Topographical Surveying: Including Geographic, Exploratory, and Military Mapping, with Hints on Camping, Emergency Surgery, and Photography |
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Common terms and phrases
accuracy accurate adjustment alidade altitude aneroid angulation astronomic axis azimuth backsight barometer base bench-marks camera Chap clamped Coast and Geodetic collimation column computed contour interval contour lines correction cross-hairs determined diff difference direction distance elevation employed equation error executed feet Geodetic Astronomy Geodetic Survey geographic hachures height horizontal inches instrument intersection latitude length levelman logarithms longitude means measured ment meridian meters method micrometer miles mountain object observed obtained odometer parallel plane plane-table plate platted points Polaris position primary traverse primary triangulation projection range-finder reduced refraction right ascension rodman scale screw sheet side sight signal sketching slopes spirit-leveling square square miles stadia star station stream surface TABLE tangent tape telescope theodolite tion topographic map topographic survey transit trigonometric tripod U. S. Coast U. S. Geological Survey vernier vertical angles zenith zenith telescope ΙΟ
Popular passages
Page 573 - Upon the telescope is a mirror and two rings, the axis of the rings as well as the center of support of the mirror being parallel to the line of sight of the telescope. The telescope being directed upon the observing station, the mirror is so turned as to reflect the sunlight through the rings and necessarily to the observing station. In many cases...
Page 583 - Other things being equal, therefore, the measures of such special angles should show less range than the measures of other angles. Besides the instrumental errors of the periodic class, there are also accidental errors of graduation. These .ire in general small, however, in the best modern circles, and their effect is sufficiently eliminated by shifting the circle in the manner explained above for periodic errors.
Page 756 - ... the error in the setting of the instrument in the meridian. Its effect is zero at the zenith and increases toward the horizon. Since the instrument is liable to be disturbed during the operation of reversal, it is necessary to determine the azimuth error, both before and after reversal, separately. A comparison of the clock error, determined from observations upon north and south stars, will furnish the data necessary for the determination of azimuth. Practically, it is determined by elimination...
Page 458 - In the space between any two contours are found elevations above the lower and below the higher contour. Thus the contour at 150 feet falls just below the edge of the terrace, while that at 200 feet lies above the terrace; therefore all points on the terrace are shown to be more than 150 but less than 200 feet above sea. The summit of the higher hill is stated to be 670 feet above sea; accordingly the contour at 650 feet surrounds it.
Page 588 - B to C, etc., are by this method observed separately; and whenever there is sufficient time at the observer's disposal this method should be followed. Besides measuring single angles, it is desirable to measure independently combined angles — ie, angles which consist of the sum of two or more single angles. Thus, supposing...
Page 196 - The angles which the lines ab and a'b' make with each other is the error in position. By constructing now through ca line cd', making the same angle with cd as that which ab makes with a'b', and directing this line cd' to D, the table will be brought into position, and the true point c can be found by the intersections of aA and bB. Instead of transferring the angle of error by construction, we may conveniently proceed as follows, observing that the angle which the line a'b' makes with ab is the...
Page 684 - An apparent solar day is the interval between two successive transits of the sun across the meridian. The apparent solar...
Page 458 - In the map each of these features is indicated, directly beneath its position in the sketch, by contours. The following explanation may make clearer the manner in which contours delineate elevation, form, and grade: 1.
Page 590 - ... sets of measures will be required, all measures being made according to the programmes given above. Under ordinary circumstances and with due care in centering, angles measured as specified above should show an average error of closure of...
Page 345 - ... tested by means of an official standard, and the error, however small, recorded and applied to each rod reading. Changes in rod length due to variation in temperature and moisture are so small that they may be disregarded in rods made of the best quality of well-seasoned white pine treated with paraffine as described in Article 145. 149. Divergence of Duplicate Level Lines. — A curious fact, probably first noted in the United States in the report of the Chief of Engineers of the Army for 1884,...