Total station Surveying

Total station surveying principles and equipment setting up.

1. TOTAL STATION

2. CONTENTS ELECTRONIC DISTANCE MEASUREMENT PARTS OF A TOTAL STATION ACCESSORIES ADVANTAGES AND APPLICATIONS INTRODUCTION TO ASTRONOMICAL TERMS FIELD PROCEDURE FOR TOTAL STATION SURVEY

3. ELECTRONIC DISTANCE MEASUREMENT Method of measuring distance between points electronically by using electro magnetic waves (Infra red, Micro waves etc…) Microwave requires transmitters/receivers at both ends Infra red use a transmitter at one end and a reflecting prism at the other end (Most commonly used) EDM devices are typically mounted on top of a theodolite, but can directly mounted on to a tribrach For Eg . Total Station is a combination of theodolite with built in EDM and Microprocessor

4. WORKING PRINCIPLE EDM is very useful in measuring distances that are difficult to access and are long distances. It measures the time required by a wave to be sent to a target and reflect back

5. Measurement of distance Two Methods Pulsed laser system Phase shift Method (Most commonly used) Pulsed Laser System Make uses pulses derived from an infra red/ visible laser diode Distance is obtained by measuring transit time and velocity of pulsed electro magnetic signal in travelling between TS & target and back Velocity V of pulses gets determined Transit time t is measured using electronic signal processing technique Distance, D = 0.5 * V * t Large no. of pulses gets analyzed during measurements

6. PHASE SHIFT METHOD Uses continuous EM waves Measures length by indirectly determining the number of full and partial cycles of transmitted E M between the two ends of a line EDMI (Electronic Distance Measuring Instrument) consisting of an electro wave generator, an oscillator , a modulator, a transmitter, and a receiver etc.. Modulated EM Wave is transmitted to the target , Placed at the other end of the line. The target, acting as a reflector, reflects the light beam back to the receiver , where the incoming light is converted to an electrical signal. A phase comparison is made between the projected and reflected signals. Then the amount by which the transmitted and received signals are out of phase gets measured electronically and get registered in a meter by getting converted to an equivalent distance.

7. PHASE SHIFT METHOD If the received signal is out of phase by a measure of Dq , Then the equivalent distance, d is d = Dq * l/360 l : Wavelength of the E M wave The distance is calculated as D = *[ n l + ( ) l] n : integral no . of wave length, l in the double path ( see next figure)  

8. TOTAL STATION

9. TOTAL STATION A n electronic / Optical Instrument An electronic theodolite having optical telescope integrated with EDM (Electronic Distance Meter) and Microprocessor with memory unit and other accessories Accessories consists of Keyboard , Display , Power Supply , data collectors, field computers, memory card etc… Provides (By measuring or estimating)all parameters ( Distances&Angles ) & derived values (corrections & cordinates ) of surveying simultaneously Values of parameters can get displayed in viewing panel Precision may vary from 0.1” to 20”

10. TOTAL STATION TYPES Based on minimum circle reading accuracy : 0.1” to 20” (For eg : 1” total station, 2” total station, 5”, 15” , 20” etc..) Based on Control Manual Robotic : (Operator controls from distance via remote)

11. PARTS OF A TOTAL STATION

12. SCREEN AND KEYS

13. WORKING OF SALIENT PARTS Handle : To carry the Instrument physically Bluetooth antenna : To communicate via Bluetooth wireless technology External interface hatch : To connect to external devices Instrument height mark : To measure height of Instrument Luminance sensor : Adjusts the brightness of screen automatically Guide light : To carry out setting out measurement effectively Objective lens : Laser pointer function : To sight a target in dark location Vertical clamp screw : Vertical fine motion screw

14. Trigger key: To carry out operation indicated by the soft key in bold type on the screen Horizontal clamp screw: Horizontal fine motion screw: Tribrach clamp: clamp the upper part of the instrument with lower part Telescope eyepiece screw: Telescope focusing ring: Sighting collimator : To aim in the direction of measurement point Instrument centre mark

15. A Total Station primarily consist of an electronic theodolite, an EDM, Microprocessor and many other accessories Body of a theodolite is divided into two broad parts, upper part -The Alidade & lower part – The Tribrach Alidade includes standards, telescope,EDM , Circles (horizontal & vertical) and other elements for measuring angles and distance Tribrach contains foot screws, circular level, clamping devise and treads

16. TELESCOPE Objective lens : focus on the object to form image at the plane of reticle Eyepiece lens : focus on the plane of reticle Axis or line of sight : Line joining the objective lens and the eyepiece lens Parallax : If there is relative motion between Image formed & reticle, parallax is present which should be avoided Lock & tangent screws for revolutions & rotations AUTOFOCUS It makes the telescope focus automatically to target. After aiming the telescope to the target, autofocus button gets pressed

