2 Finding a suitable location to set up the GPS base station T – Bar Setup (Permanent)Fixed Height Tripod Setup(Mobile )
3 The Do’s Location that is preferably central to the project Base Station as high as possibleBase Station receiver does not lose powerLocation that can easily be reproducedProtected and Secure locationSet up the GPS base station in a location that is preferably central to the projectsite, so that it can deliver RTK corrections over the radio for the maximum rangein all directions.• Set up the GPS base station as high as possible, so that the GPS antenna is clearfrom obstructions, and so that the radio antenna delivers the best possibletransmission for the maximum possible range.• Make sure that the base station receiver does not lose power. It can be poweredby its internal batteries or, by an external 12 V power supply or AC power. Forpermanent installations, AC power (also known as mains power) is preferable.The internal battery will always charge from AC power and thereby provides anuninterruptible power supply in times of AC power failure.• Establish the base station at a location that can easily be reproduced if thereceiver is likely to be taken down at the end of operations each day. The mosteffective means of creating a reproducible location is to build a T-Bar (seehere).Place the GPS receivers in a protected and secure location. If the base station isin the center of a jobsite where heavy machinery is operating, place flags aroundthe base station to warn operators of its existenceTrimble recommends that you install lightning protection equipment atpermanent base station locations. A static dissipater near the antennas can reduce the likelihoodof a direct lightning strike. Also protect any communications and power lines atbuilding entry points.Trimble recommends that you use surge protection equipment on allpermanently installed equipment.
4 The Don’ts Radio transmission equipment Trees Tall Buildings Ponds Overhead power linesElectrical generation facilitiesDo not locate a GPS receiver, GPS antenna, or radio antenna within 400 meters(about 1,300 feet) of:– a powerful radar, television, or cellular communications tower– another transmitter– another GPS antennaCell phone towers can interfere with the base station radio broadcast and canstop corrections from reaching the rover receiver. High-power signals from anearby radio or radar transmitter can overwhelm the receiver circuits. This doesnot harm the receiver, but can prevent the receiver electronics from functioningcorrectly.Low-power transmitters, such as those in cell phones and two-way radios, donot interfere with receiver operations.Do not place the GPS antenna near vertical obstructions such asbuildings, deep cuttings, site vehicles, towers, or tree canopyDo not set up the base station directly beneath or close to overhead power linesor electrical generation facilities. The electromagnetic fields associated withthese utilities can interfere with GPS receiver operation. Other sources ofelectromagnetic interference include:– Gasoline engines (spark plugs)– Televisions and computer monitors– Alternators and generators– Electric motors– Equipment with DC-to-AC converters– Fluorescent lights– Switching power supplies
7 Operation Modes Basic Features Basic+ Features Full Features designed to meet the needs of those site users who require minimal functionalityBasic+ Featuresenables the site supervisor to establish the base station, enter control point coordinates and then carry out a site calibration in addition to using all the features in the Basic Features operation modeFull Featuresall the features availableBasic Features operation mode – This mode provides a very simple version ofthe SCS900 software, which is designed to meet the needs of those site userswho require minimal functionality. A skilled operator can set up a site and thenleave a basic system for a less-skilled operator to use. Typically, a site supervisoror foreman can use the Basic Features operation mode every day on the samesite, enabling them to review digital design information and view real-time cutand fill data. The log file capability enables them to start to record informationfor simple as-built grade checks on the site, once grading operations arecomplete.• Basic+ Features operation mode – This mode enables the site supervisor toestablish the base station, enter control point coordinates and then carry out asite calibration in addition to using all the features in the Basic Featuresoperation mode.• Full Features operation mode – This mode contains all the features available inthe SCS900 software.The software is installed with all features. While selecting an operator name, the usercan select a login type that controls which functions are available to them. There is nosecurity associated with this login process; it is simply a mechanism to control whichfeatures the operator can access.
9 Main Menu Structure SCS900 software Is Two main functions menu-driven systemease of use and learningaccess to six submenusTwo main functionsMeasurementsStakeout1. Measurements – This function enables youto measure and record the location, oras-built location, of features or surfaces orobjects on a project, or to collectinformation that allows you to create asurface model, from which you can makevolume computations, and grade or materialthickness checks.2. Stakeout – This function enables you tostake or relocate any aspect of the siteincluding point features (such as manholes),line features (such as curbs, foundations, andfootings), planar surface features (such aspads), or surfaces (such as site terrainmodels, side slopes and catch points, or roadsurface models).
