Figure 7-18.—Closed traverse with adjusted latitudes anddepartures.departures. Figure 7-18 shows a closed traverse withadjusted latitudes and departures notes. You want toassign plane coordinates to the traverse stations. Toavoid the necessity of working with negativecoordinates, you select as point of origin a point O thatis west of the most westerly traverse station and southof the most southerly traverse station.You determine the bearing and length of dotted lineOD and compute from these values the latitude anddeparture of OD. You can see that the Y coordinate ofstation D must equal the latitude of OD, or 150.70 feetAlso the X coordinate of D must equal the departure ofOD or 556.30 feet.The Y coordinate of station A equals the Ycoordinate of D plus the latitude of AD or150.70 + 591.64 = 742.34 ft.The X coordinate of station A equals the Xcoordinate of D minus the departure of AD or556.30 – 523.62 = 32.68 ft.The Y coordinate of station B equals the Ycoordinate of station A plus the latitude of AB or742.34 + 255.96 = 998.30 ft.The X coordinate of station B equals the Xcoordinate of station A plus the departure of AB or32.68 + 125.66 = 158.34 ft.The Y coordinate of station C equals the Ycoordinate of station B minus the latitude of C or998.30 – 153.53 = 844.77 ft.The X coordinate of station C equals the Xcoordinate of station B plus the departure of BC or158.34 + 590.65 = 748.99 ft.The Y coordinate of station D equals the Ycoordinate of station C minus the latitude of CD or844.77 – 694.07 = 150.70 ft.The X coordinate of station D equals the Xcoordinate of station C minus the departure of CD or748.99 – 192.69 = 556.30 ft.These are the same coordinates you originallycomputed for station D, a fact that serves as a check onyour accuracy.You enter these values on a form that is similar tothe one shown in figure 7-19. In actual practice,however, you will use a wider form on which all valuesand computations from the original station throughbearing and distance, latitude and departure, andcoordinates can be entered.LATITUDE AND DEPARTURE FROM PLANECOORDINATES.— The numerical values of latitudeand departure of a traverse line are easily computedfrom the coordinates of the end stations of the line. Fortraverse line AB, for example, the numerical value oflatitude equals the difference between the Y coordinateof A and the Y coordinate of B, while the numerical valueof departure equals the difference between the Xcoordinate of A and the X coordinate of B.To determine whether a latitude or departurecomputed this way is positive or negative, the bestmethod is to examine a sketch of the traverse todetermine the compass direction of the bearing of theline in question. If the line bears northeast, the latitudeis positive, or north, and the departure is positive, or east.If the line bears southwest, both latitude and departureare negative.Computing AreasVarious methods are used in computing areas. Someof the common methods with which the EA should befamiliar are discussed below.7-14
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business