2 Introduction to Surveying Definition:Surveying is the science and art of determining the relative positions of points above, on, or beneath the earth’s surface and locating the points in the field.
3 The work of the surveyor consists of 5 phases: Decision Making – selecting method, equipment and final point locations.Fieldwork & Data Collection – making measurements and recording data in the field.Computing & Data Processing – preparing calculations based upon the recorded data to determine locations in a useable form.Mapping or Data Representation – plotting data to produce a map, plat, or chart in the proper form.Stakeout – locating and establishing monuments or stakes in the proper locations in the field.
4 2 Categories of Surveying: Plane Surveying – surveying with the reference base for fieldwork and computations are assumed to be a flat horizontal surface.Generally within a 12 mile radius the pull of gravity is very nearly parallel to that at any other point within the radius and thus horizontal lines can be considered straight.Geodetic Surveying – surveying technique to determine relative positions of widely spaced points, lengths, and directions which require the consideration of the size and shape of the earth. (Takes the earth’s curvature into account.)
5 7 Types of Surveys:Photogrammetry – mapping utilizing data obtained by camera or other sensors carried in airplanes or satellites.Boundary Surveying – establishing property corners, boundaries, and areas of land parcels.Control Surveying – establish a network of horizontal and vertical monuments that serve as a reference framework for other survey projects.Engineering Surveying – providing points and elevations for the building Civil Engineering projects.
6 7 Types of Surveys:Topographic Surveying – collecting data and preparing maps showing the locations of natural man-made features and elevations of points o the ground for multiple uses.Route Surveys – topographic and other surveys for long – narrow projects associated with Civil Engineering projects.Highways, railroads, pipelines, and transmission lines.Hydrographic Surveying – mapping of shorelines and the bottom of bodies of water.Also known as bathymetric surveying.
7 Brief History of Surveying: Surveying had it’s beginning in Egypt about 1400 BCLand along the Nile River was divided for taxation. Divisions were washed away by annual floods.“ROPE-STRETCHERS” Egyptian surveyors were created to relocate the land divisions (measurements were made with ropes having knots at unit distances).Extensive use of surveying in building of Egyptian monumentsGreeks: expanded Egyptian work and developed Geometry.Developed one of the earliest surveying instruments – Diopter (a form of level).
8 Brief History of Surveying: Romans: developed surveying into a science to create the Roman roads, aqueducts, and land division systems.Surveyors held great power, had schools and a professional organizationDeveloped several instruments:Groma – cross instrument used to determine lines and right anglesLibella – “A” frame with a plumb bob used for levelingChorobates – 20’ straight edge with oil in notch for levelingMiddle Ages: land division of Romans continued in Europe.Quadrans – square brass frame capable of turning angles up to 90° and has a graduated scale developed by an Italian named Von Piso.
9 Brief History of Surveying: 18th & 19th Century in the New World: the need for mapping and marking land claims caused extensive surveying, especially by the English.1785: United Stated began extensive surveys of public lands into one mile square sections30 states surveyed under the U.S. Public Land System (also called the Rectangular System)1807: United States Geological Survey founded to establish an accurate control network and mappingFamous American Surveyors: George Washington, Thomas Jefferson, George Rogers Clark, Abe Lincoln and many more.
10 Brief History of Surveying: 20th Century and Beyond: As technology advanced, population increased, and land value caused development of licensure for surveyors in all states.Educational requirements for licensure began in the early 1990’sCapable of electronic distance measurement, positioning using global positioning systems, construction machine control, and lidar (scanning) mappingInvolvement in rebuilding of the infrastructure and geographic information systems (GIS)Shortage of licensed professionals is projected well into the 21st century
11 Measurement of Distance Linear measurement is the basis of all surveying and even though angles may be read precisely, the length of at least one line in a tract must be measured to supplement the angles in locating points.Methods of measuring a horizontal distance:Rough Measuring: Pacing, Odometer readings, Tacheometry (stadia), Taping, EDM, and GPSOnly the last three meet survey accuracy requirementsDistance from stadia: (High wire-Low wire) * 100 = Distance (ft)More accurate measuring: taping, EDM (1966), GPSEDM and GPS are most common in today’s surveysIn pacing, one establishes the # of paces/100’ by counting the # of paces over a pre-measured 300’ line
12 Measurement of Distance Taping: applying the known length of a graduated tape directly to a line a number of times.2 Problems exist in Taping:Measuring the distance between two existing pointsLaying out a known distance with only the starting point in place
13 Measurement of Distance 6 Steps of TapingLining in – shortest distance between two points is a straight line.Applying tension – rear chain is anchor and head chain applies required tension.Plumbing – horizontal distance requires tape to be horizontal.Marking tape lengths – each application of the tape requires marking using chaining pins to obtain total length.Reading the tape – the graduated tape must be read correctly.Recording the distance – the total length must be reported and recorded correctly.