10 Work Orders menu Work Orders menu New Open Change Design Complete Work OrderExport/Import DataThe Work Orders menu contains the tools to create, open, and complete work orders.The menu also provides the capability to change the design referenced by the currentwork order, and output new design data from the current work order, for example, theoriginal ground topographic measurements.New –Create a new work order in the field as required for arequested task, for which no work order has been provided.The SCS900 software creates a new work order that referencesa specific site and design.Open-Open an existing work order. This can be:• a new work order, created by the supervisor, which you areto carry out• an in-progress work order, which you need to retrieve datafrom or add data to• a previously completed work order, which you need toreopen to retrieve information or to add information toChange Design-Select a different design, which provides different informationto that currently loaded, as a result of a change in the designfor the project, or a request to do something within thecurrent work order that requires different design data.Complete Work Order-Complete the currently open work order and write theWork-Order Measure.dxf file.Export/Import Data-Write the surface data that was measured in the field to a newdesign surface; export the site calibration file to aCompactFlash card; export a design to a CompactFlash card foruse with the GCS900 Grade Control System, save sitecalibration data to a memory card; and send or receive filesfrom “intelligent” s.
11 Measurement menu Measurement menu Check Surface Grade Check Grade of RoadwayCheck Material ThicknessMeasure SurfaceMeasure Site FeaturesDisplay Real-Time Cut/FillAdvanced MeasurementsThe Measurement menu contains all site measurement functions. With the dedicatedfunctions, you can check grades and material thickness, take topographicmeasurements to create surface models ( for example, volume computations), take sitefeature measurements to record the location of non-surface features, and providereal-time cut/fill information against a selected design model.Before you enter this menu, set up the system using the System Setup menu. If you donot, when you select an option in this menu, the software automatically puts youthrough either the station establishment process ( for a total station) or the rover setup( for GPS).Check Surface Grade-Check the grade of a surface against a selected design. Thisoption is available only when the current design is not a road.Check Grade of Roadway –Specify a high or low tolerance for the finished grade andcheck whether or not the grading operations have achievedtolerance.This option is available only when the current design is a road.Check Material Thickness-Check the thickness of laid materials against the specifiedthickness.Measure Surface-Measure a surface: points, break-lines, volume boundaries, andthe site boundary.Measure Site Features-Measure site features not used in the creation of a surface.Display Real-Time Cut/Fill-Check current cut and fill at any location on the project againstthe original ground, finished design, or any other surface.Advanced Measurements-Scanning options for use with total stations, specifically forscanning stockpiles or recording profile lines of objects likequarry walls or high walls. Automated point measurementenables prisms or targets to be repeatedly measured to checkfor movement, and s can notify users of movementoutside of the set tolerance.
12 Stakeout menu Stakeout menu Point Line Side Slope & Catch Point Plane Surface / RoadEnter/Edit Stakeout PointsThe Stakeout menu contains all SCS900 stakeout functions including staking points,lines and alignments, planes, surfaces, side slopes, catch points, and road features.Before you enter this menu, set up the system using the System Setup menu. If you donot, when you select an option in this menu, the software automatically puts youthrough either the station establishment process ( for a total station) or the rover setup( for GPS).Point-Stake individual point data. The software guides you directly tothe point.Line-Stake lines and alignments or offsets to lines using station andoffset methods. The software guides you directly to the line.Side Slope & Catch Point-Stake an earthwork operation that involves a tie to the currentground surface.Plane-Create and stake out a level plane, a sloping plane, or a 3-pointplane. The software guides you directly to points on the plane.Surface-Stake out from a design surface. The software guides youdirectly to points on the surface.This option is available only when the SCS900 road module isnot installed.Road Stake-roadway features, sideslopes, and catch points or anypoint on the surface.installed.Enter/Edit Stakeout Points-Add, edit, or delete any stakeout points that are in the currentdesign.
