OUTSIZED LATITUDE AND/OR DEPARTURE ERROR OF CLOSURE

Engineering Aid 2 - Intermediate Structural engineering guide book
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Figure 7-41.—Gaphical method to locate angular mistake in a closed traverse (see angle C). 107°42' along the way. You should look for an angle of about this size in the traverse. Suppose that in a four-sided traverse, the difference between the sum of the R-deflection angles and the sum of the L-deflection angles comes to 180°. For a four-sided traverse, this difference should be 360°. The larger difference suggests that you have given one of the angles a wrong direction. Look for an angle measuring about half the error of closure (in this case, measuring half of 180°, or 90°), and see whether you may have given this angle the wrong direction. If you have not dropped an angle, a large interior- angle error of closure probably means a large mistake in measuring or in recording the measuring of one of the angles. You may be able to locate the doubtful angle by plotting the traverse from the measured angles. ‘Then draw in the line of the linear error of closure and erect a perpendicular bisector from this line. The bisector may point to the dubious angle. For example: In figure 7-41, all the bearings are correct except the bearing of CD, which should be S15°31'W for closure, but inadvertently you made a mistake and have S05°31'W. Because of this error, the traverse fails to close by the length of the dotted line AA'. Figure 7-42.—Graphical method to locate angular mistake in a closed traverse (see angle A). A perpendicular bisector from AA' points directly at the faulty angle C. If a perpendicular bisector from the line of linear error of closure does not point at any angle, the faulty angle may lie at the point of the beginning of the traverse. In figure 7-42, the bearings of all lines are correct for closure except that of the initial line AB. Line AB should be N29°09'E for closure but was plotted N16°09'E. A perpendicular from AA' does not point at any angle in the traverse. OUTSIZED LATITUDE AND/OR DEPAR- TURE ERROR OF CLOSURE.— When both the latitudes and departures fail to close by large amounts, there is probably a mistake in an angle or a distance. When one closure is satisfactory and the other is not, a computational mistake is probably the cause of the outsized closure error. OUTSIZED LINEAR ERROR OF CLO- SURE.— When an angular error of closure is within allowable limits and there is an outsized linear error of closure, you should check for mistakes as follows: 1. Ascertain that you have not dropped a traverse line. 2. Ascertain that each latitude and departure is in the correct column. 7-28

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