14 Types of Chains and Tapes Before the ability to make steel rods and bands, sticks were cut into lengths of 16.5’ (Rod) and they were laid end to end to measure.Gunter’s Chain66’ long with 100 link w/each link being 7.92 inches or 66 feet longDeveloped by Edmund Gunter in 1600’s in England and made with individual wires with a loop at each end connectedChain had between wearing surfaces which with hard use would wear and cause chain to elongateMeasurements were recorded in chains and links7ch 94.5lk = ch = X 66’/ch = ’1 chain = 4 rods; 80 chains = 1 mile
15 Types of Chains and Tapes Engineer’s ChainSame construction as Gunter’s Chain, but each link is 1.0’ long and was used for engineering projectsSurveyor’s and Engineer’s TapesMade of ¼” to 3/8” wide steel tapes in 100’; 200’; 300’ lengthsMultiple types of marking and graduation:Available in chains, feet, and metricGraduated:Throughout – feet and tenths marked the entire lengthExtra foot – feet marked the length of the tape with additional foot at the 0 end graduated in tenths and hundreds of the foot
16 Types of Chains and Tapes Invar TapesMade of special nickel steel to reduce length variations due to temperature changesThe tapes are extremely brittle and expensiveUsed most of the time for standard comparison of tapesCloth, Fiberglass, and PVC Tapes:Lower accuracy and stored on reels. Used for measurement of 0.1’ accuracy requirementsAccessoriesChaining Pins – set of 11, used to mark the tape lengthsHand Level – used to determine required plumbing heightPlumb Bob – used to transfer the mark from the tape to groundTension Handle – used to maintain correct tension on tape
17 Taping (Field Process) The line to be taped should be marked at both endsKeeps measurement on lineRear chain person should keep the head chain person on line1’ of line error/100’ = 0.01’ error in lengthApplying TensionRear chainman is anchor and should hold 100’ mark over pointTension is applied by head chain person – normally 12 to 30 pounds of pullTapes are standardized at 12 lbs., but greater is utilized to compensate for sag
18 Taping (Field Process) PlumbingOne end of tape is raised to maintain a horizontal measuring plane. ONLY one end is elevatedThis allows measurements to be made on uneven groundIf a high spot exists in center, “break” tape by measuring to the top and then move forward to complete the distance
19 Slope Measurements:Generally, measurements are made horizontally, but on even, often man-made slopes the distance can be measured directly on the slope, but the vertical or zenith angle must be obtained.Horizontal Distance = sin Zenith Angle X Slope DistanceHorizontal Distance = cos Vertical Angle X Slope Distance
20 Stationing:Starting point is 0+00 and each 100’ is one station 700’ from starting point is Station 7+00If distance is ’ from starting point, it is expressed as Station
21 Taping Error:Instrumental Error – a tape may have different length due to defect in manufacture or repair or as the result of kinksNatural Error – length of tape varies from normal due to temperature, wind and weight of tape (sag)Personal Error – tape person may be careless in setting pins, reading the tape, or manipulating the equipmentInstrumental and natural error can be corrected mathematically, but personal error can only be corrected by remeasure.When a tape is obtained, it should either be standardized or checked against a standard.Tapes standardized at National Bureau of Standards in MarylandStandardized at 68 degrees F and 12 lbs. tension fully supported.
22 Tape Error Correction: Measuring between two existing points:If a tape is long, the distance will be short, thus any correction must be addedIf tape is short, the distance will be long, thus any correction must be subtractedIf you are setting or establishing a point, the above rule is reversed.Generally can correct for tape length, temperature, tension, and sag, but tension and sag are negated by increasing tension to approximately 25 – 30 lbs.