13 Settings menu Settings menu Units & Formats GPS Settings Internet & VRS SettingsInstrument Setup & AdjustmentStakeout SettingsData Output OptionsCOM Port Data Output OptionRadio Baud RateThe Settings menu contains all the SCS900 system settings that control the units ofmeasurement, how the software operates, and what tolerances the software will use fordifferent functions during operation.The settings provide control over Internet connectivity for VRS or remote base stationGPS operations.The settings also control what data is recorded during operation and then exportedwhen a work order is complete.Units & Formats-Specify the measurement units and the order of coordinates.GPS Settings –Specify GPS measurement and site calibration tolerances.Internet & VRS Settings-Configure your Internet connection for use with “intelligent”functions, a VRS system, or create a new connection withthe New Connection wizard.Instrument Setup & Adjustment-Specify horizontal, vertical, and angle setup tolerances and thetype of corrections to apply to the measured distanceStakeout Settings-Specify stakeout methods to be used, stake writinginformation, stakeout tolerances, and auto-aim controls for usewith a total station. Select map view options.Data Output Options –Specify .dxf file output options (surface measurements and/or3D faces). Specify whether or not raw data will be output witheach recordCOM Port Data Output Option-Enable the controller to output the instrument measurementdata through a COM port.Radio Baud Rate-Change the receiver to radio baud rate for third-party andTrimble PDL 450 radios.
14 Volume & COGO menu Volume & COGO menu Review & Edit Surface Review Design FeaturesCompute Distance & AreaCreate Stakeout PointsCreate/Edit Road DataThe Volume & COGO menu contains a number of calculation (area, distance, bearing,slope) and point generation functions ( free point, offset points, radius point) that canbe used to generate points for stakeout operation from CAD data in the currentlyloaded design.The menu provides access to the contour generation function, which you can use toreview a measured surface before you use the Compute Volume option, to determinestockpile or progress volumes. The menu also provides access to review and editfunctions for editing breaklines and deleting points or lines to resolve surfacemodelling problemsReview & Edit Surface-View or delete point and lines, add breaklines and boundaries,contour surface and calculate surface volumes (stockpiles) orperiodic progress volumes.Review Design Features-Calculate volumes based on the design data, and calculatedistances and areas.Compute Distance & Area-Compute areas, distances, and angles from measured orstakeout data.Create Stakeout Points-Create points by a variety of methods including free point,radius, and offset to a line. Free points can be created bytapping the screen or entering coordinates.Create/Edit Road Data-Enter a roadway and perform COGO functions based on a road.This option is available only when the SCS900 road module isinstalled.
15 System Setup menu System Setup menu (GPS) Set up Base Set up Rover Calibrate SiteRecheck System SetupEnter/Measure Control PointsSwitch to Total Station SetupThe System Setup menu contains the control and system setup functions for GPSFor GPS, use the menu to start the base station, start the rover receiver, and thencarry out the site calibration process.General functions include being able to enter and edit control point information,measure new control points for the project, and recheck the system setup on a controlpoint.The menu also provides the ability to switch between GPS and total station operations.Set up Base-Set up and start a Precision GPS base station.Set up Rover-Set up and start a GPS rover.Calibrate Site-Perform or resume a single-point, two-point, or multi-pointsite calibration.Recheck System Setup-Check an existing site calibration on a known control point.Enter/Measure Control Points-Edit and enter control point coordinates.Switch to Total Station Setup-Access the Total Station System Setup menu.
16 System Setup menu System Setup menu (TS) Connect Instrument Set up Total StationInstrument Functions MenuRecheck System SetupEnter/Measure Control PointsSwitch to GPS System SetupThe System Setup menu contains the control and system setup functions for GPS ortotal station operation:• For total stations, use the menu to connect the instrument and carry out stationestablishment to establish the position and orientation of the instrument. Themenu provides access to all total station control functions and calibrationprocedures.General functions include being able to enter and edit control point information,measure new control points for the project, and recheck the system setup on a controlpoint.The menu also provides the ability to switch between GPS and total station operationsConnect Instrument-Connect to the total station using a radio for roboticoperation or using Bluetooth® wireless technology forServo, Autolock, or Reflectorless operation.Set up Total Station Position –Set up the total station and establish its position andorientation on the site using the known point or arbitrarylocation (also known as free station or resection)methods.Instrument Functions Menu-Provides access to all total station specific functions andsettings in addition to calibration procedures for anglecollimation, tilt axis, and tracker collimation errors.Recheck System Setup-Check the current instrument setup on a known pointlocation.Enter/Measure Control Points-Edit and enter control point coordinates; measure newcontrol points.Switch to GPS System-Setup Access the GPS System Setup menu.
