Page 67 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.17

A range pole is a convenient accessory in line and angle work. It is a pole 7 or 8 feet long,
equipped with a metal point. It is painted alternately red and white in bands 1 foot wide. It is
lighter than a rod and because of its conspicuous pattern is more readily seen at a distance.
This pole is set on one of the lines in question. The instrument is swung so that the vertical
crosshair is on the pole. The rotation is locked, and the hair lined exactly on the pole by turning
the horizontal tangent screw.
The reading on the horizontal circle and on the vernier is recorded.
The pole is placed on the other line and sighted in the same way. The difference between the
two readings is the angle between the lines.
Line and angle work may be done to stake out on the ground locations described on a blueprint
or map; or to make a record of ground features or locations on paper so that they may be used in
figuring, or replaced or relocated if necessary.
Staking out is best left to surveyors if possible, as accurate work involves trigonometry and skill-
ful use of the instrument, and inaccurate work may result in very expensive mistakes. However, in
emergency, or when results need be only approximate, contractors can do it themselves.
Staking from a Map. An example of staking out from a map is shown in Fig. 2.14. A building,
25 40 feet, is to be erected at the location shown on a plot 100 feet square. Lot corner stakes
are at A and B.
The instrument is set up on A and sighted at B. The distances AA″ and A″B″ are measured
along the line of sight, and stakes driven at A″ and B″. The instrument is then set up on A″, sighted
on B, and turned 90°. The distances A″C and CE are measured and stakes put at C and E.
The transit is now set on C, sighted at A″, and turned 90°, the distance CD measured, and a
stake placed at D. Point F is located from the instrument set at E in the same manner. The instru-
ment is now set on F, sighted at E, and turned 90°, measuring the distance to D and B″ for a check
on the accuracy of the work. The amount of error allowable will depend on job requirement.
This technique is practical for the amateur only on square or rectangular lots. Another method,
which is applicable to any lot for which two widely spaced locations may be found both on the
map and in the lot, is illustrated in Fig. 2.15. The house is located on the plot plan, and lines are
drawn from the known corners A and B to the near corners of the building, as shown. These lines
are measured and converted to feet according to the scale, and the angles they make with line AB
and with each other are measured with a protractor. Figures are written on the plan.

FIGURE 2.14 Locating house site. FIGURE 2.15 Locating house site in irregular plot.