Bulletin of the United States Geological SurveyThe Survey., 1906 - Geology |
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Common terms and phrases
accuracy alidade aneroid ASTRONOMIC DETERMINATION ASTRONOMIC TRANSIT axis azimuth base line chief of party chronograph chronometer circle clamp Coast and Geodetic computed consists declination degree detail DETERMINATION OF POSITION difference economical elevation eliminated elongation equal equation error exprest feet Geodetic Survey height heliotroper HENRY GANNETT HORIZONTAL ANGLES hour angle inches instrument latitude length located by intersection longitude means ment meridian method Microm micrometer miles minutes necessary Newt object OBSERVATIONS FOR AZIMUTH obtained plane table plane-table sheet platted points Polaris possible PRIMARY CONTROL primary traverse primary triangulation proper motion read microscope record right ascension scale secondary triangulation selected sidereal sight line signals sketching Spearville Spherical angle spherical excess stadia star tape Telescope south temperature theodolite thread thru tion topographic transit traverse lines tripod U. S. GEOLOGICAL SURVEY United States Geological vertical Walton wires zenith telescope
Popular passages
Page 49 - On deck protected" the cylinders shall be protected from the direct rays of the sun by means of structural erections or awnings. Tarpaulins covering cylinders and in contact therewith are not considered adequate protection. Protection by use of wood dunnage Is permitted. [CQFR 53-54, 18 FR 8239. Dec. 16, 1953] § 146.24-35 "Under deck" stowage. (a) Cylinders stowed "Under deck...
Page 32 - ... station, both before and after the campaign, and observe for time each with his own instrument, or with one similar in all respects to that used in the campaign. A comparison of the time determinations made by the two observers gives an approximation to the personal equation. A better method, but one not always practicable, is for the observers, having completed half of the observations for time and longitude, to exchange stations for the remainder of the work. The mean of the results before...
Page 11 - They are made also for the purpose of checking and correcting positions determined by primary triangulation and primary traverse. With regard to the checking of primary triangulation by astronomic determinations, it should be understood that in the case of a single determination the work by triangulation is far more accurate than that by the astronomic method, even when made under the best circumstances. It is, therefore, desirable to introduce checks of this kind upon primary triangulation only...
Page 60 - Each triangle, therefore, furnishes an equation of condition, which is known as an angle equation. The number of angle equations in any figure is equal to the number of closed triangles into which it can be resolved. But since certain of these are a consequence of the others, the number of angle conditions which it is desirable to introduce is less than the number of triangles. The number of angle equations in any figure is equal to the number of closed lines in the figure plus one, minus the number...
Page 52 - If for any reason it should be necessary to wait longer, it will be best to make a new reading on the first signal. The precision of centering an instrument or signal over the reference or geodetic point increases in importance inversely as the length of the triangulation lines. Thus, if it is desired to exclude errors from this source as small as a second, one must know the position of the instrument within one-third of an inch for lines a mile long or within 6 inches for lines 20 miles long. The...
Page 64 - E, in which dL is the difference in latitude. K, the. distance between the stations in meters. a', the fore azimuth of the line connecting them, measured round clock-wise from the south through the west. h, the first term.
Page 27 - ... determination of azimuth. Practically, it is determined by elimination from equations involving the mean of all these stars observed in each of the two positions of the instrument, after correcting for level, and as it is slightly complicated with collimation it must be reached by two or more approximations. The error is essentially positive when the telescope points east of south, and negative when west of south. The correction applicable to any star is exprest in the equation, cor.
Page 52 - ... remembered relations will serve as a guide to the required precision in any case : 1 second is equivalent to 0.3 inch at the distance of 1 mile. 1 second is equivalent to 3.0 inches at the distance of 10 miles. 1 second is equivalent to 6.0 inches at the distance of 20 miles. 1 minute is equivalent to 1.5 feet at the distance of 1 mile. The notes should always state explicitly where the instrument and signals are and give their co-ordinates (preferably polar co-ordinates) if they are not centered....
Page 60 - The number of angle equations in any figure is equal to the number of closed lines in the figure plus one, minus the number of stations. Thus, in a closed quadrilateral, the number of angle equations is 6 + 1 - 4 = 3. There is another class of conditions, known as side equations, which can be best explained by reference to a figure. In the diagram, suppose the figure 0, 1, 2, 3 to represent the projection of a pyramid, of which 1, 2, 3 is the base and 0 the apex. A geometric condition of such figure...
Page 60 - The measured angles of each triangle should equal 180° plus the spherical excess. Each triangle, therefore, furnishes an equation of condition, which is known as an angle equation. The number of angle equations in any figure is equal to the number of closed triangles into which it can be resolved. But since certain of these are a consequence of the others, the number of angle conditions which it is desirable to introduce is less than the number of triangles. The...