18 SCS900Note – Always set the distance units correctly before taking a measurement or associatinga design with the site. All files that relate to a single site must be stored and operated withthe same units. Once a measurement is taken, or a design is selected, you cannot changethe units.
19 Starting the GPS base station SCS900Starting the GPS base station
20 Positioning the GPS base station Located at a known or unknown pointPick a point from the control point listSet up on an unknown positionEnter its local coordinateEnter its lat/long/heightSet up radio onlyPositioning the GPS base stationPick a point from the control point listThis method enables you to pick a control point at which thebase station is to be located from the control point file. Thecontrol point can be selected from the map view or from thelist of control points. Place the base station at that specificlocation before initiating the base station setup. Typically,control points are established by the project surveyor. You canobtain the coordinates directly from the surveyor, or from theproject documents.Set up on an unknown positionThis is probably the most commonly selected method. The basestation is established at a convenient location for the project,where the antennas can be mounted high for optimumperformance and visibility of the sky. The best solution here isto establish a T-Bar at which the GPS receiver and antenna canrepeatedly be placed in the same location each day,eliminating possibilities for error. In this case,when you start the base station, the GPS receiver carries out a“Here” position using the GPS information to create a basestation location position. The GPS information determinedhere is an Autonomous position and contains a position errorthat will be computed and adjusted for as a part of the sitecalibration process.Enter its local coordinateEntering a local coordinate for the base station locationenables you to manually enter a point coordinate as opposedto getting it from the control point file. You can use thismethod for quick topo measurements where the site will becalibrated using a single-point calibration, or where the base stationwill be located on a control point, which has a known localcoordinate location. Enter the coordinate data as northing,easting, and elevation.Enter its lat/long/heightEnter the base station’s latitude, longitude, and height whenplacing the base station at a location at which those values areprecisely known, and one that is directly related to other sitepositions through the GPS site calibration.Set up radio onlyUse this method once a base station is established on a site andyou need to change the radio channel or network number forthe base station radio, for example, because the site isexperiencing interference from a third-party crew operatingnearby on the currently selected radio channel or networknumber.
21 Starting the GPS base station AutoBase®remembers how the previous setup was madereconnects the componentsselects the appropriate radio channelnetwork numberstarts to transmit GPS positionsWhen using the SPS781/SPS881 Smart GPS antenna or the SPS751/SPS851Modular GPS receivers, which use the AutoBase® technology, once a base station has beenestablished the first time, if nothing is changing between setups, you can simply set up thereceiver at the base station location and then switch it on. Using AutoBase technology, thereceiver reloads all appropriate data, makes all appropriate connections, and then starts to transmit corrections on the last used radio channel or network number. This eliminatesthe need to use a controller with the software to set up the base station each day.Note – If you want the SPS GPS (SPSx81 Smart GPS antennas, and the SPSx51 ModularGPS receivers) to operate in Autobase mode, you must name each base station with adifferent name, otherwise Autobase appears not to work.
22 Starting the GPS base station Before you start the base station, ensure that you do the following:Connect the controller to the receiver, if using a cable. Alternatively, you can make the connection using Bluetooth wireless technology from within the SCS900 software.Turn on the controller.Start the SCS900 software.Create a new work order on a new site if not previously created.Enter the control point coordinates for the project .1. Connect the controller to the receiver, if using a cable. Alternatively, you canmake the connection using Bluetooth wireless technology from within theSCS900 software.2. Turn on the controller.3. Start the SCS900 software4. Create a new work order on a new site if not previously created5. Enter the control point coordinates for the project
23 Setup Base To set up the base station System Setup Setup Base Select ConnectionWirelessCable
24 Connection Method Wireless Cable connect through Bluetooth wireless technologyCableconnect through a cable
25 Wireless Connection Scan for available Bluetooth devices If the receiver has previously been used as a base station on this site, then theSCS900 software first scans to see if the last used receiver is available through aBluetooth wireless connection. If found, the SCS900 software displays a messageasking if you want to connect to the last used receiver.The SCS900 software connects to that receiver and enables you to proceed with the base station setup:
26 Correction Method Transmitting RTK Corrections Via radio in the receiverVia Trimble/PacCrest radio using cableVia Trimble Bluetooth radioVia a third-party radioVia a cell phoneVia radio in the receiver –the SPSx51 receiver as a base station, it is likely that youwill select the option shown for both 450 MHz and 900MHz radio operationsVia Trimble/PacCrest radio using cable-any receiver with an external TRIMMARK 3, PDL 450, orHPB 450 radio for 450 MHz operationsNote – If you select this option, the software scans thedata controller serial ports to find a Trimble or PacCrestPDL radio. Ensure that the radio is connected to eitherPort 1 or Port 2 of the SPS GPS. To set the baud ratesettings for the PDL radio, from the main menu select(4)Settings. Click More and then select (2) Radio Baud RateVia Trimble Bluetooth radio-the SPSx81 GPS receiver as a base station for 900 MHzradio operations and you are using the external SNB900RadioVia a third-party radio-a third-party radio system excluding Pacific CrestVia a cell phone-a cell phone
27 Position the Base Located at a known or unknown point Non-available Options are grayed outPosition the baseOptions that are not available are grayed out. The above example shows:– Option (1) is not available because no control points exist in the currentsite.– Option (2) is not available because the base station has not been establishedon this site before.