23 Error in Taping: Tape Length: Correction per foot = Error in 100’/100’ If tape was assumed to be ’ but when standardized was found to be ’ after distance measured at ’then: Correction =( )/ = ’ error/ft565.75’ X .0002’/’ = 0.11’ correction and based upon rule, must be added, thus true distance = ’If tape had been 99.98’ then correction would be subtracted and true distance would be ’
24 Error in Taping:Temperature – Tapes in U.S. are standardized at 68F; the temperature difference above or below that will change the length of the tapeTapes have a relatively constant coefficient of expansion of per unit length per FCT = (Temp (F)-68) LengthExample: Assume a distance was measured when temperature was 30°F using a 100’ tape was ’ (68 – 30) X X ’ = 0.21’ error tape is short, thus distance is long, error must be subtracted and thus ’ – 0.21’ = ’(note: temperature difference is absolute difference)
26 TransitTransit is the most universal of surveying instruments – primary use is for measurement or layout of horizontal and vertical angles – also used to determine vertical and horizontal distance by stadia, prolonging straight lines, and low-order leveling.3 Components of the TransitAlidade – Upper partHorizontal limb – Middle partLeveling-head assembly – Lower part
27 Transit Alidade (upper part) Circular cover plate w/2 level vials and is connected to a solid conical shaft called the inner spindle.Contains the vernier for the horizontal circleAlso contains frames that support the telescope called STANDARDSContains the vertical circle and its verniers, the compass box, the telescope and its level vial
30 Transit Horizontal Limb (middle part) This is rigidly connected to a hollow conical shaft called the outer spindle (which holds the inner spindle)Also has the upper clamp, which allows the alidade to be clamped tightAlso contains the horizontal circle
32 Transit Leveling-Head Assembly (lower part) 4 – leveling screws Bottom plate that screws into tripodShifting device that allows transit to move ¼ to 3/8”½ ball that allows transit to tilt when being leveledThe SPIDER – 4-arm piece which holds the outer spindleLower clamp – allows rotation of outer spindle
34 Telescope: Similar to that of dumpy level, but shorter Parts – objective, internal focusing lens, focusing wheel, X-hairs, & eyepieceScales: horizontal plate or circle is usually graduated into 30’ or 20’ spaces with graduations from 0 to 360 in both directionsCircles are graduated automatically by machine and then scanned to ensure accuracyThey are correct to with in 2” of arc
35 VerniersLeast count = Lowest # of reading possible – determines accuracyLeast Count = (Value of smallest division on scale)/(# of divisions on vernier)Scale GraduationVernier DivisionsLeast Count30’301’20’4030”15’4520”10’6010”
37 Verniers 3 Types of Verniers Direct or single vernier – reads only in one direction & must be set with graduations ahead of zeroDouble vernier – can be read clockwise or counterclockwise–only ½ is used at a timeFolded vernier – avoids a ling vernier plate½ of the graduations are placed on each side of the index markUse is not justified because it is likely to cause errors
38 VerniersThe vernier is always read in the same direction from zero as the numbering of the circle, i.e. the direction of the increasing anglesTypical mistakes in reading verniers result fromNot using magnifying glassReading in the wrong direction from zero, or on the wrong side of a double vernierFailing to determine the least count correctlyOmitting 10’, 15’, 20’, 30’ when the index is beyond those marks
