines of direction to points pho-tographed on the panorama plates may readily be platted.

The plate ilOT, fig. 39, may represent a vertical photographie plate oriented with refer -ence to the known point 8, pietured on MN as s.

s

O O1 = horizon line, O— —

V = point of view of the perspective v MN,

œ = angle of orientation for this plate with reference to 8,

VP=f= (principal) focal length, ss1, perpendicular to 00' =y = ordinate of the image s,

sxperpendicular to ff =x= abscissa of the point s.

• S

,û

-&■

Fig.39

From the rectangular triangle VP1 s', fig. 39, we find :

x = f tan go.

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