Figure 13-23.-Range ties.Figure 13-24.-Locating a point bystations.distances from twodistance. The method requires extra instrumentmanipulation and should be used only when noneof the previous methods are satisfactory for use.Actually, range ties establish not only the cornerof a structure but also the alignment of one ofthe sides. In figure 13-23, assume that the buildingis not visible from either A or B or that either orboth of the distances from A to B to a corner ofthe building cannot be measured easily. With theinstrument set up at either A or B and the lineAB established, one member of the party movesalong AB until he reaches point R, which is theintersection of line 1-2 extended. The instrumentis moved and set up on R, and the distance alongthe line AB to R is measured. An angle measure-ment to the building is made by using either Aor B as the backsight. The range distance, R-2,is measured as well as the building dimensions.SETTING ADJACENT POINTS“To set a point adjacent to a traverse line”means to establish the location of a point byfollowing given tie data. This tie data may be(1) a perpendicular offset distance from a singlespecified station, (2) angles from two stations, or(3) an angle from one station and the distancefrom another station.Setting Points When Givena Perpendicular Offset DistanceTo set a point when given an angle and itsdistance from a single station, you simply setupthe instrument at the station, turn the designatedangle, and chain the distance along the line ofsight. For perpendicular offset, the angle is 90°.To set a point when given a distance from eachof two stations, you can manage by using twotapes if each of the distances is less than afull tape length. To do so, you set the zero endof the tapes on both stations, run out the tapes,and match the distance mark on each tape tocorrespond with the required distance from thestations. When the tape is drawn taut, the pointof contact between the tapes will be over thelocation of the desired point.If one or both of the distances is greater thana full tape length, you can determine direction ofone of the tie lines by correct triangle solution.For example, in figure 13-24, you want to setPoint B 120.0 ft from station A and 83.5 ft fromstation C. A and C are 117.0 ft apart. You candetermine the size of the angle at A by trianglesolution as follows:To set point B, you can set up a transit at A,sight on C, turn 41°14´ to the left, and measureoff 120.0 ft on that line of sight. As a check, youcan measure BC to be sure it measures 83.5 ft.Setting Points When GivenAngles from Two StationsTo set a point when given the angle from eachof two traverse stations, you should ordinarily13-19
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