40 Properties of the Transit Designed to have proper balance between:Magnification and resolution of the telescopeLeast count of the vernier and sensitivity of the plate and telescope bubblesAverage length of sight of 300’ assumed in designSpecifications of typical 1’ gun:Magnification – 18 to 28XField of view - 1 to 130’Minimum focus – 5’ to 7’X-hairs usually are + with stadia lines above and belowThe transit is a repeating instrument because angles are measured by repetition and the total is added on the plateAdvantages of this:Better accuracy obtained through averagingDisclosure of errors by comparing values of the single and multiple readings
41 Handling the Transit Hints on handling and setting-up the transit Pick up transit by leveling head and standardsWhen carrying the transit, have telescope locked in position perpendicular to the leveling head with objective lens downWhen setting-up, keep tripod head level and bring plumb bob to within ¼” of point to be set over, then loosen leveling screws enough to enable you to move transit on plate, then move transit until it is over the point
42 Operation of Transit 9 Steps BC9 StepsSet up over point B and level it. Loosen both motionsSet up the plates to read 0 and tighten the upper clamp. (Upper and lower plates are locked together)Bring Vernier to exactly 0 using upper tangent screw and magnifying glass.Sight on point A and set vertical X-hair in center of point, by rotating transitTighten the lower clamp and entire transit is locked inSet X-hair exactly on BS point A using the lower tangent screws. At this point the vernier is on 000’ and the X-hairs are on BS
43 Operation of TransitABCLoosen the upper clamp, turn instrument to right until you are near pt. C. Tighten the upper clampSet vertical X-hair exactly on pt. C using the upper tangent screw.Read on vernierIf repeating , loosen lower motion and again BS on A (using only lower motion), and then loosen upper motion to allow to accumulate.If an instrument is in adjustment, leveled, exactly centered, and operated by an experienced observer under suitable conditions, there are only 2 sources for error.Pointing the telescopeReading the plates
44 Transit Field Notes Use longest side for backsite 1d Mean 0-90 90-180(4d + 360) 4180-270(4d + 720) 4270-360(4d ) 4Use longest side for backsite
46 TOTAL STATION SET UPWHEN TOTAL STATION IS MOVED OR TRANSPORTED, IT MUST BE IN THE CASE!!!!!!!!ESTABLISH TRIPOD OVER THE POINT.OPEN THE CASE AND REMOVE TOTAL STATION, PLACING IT ON THE HEAD OF THE TRIPOD AND ATTACH SECURELY WITH CENTER SCREW.CLOSE THE CASE.GRASP TWO TRIPOD LEGS AND LOOK THROUGH THE OPTICAL PLUMB, ADJUST THE LEGS SO THAT BULLSEYE IS OVER THE POINT (KEEP THE TRIPOD HEAD AS LEVEL AS POSSIBLE).UTILIZING THE TRIPOD LEG ADJUSTMENTS, LEVEL THE TOTAL STATION USING THE FISH-EYE BUBBLE.LOOSEN THE CENTER SCREW TO ADJUST THE TOTAL STATION EXACTLY OVER THE POINT IF NEEDED.COMPLETE LEVELING THE TOTAL STATION USING THE LEVEL VIAL.CHECK TO MAKE SURE YOU ARE STILL ON THE POINT.
47 TURNING ANGLES WITH TOTAL STATION SIGHT ON THE BACKSIGHT UTILIZING THE HORIZONTAL ADJUSTMENT SCREW.ZERO SET THE INSTRUMENT (THIS PROVIDES AN INNITIAL READING OF0 SECONDS.LOOSEN TANGENT SCREW AND ROTATE INSTRUMENT TO FORESIGHT.TIGHTEN TANGENT SCREW AND BRING CROSS HAIR EXACT ON TARGET WITH ADJUSTMENT SCREW.READ AND RECORD ANGLE AS DISPLAYED.TO CLOSE THE HORIZON:SIGHT ON FORESIGHT POINT FROM ABOVE AND ZERO SET INSTRUMENT.ROTATE TO FORMER BACKSIGHT AND ADJUST INSTRUMENT TO EXACT.ANGLE FROM DIRECT AND INDIRECT SHOULD EQUAL 360 DEGREES.
48 TOTAL STATION DISTANCE MEASUREMENT POINT THE INSTRUMENT AT A PRISM (WHICH IS VERTICAL OVER THE POINT.PUSH THE MEASURE BUTTON AND RECORD THE DISTANCE.YOU CAN MEASURE THE HORIZONTAL DISTANCE OR THE SLOPE DISTANCE, IT IS IMPORTANT THAT YOU NOTE WHICH IS BEING COLLECTED.IF YOU ARE MEASURING THE SLOPE DISTANCE, THE ZENITH ANGLE MUST BE RECORDED TO ALLOW THE HORIZONTAL DISTANCE TO BE COMPUTED.IF YOU ARE COLLECTING TOPOGRAPHIC DATA WITH ELEVATIONS, IT IS IMPORTANT THAT THE HEIGHT OF THE INSTRUMENT AND THE HEIGHT OF THE PRISM BE COLLECTED AND RECORDED.THIS CAN ALSO BE SOLVED BY SETTING THE PRISM HEIGHT THE SAME AS THE INSTRUMENT HEIGHT.
