and cultivated, or fields may have become overgrown or reforested. Gather and consider all available
information when searching for a station.
(1) Trig lists, control cards, and control bulletins contain brief descriptions and sketches of
stations. The information may be outdated or insufficient for a final product but will permit surveyors to
locate the general vicinity of the station. The final step in locating the station involves the use of
distances and azimuths from the reference marks (RMs) to the station.
(2) Previous survey data may include survey schemes, overlays, or plots depicting the relative
position of the stations in the general area. After one or more stations have been recovered, the other
stations may be roughly plotted and located using a magnetic compass and either intersection or
resection methods.
(3) Aerial photographs may be used if the station to be recovered can be identified in a
photograph. Using features that are permanent and prominent on both the photograph and the ground
will permit surveyors to reach the station site.
(4) Maps with the station's plotted coordinates permit surveyors to identify the route of travel to
the station. Maps also assist surveyors in determining the station's accessibility.
(5) Local information sources include local surveyors, public-service officials, construction
companies, and landowners. Local sources may be the only means of locating a station if the area has
dramatically changed since the other sources of information were published.
c. Verify a station before using it. In a situation where only one other station is intervisible, a
check-distance measurement can be performed using the GPS or a conventional method. When two or
more stations are intervisible, check-angle observations or GPS measurements can be performed. After
the measurements and observations have been performed and reduced, they will be compared to the
published information. If the results within the overall specifications for the survey project agree, the
stations may be used.
2-49. New Station Sites. New station sites will be selected after all existing stations have been
recovered, described, and verified. The new stations will be placed where required to complete the
scheme of the survey. The correct selection of a new station site will save time and expense and prolong
the life of the new station. Take the following factors into consideration when selecting a new station
site.
a. Monuments can be permanent or temporary.
(1) Permanent monuments are set in a relatively stable material or structure for the purpose of
preserving the location of either horizontal or vertical control. Consider another site if the proposed site
might experience disturbance or land development. Since there is a wide variety of possible situations
that may be
EN0593
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