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ERE (EXTRA REGIMENTAL
EMPLOYEES) 371 Exam 2 Standardized
2025 Questions With Full Answers
Upgraded A.
Traverse
Series of lines of known length connected at traverse stations, related by known angles. Stations must have visibility to next and previous station.
Traversing
Activity of establishing and measuring traverse. Applied as common method for local horizontal control surveys.
Mathematically Closed Traverse
- Geometrically closed : polygon that begins and ends on same point. Checks: angular measurements
- Geometrically open : begin/end on different points. point locations known better than measurements. Control station on both ends. Checks: angles and distances.
Mathematically open traverse
Begin and end on unrelated pts. Control station on only 1 end. No checks/ closure so must repeat measurements. Application: exploratory surveys
Interior angles
usually turn CW. Checks: measure exterior angle or (n-2)*
Deflection Angles
Measure L or R from prior direction. Used for geometrically open (e.g. route). Sight backsight and then turn angle to foresight.
Distance methods
Stadia, taping, EDM. Varies in accuracy/ time/ cost. Geo open = stationing, Geo closed = measure lines individually. Often EDM is used to meet standards.
Stationing
Identify key pts along route. Show distance from pt of beginning (POB)
"Full stations" use 100 ft / 1000 m increments and "Pluses" between full stations (i.e. POB: station 0+00, 1+11.2 = 111.2 feet along route from POB)
Hubs / Traverse Stations
location depends on purpose of survey - mapping vs. construction vs. property. Issue of accuracy, utility, & efficiency. Must be intervisible, and maximize line length. Permanent or relocatable.
Referencing traverse station
measured with different accuracy.
- determine preliminary line directions
- calc deps/lats
- calc preliminary station coordinates
- adjust measurements
- calc adjusted station coordinates
- calc adjusted lengths and directions of lines
Traverses can be open or closed, both mathematically and geometrically. Explain the
distinction between these types of traverses.
Mathematically closed traverses begin and end on points that are known. In the case of a
mathematically and geometrically closed traverse, the beginning and end points are the same; in the
case of a mathematically closed, but geometrically open traverse, the beginning and end points are
known relative to each other, but are not the same. A mathematically open traverse begins and ends
on points that have no known relationship; therefore, mathematically open traverses must also be
geometrically open since they end on a different point from where they began.
A route survey begins on station 100+00, then proceeds 159.60 ft to point A, and from
there 312.12 ft to point B. Compute the stationing for point A and point B.
Each full station is 100 feet counted along the route, thus point A is at station 101+59.60 and point B
is at station 104+71.72.
Describe an issue in selecting the location of traverse station. How might this issue vary
depending on the application of the control network under development?
Any reasonable answer is acceptable here; ideas discussed in class include accuracy, utility, efficiency,
intervisibility, and permanence. These issues might have slightly different resolution depending on
the type of survey that will subsequently be performed, e.g., mapping vs. construction vs. cadastral. If
a traverse is being performed to map a region, then the primary features need to be visible from at least
one traverse station; if the survey is for construction, issues with permanence in any area that is
undergoing change become critical; for cadastral surveys, the property corners much be visible from
one of the traverse points.
Describe the purpose of traverse computations. What are the underlying assumptions that
should be met before performing traverse adjustment?
Traverse computations are used to check if required accuracy is met, to adjust a traverse to get
geometric consistency and to compute control point locations. Performing traverse adjustment does
not make a traverse better or more accurate, just more consistent. Traverse adjustment should only be
applied when systematic errors and mistakes have been removed and the remaining random errors are
normally distributed and fall within the error tolerance that is appropriate for the survey application.
Three approaches to adjustment were discussed in class: arbitrary, compass rule, and least squares.
Traversing Errors/Mistakes
Personal error: poor station location related to line of sight. Angle/Distance measurement errors can be personal, instrumental, or Natural. Mistakes include set up of instrument/back/foresight, and notetaking
local horizontal i.e., it is perpendicular to gravity at a point and tangent to the geoid at a point.
However, the plane is not necessary tangent to the ellipsoid or the actual Earth surface. The use
of a plane for a reference surface is appropriate for small extents, particularly with lower
accuracy specifications.
Geoid
equipotential gravitational surface, i.e., it has equal gravitational potential at all
points. The geoid is perpendicular to gravity everywhere. Mean sea level is a common example
of a geoid. The geoid is mathematically undefined, but is observable and is commonly used for
vertical reference surfaces.
Ellipsoid
mathematical surface obtained by revolving an ellipse about polar axis. The
dimensions of the ellipse are typically selected to provide the closest fit to the geoid. The
ellipsoid is mathematically defined, and is commonly used for global, or continental, horizontal
reference surfaces.
Plane
defined using
local horizontal i.e., it is perpendicular to gravity at a point and tangent to the geoid at a point.
However, the plane is not necessary tangent to the ellipsoid or the actual Earth surface. The use
of a plane for a reference surface is appropriate for small extents, particularly with lower
accuracy specifications.
Describe a consequence of ignoring earth curvature when making measurements of horizontal
distance
the difference between a direct line connecting two points and the great
circle connecting two points is insignificant for relatively long distances i.e. only a 6mm
difference over 8 km. However, the discrepancy is more significant as distances become much
larger, e.g. over 1000km there is more than a 1 km difference between a straight line distance
and a great circle distance.
Describe a consequence of ignoring earth curvature when making measurements of vertical distance
the difference between a horizontal plane and a level surface is measurably
different at relatively short distances, e.g. at a mile out, the separation is approximately 8 inches.
Describe a consequence of ignoring earth curvature when making measurements of horizontal angles.
in a plane triangle, angles sum to 180°. This holds true for triangles of area
up to approximately 75 sq. miles, at which point because of earth curvature, the angle sum is
increased by one second.
Describe the Universal Transverse Mercator Coordinate system, including origin, projection
characteristics and coordinate components. What are the advantages and disadvantages of using
Explain why grid and geodetic azimuths at a point are typically not the same.
The UTM and State Plane coordinate systems select a central meridian for a zone, and then
create a rectangular grid with all grid meridians parallel to the central meridian. Along the
central meridian, grid and true azimuths will be the same, but as you move away from the central
meridian, the convergence of the true meridians toward the North Pole mean that the true north
meridian is not parallel to the grid meridian, thus directions relative to the two different systems
will not be the same.
Arbitrary adjustments
essentially distribute angular and distance error using no particular justification.
It would be hard to find any scenario where this would be justifiable.