49 TOTAL STATION RULESNEVER POINT THE INSTRUMENT AT THE SUN, THIS CAN DAMAGE THE COMPONENTS OF THE INSTRUMENT AS WELL AS CAUSE IMMEDIATE BLINDNESS.NEVER MOVE OR TRANSPORT THE TOTAL STATION UNLESS IT IS IN THE CASE PROVIDED.DO NOT ATTEMPT TO ROTATE THE INSTRUMENT UNLESS THE TANGENT SCREW IS LOOSE.AVOID GETTING THE INSTRUMENT WET, IF IT DOES GET WET, WIPE IT DOWN AND ALLOW TO DRY IN A SAFE AREA BEFORE STORAGE.BATTERIES OF THE TOTAL STATION ARE NICAD AND THUS MUST BE CHARGED REGULARLY. AT LEAST ONCE PER MONTH, THE BATTERY SHOULD BE CYCLED.CARE SHOULD BE TAKEN AT ALL TIMES, THESE UNITS ARE EXPENSIVE ($8,000 - $45,000)
50 Angles and Determination of Direction Angle – difference in direction of 2 linesAnother way of explaining is the amount of rotation about a central point3 kinds of Horizontal angles: Exterior ( to right); Interior; DeflectionTo turn an angle you needA reference lineDirection of turningAngular distanceAngular UnitsDegrees, minutes, seconds (sexagesimal system)Circle divided into 360 degreesEach degree divided by 60 minutesEach minute divided into 60 secondsRadians1 radian = 1/2 of a circle = *360 = 5717’44. 8”Grads (Centesimal System) – now called Gon1/400 of a circle or 054’00” (100 gon = 90)
51 Angles and Determination of Direction Angles turned in field must be accurate: 3X least count is max. errorCheck #1 – Close horizon when turningIf traverse closes: sum of the interior angles should equal the sum of(N-2)X180, N = Number of sides3 angles = (3-2) 180 = 1804 angles = (4-2) 180 = 3608 angles = (8-2) 180 = 108025 angles = (25-2) 180 = 4140If an exterior angle exists, subtract it from 360 to obtain the interior Angular closure should be checked before leaving the field
52 Angles and Determination of Direction If angular adjustment does not divide out equally:Do not go to decimal unless instrument reads to decimalObserve field notes for angles with poor closure or where problems turning angles existed. Apply excess to these angles evenly.If unable to view field notes or no apparent source, generally apply excess to angles with shortest sidesBearings/AzimuthsBearing of a line is the acute horizontal angle between a reference meridian (North and South) and a lineAzimuth of a line is the horizontal angle measured from the North meridian clockwise to the line
54 Angles and Determination of Direction 4 Point ComparisonBearingAzimuth1. Numeric Value0-900-3602. Method of Expressing2 letters & numberNumber only3. DirectionClockwise & counterclockwiseClockwise4. Position of 0 pointNorth and SouthNorthIt is always very important to have your field sketch properly oriented
55 Angles and Determination of Direction Rectangular CoordinatesTotally based on computation of right triangleNorth – South Movement = Latitude = D X cos AEast – West Movement = Departure = D X sin ALatitude running North are +, South are –Departure running East are +, West are –
56 Angles and Determination of Direction Basic ProcedureDetermine Latitude and DepartureSum Lat. and Departure to calc. closureObtain balanced Lat. and Dept. (Compass Rule)Determine coordinatesOnce rectangular coordinates are known on point, their exact location is known with respect to all other points in the network
58 Angles and Determination of Direction Balancing MethodsCompass Rule: (Bowditch) Used when accuracy of and length measurement is equal(Error Lat./Perimeter length) X Distance = Latitude Correction(Error Dept./Perimeter length) X Distance = Departure CorrectionTransit Rule: Used if angles are more accurate than distances (more accurate direction)Correction Latitude (Side) = (Lat. Side/Sum all Lat.) X Lat. errorCorrection Departure (Side) = (Dept. Side/Sum all Dept.) X Dept. errorCrandall Method: Used when larger random error exists in linear measurements that angular. Directional adjustments from balancing are held fixed and distances are balanced by a weighted least squares procedureLeast Squares: Based on the theory of probability. Angular and linear adjustments are made simultaneously. Hand methods are long and complex not often done. Computer adjustment through existing software make it feasible, which is why it is often used today
