Presentation Concepts v2

8/7/2019 Presentation Concepts v2

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Concepts


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Plane survey(Plane angle)

Geodetic survey(Sphericalangle)

Triangulationsurvey

Traverse survey

Closed traverse(Includedangles)

Looped

Connecting

Open traverse(Deflectionangles)

Total survey

GPS

Laser survey

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Ext ri r angle

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L ped Stati nA is Fixed C nnecting Stati ns A & B are Fixed

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Foresight line

Prolongation of backsight line

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?

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The bearing ofaline isthe direction of the linewith respect to a givenmeridian. A bearing is

indicated by thequadrant in which the

line falls and the acuteangle that the linemakes with themeridian in that

quadrant.

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Theazimuth (or bearing) from A to B ( ) is determined by reducing the observed azimuth to therelative quadrant. In Figure, if the azimuth from Point A to the Azimuth Mark is 320, and observedangle "" from Station A between the reference azimuth point and Point B is 105, then the azimuthof the line from Point A to Point B "" is computed from:

Azimuth ( ) from A B = 105 - (360 - 320) = 65 [or bearing N 65 E ]

The computation of the difference in northing (dN) and the difference in easting (dE) requires thecomputation ofa right triangle. The distance from Station A to Station B ("s" in Figure, reduced tohorizontal, sealevel, corrected for grid scale, etc.) is the hypotenuse of the triangle, and thebearing angle (azimuth) is the known angle. The following formulas are used to compute dN and

dE: dN = s cos () dE = s sin ()8


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Differences in elevation are measured with respectto a horizontal line of sight established by theleveling instrument.

Once the instrument is leveled (using either a spiritbubble or automated compensator), its line ofsight lies in a horizontal plane.

Leveling comprises a determination of the

difference in height between a known elevationand the instrument and the difference in heightfrom the instrument to an unknown point bymeasuring the vertical distance with a precise orsemi-precise level and leveling rods.

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Applies the fundamentals of trigonometry to

determine the differences in elevation

between two points by observing horizontaldistance and

verticalangles above or below a horizontalplane

Trigonometric leveling is generally used for

lower-order accuracy vertical positioning.

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Trigonometric elevations over longer lines may needto be corrected for curvature and refraction.

Corrections are insignificant (< 0.02 ft) and

unnecessary for topographic survey distances of1,000feet or less. Wolfand Brinker formula is used to determine the

combined curvature and refraction correction fortrigonometric elevations observed over longer lines.

h = 0.0206 (F)2

whereh = combined correction for curvature and refraction in feet and

F= length of observed line in thousands of feet

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Uses the differences in atmospheric pressureas observed with a barometer or altimeter to

determine the differences in elevationbetween points. Least accurate of determining elevations. Should only be used when other methods are

not feasible or would involve great expense. Generally, this method is used for elevations

when the map scale is to be 1:250,000 orsmaller.

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Carrying alevel circuit across an area over

which it is impossible to run regular

differentiallevels with balanced sights. Most level operations require aline of sight to

be less than 300 or 400 feet long.

May be necessary to shoot 500-1,000 feet, or

even further, in order to span across a river,canyon, or other obstacle.

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3-wire leveling are short cross lines thatcannot be mistaken for the long centralline used for ordinary leveling.

The rod is read at each of the three lines and

the average is used for the final result.Before each reading, the level bubble is

centered.The half-stadia intervals are compared to

check for blunders.

Upper Wire: 8.698 2.155 :Upper IntervalMiddle Wire: 6.543

Lower Wire: 4.392 2.151 :Lower Interval

Sum 19.633 Difference = 0.004 only

Average 6.544 18


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International Terrestrial ReferenceFrame (ITRF). North American Datum of 1983 (NAD 83).

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Retro-reflectorprisms

Extendable

rods 20 feetand above

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Reference Base Remote (Rover)

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3D Laser Scanner Laser scanned and Rendered Image

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Rules WCB RB Quadrant

1 0 - 90 = WCB - 0 NE

2 90 - 180 = 180 - WCB SE3 180 - 270 = WCB - 180 SW

4 270 - 360 = 360 - WCB NWN

W E

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Rules RB WCB Quadrant

1 0 - 90 = RB - 0 NE

2 90 - 180 = 180 - RB SE3 180 - 270 = RB + 180 SW

4 270 - 360 = 360 - RB NWN

W E

S 33


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Direction of survey line

Bearing (direction relative to any meridian) or

Angle with relation to another line

Bearings

True meridian (with imaginary line betweengeographical north and south poles)

Magnetic meridian (direction shown by a freelysuspended magnetic needle)

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Thank you

Presentation Concepts v2

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