surveying iii (topographic and geodetic surveys) - Modern Prepper

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5-43. Loop Closure Checks. Postprocessing criteria are aimed at an evaluation of a single baseline.To verify the adequacy of a group of connected baselines, one must perform a loop closure on thebaselines formulated. When GPS baseline traverses or loops are formed, their linear (internal) closureshould be determined in the field. If the job requires less than third-order accuracy (1:10,000 or 1:5,000)and the internal loop/traverse closures are very small, a formal (external) adjustment may not bewarranted.a. The internal closure determines the consistency of the GPS measurements. Internal closures areapplicable for loop traverses and GPS networks. It is required that one baseline in the loop beindependent. An independent baseline is observed during a different session or on a different day.Many of the better postprocessing software packages come with a loop closure program. Refer to themanufacturers' postprocessing user's manual for the particulars of the loop closure program includedwith the hardware. If the postprocessing software package does not contain a loop closure program, theuser can perform the following loop closure computation:Step 1. List the ΔX, ΔY, ΔZ, and the distance components for all baselines used in the loop closure.Step 2. Sum the ΔX, ΔY, ΔZ, and the distance components for all baselines used in the loop closure.Step 3. Add the square of each of the summations together and take the square root of this sum.This resultant value is the misclosure vector for the loop.Step 4. The loop misclosure ratio is calculated as follows:Loop misclosure ratio = m/LWhere--mL= misclosure for the loop= total loop distance (perimeter distance)The resultant value can be expressed as 1:loop misclosure ratio. All units for the expressions are statedin terms of the units used in the baseline formulations (such as meters, feet, or millimeters).b. External closures are computed in a manner similar to internal loops. External closures provideinformation on how well the GPS measurements conform to the local coordinate system. Before theclosure of each traverse is computed, the latitude, the longitude, and the ellipsoid height must beconverted to geocentric coordinates (X, Y, and Z). If the ellipsoid height is not known, geoid-modelingsoftware can be used with the orthometric height to get an approximate ellipsoid height. The externalclosure aids the surveyor in determining the quality of theEN0593 5-40
known control and how well the GPS measurements conform to the local network. If the controlstations are not of equal precision, the external closures will usually reflect the lower-order station. Ifthe internal closure meets the requirements of the job, but the external closure is poor, the known controlis probably deficient and an additional known control point should be included in the system.5-44. Data Archival. The raw data is the data recorded during the observation period. Raw datashould be stored on an appropriate medium (such as a compact disk, a portable hard drive, or magnetictape). The raw data and the hard copy of the baseline reduction (resultant baseline formulations) shouldbe stored at the discretion of each unit's command.PART G - ADJUSTING PRECISE-POSITIONING SURVEYS5-45. General. Differential carrier phase GPS-S observations are adjusted the same as conventionalsurvey observations. Each 3D GPS baseline vector is treated as a separate distance observation andadjusted as part of a network. A variety of techniques may be used to adjust the observed GPS baselinesto fit existing control. Since GPS-S networks often contain redundant observations, they are usuallyadjusted by some type of rigorous least squares minimization technique. This section describes some ofthe methods used to perform horizontal GPS-S adjustments and provides guidance in evaluating theadequacy and accuracy of the adjustment results.5-46. Global Positioning System Error Measurement Statistical Terms. To understand theadjustment results of a GPS-S, it is necessary to understand the following statistical terms: Accuracy. Accuracy is how close a measurement or a group of measurements is in relation toa true or known value. Precision. Precision is how close a group or sample of measurements is to other groups orsamples. For example, a low standard deviation indicates high precision. A survey or groupof measurements can have a high precision but a low accuracy (for example, measurementsare close together but not close to the known or true value). Standard Deviation. Standard deviation is a range of how close the measured values are fromthe arithmetic average. A low standard deviation indicates that the observations ormeasurements are close together.5-47. Adjustment Considerations. This section deals primarily with the adjustments of horizontalcontrol established using GPS observations. Although vertical elevations are carried through thebaseline reduction and adjustment process, the relative accuracy of these elevations is normallyinadequate for engineering and construction purposes. Special techniques and constraints are5-41 EN0593
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SUBCOURSEEN0593EDITIONAUNITED STATE
Page 3 and 4:
TERMINAL LEARNING OBJECTIVE:ACTION:
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Part G: Adjusting Precise-Positioni
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PART A - FIGURES OF THE EARTH1-1. T
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Figure 1-2. Flattening Fractiona. T
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1-3. Geoid. In geodesy, precise com
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point in the survey to provide the
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one side of a triangle and all of t
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Figure 1-10. Simple Triangulation N
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observation, contains a light sourc
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of a horizontal rod with a small sp
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The Airy theory, announced by G. B.
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Figure 1-15. Products of the Gravim
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a. If the shape of the earth was ex
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Figure 1-16. Single Astronomic Stat
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Figure 1-17. Astro-Geodetic Deflect
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Figure 1-19. Astro-Geodetic Datum O
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(c) The significance of a gravity-o
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absolute deflections of the vertica
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Figure 1-23. Preferred Datumsa. The
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1-17. The World Geodetic System. Be
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Figure 1-25. Using the Same Referen
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LESSON 1PRACTICE EXERCISEThe follow
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12. Which of the following is assum
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LESSON 1PRACTICE EXERCISEANSWER KEY
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THIS PAGE IS INTENTIONALLY LEFT BLA
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for all military and civilian activ
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i. Additional support for other top
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2-7. Status. At present, topographi
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in both. (North American Datum of 1
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water can impede leveling operation
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A field recording booklet. A single
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PART I - OFFICE WORK2-24. General.