59 Area, Inverse, Intersection Once rectangular coordinates are established on all points, the relationship to all other points is known. You can:Determine area of all or any portionDetermine length and direction between any 2 pointsLocate new points by intersection
60 Area, Inverse, Intersection Area: Method is area by cross multiplicationUsing example from traverse lecture:NA X EB + NB X EC + NC X ED + ND X EE + NE X EF + NF X EA = Sum NEA X NB + EB X NC + EC X ND + ED X NE + EE X NF + EF X NA = Sum EDifference in Sums/2 = Square feetSquare feet/43560 = AcresABCDEFSum N = 294,119,678.8Sum E = 293,663,353.6456,325.2 / 2 = 228,162.6 ft2 = 5.24 Ac
61 Area, Inverse, Intersection Example: Determine Area of A, D, E, F, AADEFN = 186,116,759.8E = 185,971,439.3145,320.5 / 2 = 72, ft2 = 1.67 Ac
62 Area, Inverse, Intersection Inverse: With known coordinates of any two points on a system, you find the distance and direction between the twoCDTo find the Inverse between 2 PointsFind difference in N & E of coordinatesPlotUse point you are going from 1stPlot longest side 1stDetermine length using Pythagorean (a2 + b2 = c2)Determine reference directionDetermine local using tan A = a/bDetermine line direction
63 Area, Inverse, Intersection Example: Determine direction and distance D-ADA
64 Area, Inverse, Intersection Intersection: Determination of unknown point location with directions from two points knownDetermine difference in coordinatesPlot points and line projectionsSet up dual formulas (as Latitude and Departure)Solve for lengthCompute coordinate as sideshotCD
65 Area, Inverse, Intersection Example: What are the coordinates of the point of intersection of line C-F and D-A.Azimuth D-A = 3834’46”.Coordinates of D: N = , E =CF
66 Horizontal and Vertical Curves Horizontal curves are the basis for most Right of Ways:Go through formulasAngle at PC and PT are always 90Given any 2 elements T, L, C, R, D; the remainder can be completedExample: Horizontal curve, PC STAD = 3615’00”R = ’T =L =C =Seg =PI STA =PT STA =
67 Horizontal and Vertical Curves Vertical Curves – Two major methods used to calculate vertical curves: Tangent offset and Equation of ParabolaInformation needed:Grade or slope on each side of curveElevation and station of PVICurve length (Horizontal distance PVC – PVT)
68 Horizontal and Vertical Curves Tangent Offset MethodProcedure:Compute the elevation of the PVC and PVTCompute the elevation of Chord midpointCompute offset to curve at midpointDetermine total number of stations coveredDetermine tangent elevations at stationsCompute curve offset at stationsCombine data and determine vertical curve elevations
69 Horizontal and Vertical Curves Equation of Parabola MethodEquation: r = g2 - g1 / Lg1 = initial grader = change in grade/sta.g2 = final gradeL = length of curve in stationsProcedure:Compute PVC and PVT elevationsCalculate total change in grade/stationInsert data to chart and compute final curve elevationsTo find the elevation at the high point or low point,find the station at which it fall and include thatstation in the elevation computationsThe equation gives the distance from the PVC in stations
70 LevelingLeveling is the determination of the elevation of a point or difference between points referenced to some datumTerms:Datum – any level surface to which elevations are referencedMean Sea Level (MSL) – the average height of the surface of the sea for all stages of the tide over a 19 year period at 26 tide stations along Pacific, Atlantic and GulfNational Geodetic Vertical Datum – nationwide reference surface for elevations throughout the U.S. – made available by National Geodetic Survey (NGS), based on 1929 adjustment.Benchmark – relatively permanent object bearing a marked point whose elevation above or below an adopted datum.
71 Leveling Most often Mean Sea Level is used MSL varies along the coastsPacific is almost 2’ higher than Atlantic and GulfU.S. System: National Geodetic Vertical Datum of 1929Has been used as reference for extensive network of BM’sBM’s are periodically adjusted as to elevationBest to check with USGS or NGS for current elevation of a BM and also best to check between two known BM’s to verify elevation difference.