28 Setup on unknown location Option only if site has not yet been calibratedOnce a site has been calibrated:Located at a known pointControl point in the calibration processEstablished using the measure control point functionYou can use this option only if the site has not yet been calibratedOnce a site has been calibrated, the base station must be located at a known point thatwas either used as a control point in the calibration process, or that has since beenestablished using the measure control point function
29 Setup on unknown location The software prompts you, noting that the base station should be set up in anopen location where the GPS antenna has a clear view of the sky (satellitevisibility)Because the base station is being set up at an unknown location, the positionthat is determined for the base station setup needs to be established as a controlpoint, so you need to enter a point name and code.In this case, the point has been named “a1” and the code has been named “stn”.This name and code is added to the control point file along with the measuredcoordinates on completion of the site calibration process. The base station’spoint name is also transmitted over the radio so that as the rover connects tothe base station, it can check that the incoming corrections are from the correctbase station receiver.
30 Pick a point from the control point list Method is most likely to be usedmoving the base station from one location on site to a new locationsite has been calibrated by a surveyorknown location is available only after you enter control point coordinatesThis method is most likely to be used when moving the base station from one locationon site to a new location. To do this, the site will typically have been calibrated and thereceiver has to be established at a known point.The method is also useful when the site has been calibrated by a surveyor, and you willuse the surveyor’s calibration instead of carrying out your own calibration. In this case,you must locate the base station receiver at one of the surveyor’s control points.Setting up the base station at a known location is available only after you enter controlpoint coordinates, which you can create either using the control point editor or by transferring a control point file from theoffice software to the controller.
31 Enter its local coordinate Known pointenter the base station locationThis is another known point (known station) base station location method. Instead ofpicking the point from the map view, you can enter the base station location as localcoordinates.
32 Enter its latitude, longitude, and height Another known pointpoint is a known pointlocal site coordinate is not knownhas been lostThis is another known point (known station) base station location method. Use thismethod where the point is a known point but the local site coordinate is not known orhas been lost.Instead of picking the point from the map view, you can enter the base station locationas WGS-84 latitude, longitude, and height. This information is known from the timethat the receiver was first set at this location, or from surveyor’s notes.This method enables you to enter the latitude, longitude, and height for the point andstill tie the base station into an existing site calibration.
33 Completing the GPS base station setup Antenna TypeGPS antenna from the list of antenna types.The following steps are the same for whichever option you selected to position thebase.In this example, an SPSx51 Modular GPS receiver is being used with an external GPSantenna, so you must select the appropriate GPS antenna from the list of antennatypes. Selecting the correct antenna type is very important, especially if the basestation’s configuration is changed at any time to use an alternate receiver or antennatype. This is because the antenna selection affects the height computed for the basestation location. In this example, the Zephyr Geodetic™ Model 2 antenna will beselected, which is most commonly used as the base station antenna with the SPSx51GPS receiver.
34 Base Antenna Height Antenna Height computed elevation for the base station positionwhere the antenna height is measuredEnter the antenna height so that the computed elevation for the base stationposition can be determined correctly.If using a T-Bar setup, where the antenna will be placed at the same location inboth position and elevation each day, the antenna height can be entered as 0.0 m(0.0 ft).Select to where the antenna height is measured. Typically, the height is enteredas a measurement to the bottom of the antenna mount. However, variousoptions are available from the Measuring list. Again, the method ofmeasurement is important, since the software uses known dimensions of eachsupported antenna to determine the correct elevation for the computed basestation location.
