Civil Engineering Reference
In-Depth Information
the angle to be turned would be 51° 42′ 26″ to the right. The same procedure
described above would be used to measure out 57.00 feet from the total station and
set the corner. Finally, the distance between points A and B should be checked.
This could be done by using a tape if the distance is relatively short. Alternately,
the total station could be set on A or B and the EDM used to check the distance. If
neither of these alternatives is possible, the angle and distance from 1 to B and 2
to A could be calculated and the total station used to measure the angles and dis-
tances to the points.
Setting lot corners is one area where a servo driven tracking total station really
pays for itself, particularly when there are many lot corners to set. Once the total
station and backsight are set up, the data collector is used to specify which point
needs to be set. The data collector will then cause the total station to automati-
cally turn in the direction of the point. Once the rod person is near the point, the
total station can be set to track the rod person and continually update the distance
and angle measurements. Listening to instructions from the instrument person, the
rod person can essentially walk to the lot corner. This is even easier with a robotic
total station or RTK GPS because the rod person would then have the data collec-
tor—usually attached to the prism pole. In this case the rod person can read off
the distance correction herself. For example, the data collector for a robotic total
station might display “Move 0.15′ Left and Go Out 0.67′”. Graphic data collectors
will also have an image of the point to be set and the location of the prism pole.
The person setting the point can then graphically see which way to move and how
far to move.
5.17 Some Commonly Used Surveying Techniques
Double Centering
. All surveying instruments have small errors which can affect
the accuracy of a survey. Instruments are calibrated to eliminate errors but some-
times small errors continue to exist. Let us consider an example where we need
to extend a straight line. Imagine that you are laying out a new airport runway
and you have been asked to place marks on the runway so that a centerline can be
painted. You only have two points. One point is in the middle of the pavement at
the approach end of the runway. The second point is in the middle of the pavement
halfway down the runway. This is shown in Fig.
5.16
. You need to establish a point
at the departure end of the runway.
You set up the instrument at the halfway point. You sight a point at the
approach end then, without touching the horizontal circle clamp or tangent screw,
you invert the telescope and sight the departure end of the runway. You have
Fig. 5.16
Double center