72 LevelingThe level surface parallels the curvature of the earth a level line is a curved line, normal () at all points to plumblineLine of sight is only normal at point of instrumentA line with a sight distance of 1 mile using the earth’s radius as 3959 mile, curvature change is feet.Refraction of line of sight of level is downward by a small amountThe combined curvature & refraction amounts for short distances (normal sight dist. for levels) are:100’ = ’200’ = ’300’ = ’500’ =Value is small for most instances can be neglected
73 LevelingMost common leveling instrument today is the Automatic or Self-leveling level – has an internal compensator that automatically provides a horizontal line of sight and maintains this through gravity (prism hanging on pendulum)Differential Leveling: (Spirit Leveling) Most common type todayDetermine the difference in elevation using a horizontal line of sight and readings on graduated rodCircuit must be closed on BM of origin or on BM of equal accuracyProcess:Reading on point of known elevation (BS)BS reading + BM elevation = HIReading on point of unknown elevation (FS)HI – FS = elevation of new point
74 Leveling Systematic Error in Leveling Inclination of line of sight due to curvature of earth and refraction – generally very minimal due to short sightsInclination due to maladjustment of instrumentBoth can be alleviated by equalizing length of BS and FS legsChanges in scale of rod due to temperatureUsually ignored except in very precise workWould use same process as tape correctionRod not held plumbMinimized by carefully plumbing the rod or more commonly known as “Rocking the Rod” and taking the lowest reading
75 LevelingPeg TestSet 2 marks at 300’ apart, also mark center point in a relatively flat areaSet level at midpoint and take readings at each endDetermine difference in readings (difference in elevation)Move level to one end and setup so that level is just in front of rod on pointRead rod by looking backward through scope (X-hair not visible), hold pencil on rod to determine readingRead rod at other end in normal mannerDifference in readings should equal #3If values are not equal, there is errorMost instruments have adjustment screwsAdjust and repeat test as a check
76 Seven Basic Rules of Differential Leveling Balance length of BS and FS (300’ max)Make sure gun is level and pendulum freeTurn through all BM’sGive complete description of BM’s and TBM’sHave rod rockedMake sure turning points are solidClose all circuits on BM of same degree of accuracy
77 Other Random ErrorsIncorrect rod reading – most common viewing foot number above and recording itParallax – having the X-hair not properly focusedHeat Waves – limit shot lengths
78 Field Notes STA BS HI FS ELEV Sum BS – Sum FS = Difference of Elevation
79 Closure Error Difference in measured elevation and know elevation Correction factor = closure / # turnsError = 0.09’Turns = Correction = ’ / turnIf TBM’s set, break circuit into sectionsFigure correction factor the sameFigure correction by taking CF X # turns in section
80 Precise LevelingPrecise Leveling – Accuracy obtained by quality of instruments and care taken in the fieldHigh quality automatic levels are utilizedLevel rods are equipped with rod level, rod shoe (to allow better setting on BM’s); scale (on rod) is made of invar steel (not affected by temp – generally called Invar Rod)Reading either taken by optical micrometer or a process called 3-wire leveling is used (all 3 wire are read and averaged)Optical micrometer: line of sight deflected by turning micrometer screw to read subdivision on rod.Rod division is read as normal & then fractional reading taken from micrometer screw, thus on normal rod readings to ’ are possible
81 Topographic Surveying Topographic surveying is the process of determining the positions, on the earth’s surface, of the natural, and artificial features of a given locality and of determining the configuration of the terrain.Planimetry – location of featuresTopography – configuration of the groundBoth produce a topographic map which shows the true distance between objects & their elevations above a given datumTopos can be done by field methods, or by photogrammetric methods. (Photo also requires some field work)Topo map is 1st step in a construction project
82 Topographic Surveying Scale and accuracy: Both depend on what used forMethod of Representing:Most common is Contour Line – Imaginary line on surface of the earth passing through points that have equal elevationContour Interval – Vertical distance between linesTopo map with contour lines shows elevation of points on ground & shapes of topographic features (hills, etc.)USGS Topo – 10’ or 20’ contour intercalSubdivision – 2’ or 4’Index Contour – every 5th contour drawn heavier on mapsSlopes & X-sections can be obtained from contours
83 Topographic Surveying Interpolating – can find elevation of any point or find contour line with known elevation of pointContour lines that close represent either a hill or depression and can be represented as:Marks are called hatchures (used most in depressions)
