Civil Engineering Reference
In-Depth Information
it by the total station. Typically the person running the total station points the tel-
escope at the target and presses a button on the data collector. The data collec-
tor instructs the EDM to measure the distance. Once the distance is measured, the
horizontal and vertical angles and the distance are transmitted to the data collector
where the information is stored in memory. If the data collector is connected to
a GPS receiver, the coordinates and elevation of the point are stored in memory.
When the field crew returns to the office, the data is electronically transferred
from the data collector to a desktop computer. Now, with the increased use of cell
phones and data storage in the cloud, the field data could be made available to the
office, which could be hundreds of miles away, in real time.
Data collectors normally record two basic types of data. The first data type con-
sists of the
Raw Data
which is collected by the total station. For a total station this
includes the horizontal angle, slope distance and vertical angle. The data collector
will also store the name of the backsight, occupied point and foresight. This will
be explained in more detail in the section on using a total station to measure an
angle. Raw data is often stored in an ASCII text file which can be read by most
word processors or a simple text editor on a personal computer.
In addition to the raw data file the data collector calculates and stores the 3
dimensional coordinates of the point, the name or number of the point and a
description of the point. Coordinate files are often proprietary binary files which
usually cannot be read with a word processor. The purpose of keeping a raw data
file is that the file is a record of every measurement which is taken in the field.
Even if the coordinate file were to become lost or corrupted it would be possible to
regenerate it using the raw data file.
5.12 Field Topics
The information in the raw data ile could also be written in a ield topic. Before
data collectors became available, ield topics were the commonly accepted way
of recording data. When ield topics were used, mistakes were sometimes made
reading the angle or distance from the instrument, transposing numbers or writing
incorrect information into the topic. Because the data is transferred automatically,
data collectors have largely eliminated these errors. On the down side, it is not
unheard of for data collectors or inexperienced users, to mess up and lose data
that may have taken hours or days to collect. This can't happen with a ield topic,
although it is possible that someone could lose it. For certain surveys where evi-
dence must be admissible into court it may still be preferable, or even essential, to
have a written record of the ield work, so, under these circumstances, a ield topic
would still be necessary.
As already noted, before data collectors became available, ield topics were
the only way to record measurements. Field topics are usually hard cover, bound
topics which are small enough (6″ 8″) to it in a large pocket. The pages are
usually bound in pairs with one side having lined columns and a facing page with
