CHAPTER 7 TRAVERSE Section I ... - GlobalSecurity.org

1 CHAPTER 7 TRAVERSES ection I. SELECTION OF TRAVERSEDEFINITION A TRAVERSE is a series of straight lines calledtraverse legs. The surveyor uses them toconnect a series of selected points calledtraverse stations (TS). The surveyor makesdistance and angle measurements and usesthem to compute the relative positions of thetraverse stations on some system of co-ordinates. STARTING CONTROL Since the purpose of a TRAVERSE is to locatepoints relative to each other on a commongrid, the surveyor needs certain elements ofstarting data, such as the coordinates of astarting point and an azimuth to an azimuthmark. There are several ways in which thestarting data can be obtained, and thesurveyor should make an effort to use the bestdata available to begin a TRAVERSE . Thedifferent variations in starting control aregrouped into several general Control Available Survey control is available in the form ofexisting stations with the station datapublished in a trigonometric list, or higherheadquarters may establish the station andprovide the station data.

2 The surveyor obtainsthe azimuth to an azimuth mark (startingdirection) by referring to a trigonometric listor computing from known Available When survey control is not available in thearea, the surveyor must assume the co-ordinate of the starting station. The assumeddata approximates the correct coordinate asclosely as possible to facilitate a map of the area is available, theapproximate coordinate of the startingstation is scaled from the map. (For surveypurposes, starting data scaled from a mapare considered to be assumed data.) Thesurveyor determines the starting direction byscaling it from the Maps Available When neither survey control nor maps areavailable, the coordinate of the starting pointis assumed. The surveyor determines thestarting direction by the most accurate FM 5-233 TYPES OF TRAVERSE Construction surveying makes use of twobasic types of TRAVERSE open TRAVERSE andclosed TRAVERSE An open TRAVERSE (figure 7-1) originates at astarting station, proceeds to its destination,and ends at a station whose relative positionis not previously known.

3 The open TRAVERSE isthe least desirable type of TRAVERSE because itprovides no check on fieldwork or startingdata. For this reason, the planning of atraverse always provides for closure of thetraverse. Traverses are closed in all caseswhere time TRAVERSE A closed TRAVERSE starts at a point and ends atthe same point or at a point whose relativeposition is known. The surveyor adjusts themeasurements by computations to minimizethe effect of accidental errors made in themeasurements. Large errors are closed on starting point. Atraverse which starts at a given point,proceeds to its destination, and returns to thestarting point without crossing itself in theprocess is referred to as a loop TRAVERSE (figure7-2). The surveyor uses this type of TRAVERSE toprovide control of a tract or parcel boundary,and data for the area computation within theboundary.

4 This type of TRAVERSE is also used ifthere is little or no existing control in the areaand only the relative position of the points loop TRAVERSE starts and ends on a station ofassumed coordinates and azimuth withoutaffecting the computations, area, or relativeposition of the stations. If, however, thecoordinates must be tied to an existing gridsystem, the TRAVERSE starts from a knownstation and azimuth on that system. Whilethe loop TRAVERSE provides some check uponthe fieldwork and computations, it does notprovide for a check of starting data or insuredetection of all the systematic errors thatmay occur in the closed on second known TRAVERSE closed on a second known pointbegins at a point of known coordinates, movesthrough the required point(s), and terminatesat a second point of known coordinates. Thesurveyor prefers this type of TRAVERSE becauseit provides a check on the fieldwork,computations, and starting data.

5 It alsoprovides a basis for comparison to determinethe overall accuracy of the 5-233 Section II. FIELD SURVEY FIELDWORK In a TRAVERSE , three stations are considered tobe of immediate significance. Surveyors referto these stations as the rear station, theoccupied station, and the forward rear station is the station from which thesurveyors performing the TRAVERSE have justmoved or a point to which the azimuth isknown. The occupied station is the station atwhich the party is located and over which theinstrument is set. The immediate destinationof the party is the forward station or the nextstation in horizontal angles, make instrumentpointings to the lowest visible point of thetarget which marks the rear and Measure the distance in a straight linebetween the occupied station and the forwardstation. Use horizontal taping procedures orelectronic distance measuring equipment.

