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Locating Points by Range Ties

A points location can also be determined by means of a RANGE TIE, using an angle and a

Figure 13-23.-Range ties.

distance. The method requires extra instrument manipulation and should be used only when none of the previous methods are satisfactory for use. Actually, range ties establish not only the corner of a structure but also the alignment of one of the sides. In figure 13-23, assume that the building is not visible from either A or B or that either or both of the distances from A to B to a corner of the building cannot be measured easily. With the instrument set up at either A or B and the line AB established, one member of the party moves along AB until he reaches point R, which is the intersection of line 1-2 extended. The instrument is moved and set up on R, and the distance along the line AB to R is measured. An angle measurement to the building is made by using either A or 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 by following given tie data. This tie data may be (1) a perpendicular offset distance from a single specified station, (2) angles from two stations, or (3) an angle from one station and the distance from another station.

Setting Points When Given a Perpendicular Offset Distance

To set a point when given an angle and its distance from a single station, you simply setup the instrument at the station, turn the designated angle, and chain the distance along the line of sight. For perpendicular offset, the angle is 90. To set a point when given a distance from each of two stations, you can manage by using two

Figure 13-24.-Locating a point by distances from two stations.

tapes if each of the distances is less than a full tape length. To do so, you set the zero end of the tapes on both stations, run out the tapes, and match the distance mark on each tape to correspond with the required distance from the stations. When the tape is drawn taut, the point of contact between the tapes will be over the location of the desired point.

If one or both of the distances is greater than a full tape length, you can determine direction of one of the tie lines by correct triangle solution. For example, in figure 13-24, you want to set Point B 120.0 ft from station A and 83.5 ft from station C. A and C are 117.0 ft apart. You can determine the size of the angle at A by triangle solution as follows:

To set point B, you can set up a transit at A, sight on C, turn 4114 to the left, and measure off 120.0 ft on that line of sight. As a check, you can measure BC to be sure it measures 83.5 ft.







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