35 Radio Channel or Network GPS receiver usesChannelsFrequencyRadio networkDepending on which type of radio (450 MHz or 900MHz) is used, the GPSreceiver uses either channels and frequency (450 MHz) or the radio networknumber (900 MHz) to determine on which frequency or network to transmit theRTK corrections. For RTK operations to take place, the base station musttransmit, and the rover must receive data on the same channel or networknumber. SCS900 first queries the rover receiver to determine the current radiosettings. In the example shown, the receiver is using 900 MHz radios, so networknumbers are shown.Select the radio network number or channel on which the base station is totransmit.For 450 MHz radios, channel numbers are displayed rather than actualfrequencies such as MHz, so you need to have previously noted the actualfrequencies against the channel number in the radio so that all rovers can usethe same site frequency.If you are using a PDL 450MHz radio and you previously selected to connect tothat radio (2Select Connection option), the software displays a list of thechannels (such as 1, 2, 3) that the radio has available.
36 Checking Channel/ Network Skipno-one else is working within radio rangemake sure that no interferencesave timeAt this point the base station receiver is connected and tracking satellites, so thenumber of satellites being tracked is now shown at the bottom of the screen:Once set, the channel or network number selected is set to “receive” mode andscanned for a short period to make sure that the channel/network is clear beforesetting it to “transmit” mode and establishing the RTK correction stream. Thefollowing message appears:
37 Base Station information Set Up Base CompleteBase Station informationlogged to the work order report filehard copy recordre-establishedOnce the scan is completed, the receiver setup is complete, and the base stationinformation appears for you to check. The information is also logged to the workorder report file as a hard copy record of what was set up. This information canbe useful if the base station location has to be re-established for any reason.
38 Base Station WarningsGPS receiver is not receiving any satellite signalsLoose cable between the receiver and the antennacable between the receiver and the antenna is damagedswitched on after a long period of no useGPS antenna is obstructedIf the base station’s GPS receiver is not receiving any satellite signals from theGPS antenna, the following warning message appears:This message may be caused by one of the following:– The cable between the receiver and the antenna is not tightly connected atone or both ends.– The cable between the receiver and the antenna is damaged.– The receiver has just been switched on after a long period of no use, andneeds time to update its almanac and re-acquire satellites.– The GPS antenna is obstructed and has no clear view of the sky.
40 Types of site calibrations Three types of calibrationA single-point calibrationA two-point calibrationA multi-point calibrationIf points are suspectcontinues to warn yousurveyor for the project to check and validate the controlcheck your equipmentlevel bubble on your GPS rodthe rodtip of the rodA single-point calibrationUsed for short tasks or initial site measurements before control points havebeen established for the project.A single-point calibration involves measuring a single point location andassigning that location an arbitrary site coordinate value such as northing=5000,easting=2000, elevation=250. The calibration will orientate to GPS north. Thistechnique is often used for small site topographic measurements beforeconstruction, or for measuring stockpiles. If the collected data will be requiredlater for ongoing project operations, Trimble recommends that you mark outand measure a number of control points on the site. The control points can bemeasured later in the true coordinate system for the project, so the initialmeasurements can then be transformed onto the site coordinate system usingsoftware such as the Terramodel® Field Data Module. Data collected using asingle-point calibration does not suffer from degraded accuracy; it simply willnot tie in with the site coordinate system and design once that becomesavailable.A two-point calibration.Used where only two control points are available for calibration purposes. Thefirst point provides position; the second point provides orientation to a local sitecoordinate system, which may not be aligned with true north.A multi-point calibrationUsed on nearly all construction projects to match the GPS system to the localsite control and design coordinates for the project. Multiple control pointsspread around and across the jobsite are measured to provide an accuratetransformation computation that covers the entire project.A site calibration can be created in the office using a map projectionNote – If many points are suspect and the software continues to warn you that thecalibration is out of tolerance, Trimble recommends that you get the surveyor for theproject to check and validate the control before proceeding with operations. You may alsowant to check your equipment such as the level bubble on your GPS rod (to make sure thatit is correctly adjusted), the rod (to make sure that it is not bent), or the tip of the rod (tomake sure that it is not worn down and therefore giving height errors). You must keep thepole, pole bubble, and pole tip well adjusted and maintained to guarantee the best results.