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PART J - SURVEY COMMUNICATION2-28.
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length or side is known, and all th
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second-order, Class I net. The leng
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The number of observations required
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to perform the reconnaissance. Fail
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and cultivated, or fields may have
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e an alphanumeric symbol that is st
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2-53. Intervisibility of Stations.
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station is (K/2) 2 x 0.0676, or one
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Figure 2-8. Similar Triangles Solut
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2-54. Height of Obstructions. It is
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authorized to change the name, it s
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Figure 2-12. Cells Connected in Par
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added as the cells weaken. Three un
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Figure 2-16. Construction Details f
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2-60. Wooden Towers. When it become
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11. The face of the 5-inch signal l
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average line in a triangulation sys
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3-4. Slope Measurements. The slope
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strip as close as possible to its f
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. Sight along the tops of both of t
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Column 1. Record the station number
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stake to steady it. With the back o
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Figure 3-3. DA Form 4446 (Sample of
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micrometer in this optical system i
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laterally across the front of the e
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Figure 3-7. Horizontal Circle and M
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out of adjustment. If the index mar
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(1) In order to avoid instrumental
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location of the vertical circle on
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Figure 3-13. Open Traversec. Closed
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designate the exact point of refere
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example, a line with an azimuth of
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When adjusting a traverse that star
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11. The unit of graduation on a hor
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THIS PAGE IS INTENTIONALLY LEFT BLA
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differential leveling. The theodoli
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additional runs are made due to exc
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Figure 4-2. Wild N-3 Precision Leve
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(8) Loosen the azimuth clamp (13),
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4.7. Miscellaneous Equipment. In ad
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(2) To check for gross errors in th
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(a) (1) Begin by completing the inf
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Set up and level the instrument. Re
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Figure 4-8. Sun and Wind Code(5) Th
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(10) Enter the interval between the
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Figure 4-9. Closed-Circuit River Cr
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Figure 4-11. Sample DA Form 5820 (R
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is 0. When the telescope is pointed
Page 176 and 177: stations. However, since all statio
Page 178 and 179: a. Complete the heading, as shown.b
Page 180 and 181: a. (1) Enter the date, as in the sa
Page 182 and 183: LESSON 4PRACTICE EXERCISEThe follow
Page 184 and 185: 11. The maximum length of site to o
Page 186 and 187: LESSON 4PRACTICE EXERCISEANSWER KEY
Page 188 and 189: PART A - GLOBAL POSITIONING SYSTEM
Page 190 and 191: 5-7. Pseudorange. A pseudorange is
Page 192 and 193: 5-15. Number of Pseudorange Observa
Page 194 and 195: i. Probable Error Measures. The acc
Page 196 and 197: Table 5-1. Representative GPS Error
Page 198 and 199: Table 5-2. Carrier Phase Trackinga.
Page 200 and 201: exercise extreme caution in applyin
Page 202 and 203: not be designed or performed to ach
Page 204 and 205: Table 5-3. GPS-S Design, Geometry,
Page 206 and 207: f. Multiple/Repeat Baseline Connect
Page 208 and 209: possible ionospheric and tropospher
Page 210 and 211: Figures 5-4. PDOP Versus Time PlotP
Page 212 and 213: e. Field Processing and Verificatio
Page 214 and 215: All carrier phase relative-surveyin
Page 216 and 217: time spent and the cost of conducti
Page 218 and 219: movement between occupation sites,
Page 220 and 221: 5-37. General. GPS baseline solutio
Page 222 and 223: (1) Receiver Time. This technique u
Page 224 and 225: NOTE: Repeated baselines should be
Page 228 and 229: necessary to determine approximate
Page 230 and 231: This will ensure that future work w
Page 232 and 233: may (and usually does) far exceed t
Page 234 and 235: important in evaluating the overall
Page 236 and 237: i. Relative GPS baseline standard e
Page 240 and 241: 12. When the networking method is s
Page 242 and 243: LESSON 5PRACTICE EXERCISEANSWER KEY
Page 244 and 245: THIS PAGE IS INTENTIONALLY LEFT BLA
Page 246 and 247: FAR-77 obstructions. Aircraft-movem
Page 248 and 249: Figure 6-1. Imaginary SurfacesEN059
Page 250 and 251: Figure 6-3. Approach Surfacesa. Fed
Page 252 and 253: . Federal Aviation Regulation-77, S
Page 254 and 255: Table 6-4. Airport Obstruction Accu
Page 256 and 257: A horizontal scale of 1:12,000 and
Page 258 and 259: Figure 6-4. Sample DA Form 5821 (Ai
Page 260 and 261: Figure 6-5. Sample DA Form 5822 (PA
Page 264: LESSON 6PRACTICE EXERCISEANSWER KEY
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