6 TRAVERSE STATIONS Horizontal Angles The surveyor selects sites for TRAVERSE stationsAlways measure horizontal angles at theas the TRAVERSE progresses. The surveyoroccupied station by sighting the instrumentlocates the stations in such a way that at anyat the rear station and measuring theone station both the rear and forward stationsclockwise angles to the forward station. Toare visible. 7-3 FM 5-233 Selection of StationsIf the distance is measured with tape, the linebetween stations must be free of obstacles forthe taping team. The surveyor should keepthe number of stations in a TRAVERSE to aminimum to reduce the accumulation ofinstrumental errors and the amount ofcomputing required. Short TRAVERSE legsrequire the establishment and use of a greaternumber of stations and may cause excessiveerrors in azimuth because small errors incentering the instrument, in station markingequipment, and in instrument pointings aremagnified and absorbed in the azimuthclosure as errors in angle Markers TRAVERSE station markers are usually 2- by2-inch wooden stakes, 6 inches or more inlength.

7 The surveyor drives these stakes,called hubs, flush with the ground. The centerof the top of the hub is marked with asurveyor s tack or with an X to designate theexact point of reference for angular andlinear assist in recovering the station, thesurveyor drives a reference (witness) stakeinto the ground so that it slopes toward thestation. The surveyor must write theidentification of the station on the referencestake with a lumber crayon or china markingpencil or on a tag attached to the cloth may also be tied to the referencestake to further assist in identifying orrecovering the Signals A signal must be erected over survey stationsto provide a sighting point for the instrumentoperator and to serve as a reference for tapealignment by the taping team. The mostcommonly used signal is the range measuring angles, the surveyor placesthe tapered point of the range pole on thestation mark and uses a rod level to make thepole vertical for observations.

8 The surveyorshould check the verticality of the pole byverifying that the bubble remains centered atother points on the range pole. The range poleis maintained in a vertical positionthroughout the observation period either byuse of a range pole tripod or by someoneholding the pole. To prevent the measurementof angles to the wrong point, the surveyorplaces the range pole in a vertical positiononly when it is being used to mark a OF TRAVERSE PARTY The number of personnel available to performsurvey operations depends on the unit s Tableof Organization and Equipment (TOE). Theorganization of these people into a traverseparty and the duties assigned to each memberwill depend on the unit s Standing OperatingProcedure (SOP). The organization and dutiesof TRAVERSE party members are based on thefunctional requirements of the of the Party The chief of the party selects and marks thelocations for the TRAVERSE stations andsupervises the work of the other members ofthe party.

9 The chief of the party also assistsin the reconnaissance and planning of Operator The instrument operator measures thehorizontal angles at each TRAVERSE The recorder keeps the field notes (seeappendix B) for the party in a field notebook,and records the angles measured by theinstrument operator, the distances measuredby the tapeman, and all other data pertainingto the survey. The recorder is usually theparty member designated to check the tapeddistances by pacing between Two tapemen measure the distance from onetraverse station to the FM 5-233 Rodman The rodman assists the chief of the party inmarking the TRAVERSE stations, removes thetarget from the rear station when signaled bythe instrument operator, and moves the targetIt is possible to reduceforward to the next TRAVERSE number of personnelVariations in a TRAVERSE party,but there should beThe number of party members maybe reducedby combining the positions of party chief,two tapemen and a separateinstrument operator, and recorder.

10 It that one of the tapemen may doubleas a rodman, but it is best to have twotapemen and a separate rodman. Section III. COMPUTATIONS azimuth COMPUTATION The azimuth of a line is defined as thehorizontal angle, measured clockwise, from abase direction to the line in upon the starting data and thedesired results, the base direction used will begrid north. In extreme circumstances, theThe surveyor muststarting azimuth may even be a magneticdetermine an azimuthazimuth. In order for a TRAVERSE to becomputed, the surveyor determines anfor each leg of theazimuth for each leg of the TRAVERSE ( ).The azimuth for each succeeding leg of thetraverse is determined by adding the value ofthe measured angle at the occupied station tothe azimuth from the occupied station to therear station. The example which followsillustrates this procedure.