41 This is the GPS calibration! Site CalibrationsThis is the GPS calibration!LocalNorth, East,ElevationWGS84Lat, Long,HeightIncludes datum transformation, map projection, horizontal & vertical adjustmentCan select from library or DC fileThe site calibration process involves measuring anumber of known control points in the local sitecoordinate system using a GPS rover, allowing theSCS900 software to create pairs of measuredlatitude, longitude, height and known northing,easting, and elevation values from which it canderive a transformation from a GPS position to asite coordinate system position.The site calibration is stored in a DC file thatremains associated with the site. The DC file iscompatible with the Trimble Survey Controller™software, so that the calibration data can be sharedif you are given a site calibration DC file fromsurveyors working on the project who use otherTrimble equipment. The SCS900 software can alsoexport the site calibration to a CompactFlash cardas a CFG file that can be used in the TrimbleSiteVision or GCS900 machine control systems.
42 Plane Coordinate Systems Mapping projections are used to represent positions on the curved surface of the earth as points on a flat surface or plane. Mapping projection surfaces used in surveying are designed to minimize the distortion that can occur when a curved surface is flattened.
43 Horizontal Adjustment RotationTranslationScaleAfter the WGS-84 positions have been transformed and projected as just discussed, there may still be some inconsistencies betweenthe grid coordinates produced from the GPS measurements and the grid coordinates that are accepted as true values for the respective points.To resolve these inconsistencies a horizontal adjustment can be applied to the GPS grid coordinates. The best adjustment of survey data employs the principle of least squares. The horizontal adjustment is an unweighted least squares best fit of the coordinates for the points determined by GPS to the coordinates of the points accepted as true.In the calibration, a grid coordinate obtained from GPS measurements is paired to a control grid coordinate for each calibration point. The result of the least squares best fit is a single set of parameters that describe how to make the GPS derived coordinates fit, as closely as possible, to the controlcoordinates.The parameters are:• Rotation of the GPS coordinates• Translation of the GPS coordinates• Scale factor for the GPS coordinates
44 Horizontal Adjustment = GPS observation= Control PointAfter the WGS-84 positions have been transformed and projected as just discussed, there may still be some inconsistencies betweenthe grid coordinates produced from the GPS measurements and the grid coordinates that are accepted as true values for the respective points.To resolve these inconsistencies a horizontal adjustment can be applied to the GPS grid coordinates. The best adjustment of survey data employs the principle of least squares. The horizontal adjustment is an unweighted least squares best fit of the coordinates for the points determined by GPS to the coordinates of the points accepted as true.In the calibration, a grid coordinate obtained from GPS measurements is paired to a control grid coordinate for each calibration point. The result of the least squares best fit is a single set of parameters that describe how to make the GPS derived coordinates fit, as closely as possible, to the controlcoordinates.The parameters are:• Rotation of the GPS coordinates• Translation of the GPS coordinates• Scale factor for the GPS coordinates
45 RotationAll of the horizontal points in the calibration are used to calculate a centroid (geographic center) about which a rotation of the GPS grid coordinates is applied. All of the observed GPS points in the project, even those not used in the calibration, will be rotated by the same angular amount. A minimum of two horizontal calibration point pairs are required to calculate a rotation parameter.
46 TranslationA translation moves all of the observed GPS coordinates in the same direction and by the same distance, so that they lie closer to the controlcoordinates. The translation parameter will be applied to all of the observed GPS (WGS-84) positions in the project. A translation parameter will be calculated with as few as one horizontal point pair used in the calibration.
47 ScaleA scale factor is determined using a ratio of the true distances, calculated between horizontal control coordinates, and the distances calculated between the GPS grid positions for the same points. This ratio of these two distances is the scale factor. The scale factor is applied to all of the GPS coordinates to obtain the best possible fit to the control coordinates. At least two point pairs must be used in the calibration to calculate a scale factor.
48 Horizontal Residuals Residual To perform the horizontal adjustment, at least three control points are needed. Each of these points must be observed with GPS as well as possess control coordinate values. Three points are required for the horizontal adjustment because it takes two points to derive the adjustment parameters and one additional point to provide a check on the fit obtained from those parameters. This check appears as residuals for each point in thecalibration.
49 Residuals Useful indicator Expected magnitude of a residual Quality of the calibrationControlMeasurementExpected magnitude of a residualquality of the control pointsfield proceduremeasurement methodssize of the site