bottom to top. Opposite the letter denoting a corner is given the bearing of the course running from that corner to the following one, in the order in which the survey was For instance, the bearing N 43° 20' E horizontally opposite A denotes the bearing of the course AB. The number opposite a corner in the column of distances is the distance of this corner from the preceding one. COMPASS NOTES-FORM NO. 1 The right-hand page is used for remarks and sketches. When no objects are to be located along the line, as in the case from A to B, no sketch is necessary. Between B and C, B N71°45′E C 287.8 ft. a sketch is drawn showing the location of a road and mill with respect to the line BC. The line being run is usually represented by the center line on the right-hand page, unless objects are to be located at great distances on one side of the former line, in which case 8 80 00 E it is represented by a vertical line drawn near the right or the left edge of the page, as may be necessary. This is illustrated by the lines PQ and KL, which represent parts of BC and DE, respectively. A number written in the column of distances be 347.4 ft. N31 15 W FIG. 22 M tween two letters denoting corners, indicates the distance at which the point horizontally opposite it in the sketch is from the immediately preceding station or corner. Thus, the number 100, horizontally opposite P, indicates that the distance from B to P is 100 feet. 39. Form No. 2 shows a method of keeping compass notes that is very clear and explicit, and is especially suited to surveys in which it is not necessary to locate any points or objects outside the main line. The notes here given are for the four-sided field represented in Fig. 22. The bearing and distance horizontally opposite any of the courses in the first column are, respectively, the bearing and length of that course. Thus, the bearing and length of CD are, respectively, S 80° 00' E and 287.8 feet. The lines are supposed to be run in the directions indicated by the letters: CD is run from C to D, not from D to C. 40. In simple cases similar to the one just illustrated, the best way to keep the notes is generally to make a sketch of the field and write along each line its length and bearing. See Fig. 22. 41. Form No. 3 is a modification of No. 2, and is mainly used in railroad surveying. The notes here shown are those for the preliminary survey described in Art. 37. Each principal station is denoted by a whole number, as explained in Art. 34, and each substation by an integer followed by a decimal, the integer denoting the number of the station immediately preceding, and the decimal, the number of feet from that station to the substation in question. Thus, Station 27.50 is the same as Station 27+50. Distances are given in hundreds of feet. Thus, the distance from 27.50 to 35.75, which is equal to (35.75 - 27.50) stations, is (8.25 x 100) feet, or 825 feet. COMPASS SURVEYING (PART 2) LATITUDE AND LONGITUDE RANGES DEFINITIONS AND GENERAL FORMULAS 1. Reference Lines.-For the purposes of platting and calculation, it is often convenient to locate all the points of a survey by their coordinates with reference to two coordinate axes perpendic ular to each other. In Fig. 1, TT' and GG' are two coordinate axes intersecting at O. The point P is located with reference to these axes by its perpendicular distances HP and H' P, or HP and OH, from GG' and TT', respectively. 2. In surveying, TT' usually represents a meridian, either true or mag netic, according as FIG. 1 the bearings of the courses are referred to the true or to the magnetic meridian. Such a meridian is called a reference COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS' HALL, LONDON meridian, or principal meridian, while the perpendicular G G', which is an east-and-west line, is called a reference parallel of latitude, or principal parallel of latitude. The reference meridian and parallel are generally, though not necessarily, taken through the most westerly corner or station of the tract surveyed. 3. Latitude and Longitude.-The latitude of a point is the distance of the point from the reference parallel of latitude. Latitudes are measured along north-and-south lines. In Fig. 1, the latitudes of the points P, P1, P, are, respectively, HP (= OH'), H, P. (= OH), and H,P, (OH). The latitude of a point is a north latitude or a south latitude according as the point is north or south of the reference parallel. For the purposes of combining latitudes by algebraic addition, north latitudes are considered positive, and south latitudes, negative. Thus, if HP is 360 feet, and H, P, is 525 feet, the latitude of P is said to be +360 feet, or simply 360 feet, while that of P, is said to be -525 feet. 4. The longitude of a point is the distance of the point from the reference meridian. Longitudes are measured along east-and-west lines. The longitude of a point is an east longitude or a west longitude according as the point is east or west of the reference meridian. East longitudes are considered positive; west longitudes, negative. In Fig. 1, the longitude of Pis H' P(OH), and that of P, is -HP, (= -OH1). 5. Beginning and End of a Line.-The point from which a line is run and measured is called the beginning of the line. The other extremity is called the end of the line. If, for instance, the line PQ, Fig. 1, is measured from P to Q, and its bearing is taken by sighting from P toward Q, then P is the beginning and Q the end of the line. If the line is run from Q to P, the beginning is Q, and the end, P. In the former case, the bearing of the line is N 30° E; in the latter, S 30° W. |