84 Characteristics of Contours Each contour must close upon itself with within a map or outside its borders – a contour line cannot end on a map except at the edgeContours do not cross or meet except in caves, cliffs & vertical walls where they can meetContour lines crossing streams form V’s pointing upstreamContour lines crossing a ridge form U’s pointing down the ridgeContour lines tend to parallel streams
85 Characteristics of Contours Contour lines are uniformly spaced on uniform slopesHorizontal spacing between contour lines indicated steepness of slope on groundContours are generally perpendicular to direction of maximum slopeContours can never branch into 2 contours of the same elevation
86 Field Methods of Topos Factors That Influence Method Scale of map Contour intervalType of terrainNature of projectEquipment availableRequired accuracyExisting controlExtent of area to be mapped
87 Field Methods of Topos Methods: Cross section – railroad of highway Trace contour – drainage or impoundmentsGrid – small areasControlling point – large area, plane tableTheodolite & EDM - radial
88 Field Methods of Topos Cross Section Method (Plus Offset): Equipment used: Transit, tape, and levelEstablish horizontal control – traverse between control points – stakes set at cross section intervalsRun profile of traverse lineTake cross sectionLocate planimetric features from traverse line
89 Field Methods of Topos Trace Contour: Contour is by traverse Establish elevation of each stationContour elevation established and is then followed by rodpersonContour elevation is marked, then tied to traverse line by plus-offsetMost accurate and expensive workElevation of reservoir water line2 transit use
90 Field Methods of Topos Grid Method: Establish baselines Estimate grid of uniform size – smaller grid = more accurateNumber gridShoot elevation at each pointTie existing objects to grid points
91 Field Methods of ToposControlling Point Method: (old and sketched in field)Determine position & elevation of pre-selected control pointsDepends greatly on experience & judgment of people doing workRequired traverse of area (CP’s)Locations are made & elevations obtained along control points – then intermittent topo sketched in
92 Field Methods of Topos Theodolite & EDM (Radial) Replaces tacheometry (stadia)Establish control points (horizontal and elevation)Shoot locations and turn vertical anglesUsed for large areas
93 Field Methods of Topos Common mistakes in topo surveys: Improper selection of contour intervalUnsatisfactory equipment or field method for the particular survey and terrain conditionsInsufficient horizontal and vertical control of suitable precisionOmission of some topographic details
94 Mine Surveying Points are on roof of mine Reasons needed Location in respect to boundariesLocation in respect to other shaftsAccurate maps (above and below ground)QuantitiesEquipment and TermsSpad – Beams that you hold plumb bob fromBracket – Mounting instrument from timber supportsTrivet – Tripod that’s about 1’ tallGyroscope – Locate northLaser vertical collimator – located point at top of vertical shaft platformPlumb shaft – Using piano wire then wiggle in at bottom
95 Global Positioning Systems (GPS) Developed in early 1980’ s (Dept. of Defense)Made up of 26 satellites (24 functioning & 2 spares)Each satellite is 20,000 km high (off Earth’s surface)Each satellite is in a fixed positionMinimum of 3 satellites needed, but 4-5 preferredNeed satellites at least 15° above horizonLocate positions on Earth by distance-distance intersectionNeed 2-3 receivers ($80-$100K per system)Most accurate with double occupancy (no other checks)Differential GPS – one receiver on known point, other receiver on unknowns
96 Global Positioning Systems (GPS) Biggest advantageDistance and direction in-between 2 points without being seenDownfalls/Limitations of GPSMultipath – bouncing off of walls of buildingsBlocked signals – clouds, trees, etc.Sunspot – defraction from atmosphereDOP (Delusion of Position) – bad satellite positionSet up error – not set up exactly over point (human error – most common)
97 Global Positioning Systems (GPS) MethodsStatic – observation time is at least an hourIdeally set points in triangular fashionAccuracy – 1/10 millionRTK (Real Time Kinematic) – stand for seconds minimumBase receivers transmission, does corrections, sends corrections to receiversLimitations – limitation of transmitter signal
98 Geographic Information Systems (GIS) GIS are computer programs that allow users to store, retrieve, manipulate, analyze and display spatial dataSpatial Data (Geographic data) – any data that represents information about the EarthGIS componentsRecent definitions of GIS suggest that is consists of:Hardware (computer and operating system)SoftwareDataHuman Operators and Institutional InfrastructureGeographic/SpatialNon-Geographic/Aspatial/Attribute
99 GIS Data StructuresVector – Made up of points, lines, and polygons
100 GIS Data StructuresRaster (Grids) – Made up of pixels of computer screen
101 GIS Data StructuresDEM (Digital Elevation Model) – Digital terrain representation technique, where elevation values are stored in raster cells
102 Future of Surveying Major advances in future Design Professions Remote Sensing (Government and Military)Arial PhotographsDesign ProfessionsEvery 10 years, must justify to Legislature that need for our license existsSurveyor have ULTIMATE liabilityStandards → LawsContinuing Education – Enough points every 2 years