17. ANGLE MEASUREMENT SYSTEM For horizontal angle measurement, two glass circles within the alidade are mounted parallel one on the top of other , with a slight spacing between them . In a levelled TS (Total Station) horizontal angle circles should be in horizontal plane For vertical angle measurement, two more glass circles are mounted in parallel with slight spacing between them but aligned in a vertical plane automatically in a levelled TS

18. MICROPROCESSOR Controls , measures , computes , Reduces observations/ data by providing commands through keyboard . Some salient functions To make circles zeroed instantaneously To observe angles by method of reiteration in either direction To observe angles by method of repetition Averaging multiple distances and angle observations Reducing slope distances into horizontal & vertical distances Computation of elevation from vertical distance components Computation of coordinates from horizontal angle and horizontal distance components

19. AUTOMATIC COMPENSATOR To get TS precisely indexed with the direction of gravity Automatically align vertical circles having zero degree oriented precisely upward towards the zenith. PLUMMET Build into either alidade or tribrach Provides a line of sight that is directed downwards , collinear with the vertical axis after leveling For accurate centering Laser variety provides a beam of collimated light

20. OPTICAL GUIDANCE SYSTEM One or two above or below the telescope tube at the end of the objective lens. These are light emitting diodes and emit a visible light pattern which enables a detail pole to be set directly on the line of sight and at the correct distance without the need for hand signals from the total stations In some instruments , OGS is represented as Guide Light . It is composed of lights that is divided into Green and Red sections. A poleman can ascertain the present position by checking the Guide light color as follows LIGHT STATUS MEANING Increased flashing speed Move towards TS Decreased flashing speed Move away from TS Fast Flashing Target at the correct distance Red Move target left Green Move target right Red & Green Target at correct horizontal position

21. ACCESSORIES INTRODUCTION Apart from salient components, some accessories are required for working with TS . Some of the Accessories are present as integral part of the TS – Control Panel , Data Collector , Memory Etc… Some others totally independent – Reflectors These are the Major accessories CONTROL PANEL DATA COLLECTORS MEMORIES REFLECTORS SOFTWARE

22. ACCESSORIES - CONTROL PANEL Control panel of a total station consist of a keyboard & multiple line LCD ( liquid Crystal Display) The keyboard enables the user to select & implement different measurement modes, enable instrument parameters to be changed and allow special software functions to be accessed. Multifunction keys in the keyboard carry out specific tasks and some other keys activate& display menu systems which enable the TS to be used as computer Keyboard is also used to code data generated by the instrument for mapping. If a code is entered from the keyboard to define the feature being observed, the data can be processed much more rapidly when it is downloaded into and processed by an offline based computer plotter.

23. The keyboard and display can be detached from the instrument and interchanged with other total stations and with GPS receiver. This enables data to be shared between different instruments and systems using single interface Thus combination of keyboard and display unit not only controls the operations of total station but also stores measurements and data

24. KEYBOARD Keyboard contains different types of keys to provide different commands to its micro processor which subsequently gets works carried out by its different parts. It contains different alpha numeric keys , option selection keys, switching keys, Power key , lighting keys etc.. Salient Keys Power Key : To switch between ON & OFF Illuminator Key : For lighting the reticle/keys and to select screen backlight brightness . To turn laser- pointer/guide light ON /OFF Star Key : To jump from each mode screen to the screen of checking/changing the various settings directly ESC Key : To cancel the input data/to return to previous screen TAB Key : To shift to next item

25. B.S Key : Delete a character on the left S.P Key : Input a blank space FUNC Key : To toggle between observation mode screen pages ENT Key : Select/Accept input word/Value Numeric – Alpha Keys : To input numerals and alphabetic characters α key : Input Mode Key (To switch between numeric and alphabetic characters) SHIFT Key : To switch between lower case and uppercase characters Target Keys : To switch between target types (Reflector & Non Reflector) PRG Key : To switch between program mode and basic mode Luminance sensor/ Microphone key

26. ACCESSORIES - DATA COLLECTOR Automatically receives and stores field notes in computer compatible files Control of the measurement and storage operations is maintained through data collector’s keyboard Point identifiers and other descriptive information with measurements may be recorded Preliminary information required to be entered manually before the collection of measurements For a given type of survey, data collector is programmed to follow specific steps Stores information in either binary or ASCII format

27. Data storage and entry are carried out through a series of step by step instructions displayed by the data collector Enable operator to scroll through stored data, display for review and editing in real time Data collectors are developed instrument specific, however there are some which are flexible Data collectors are of two types , External and Internal

28. EXTERNAL DATA COLLECTOR Can be interfaced with various instruments Has Windows CE OS , thus can run variety of windows software programs Can do variety of calculations directly in the field Has Bluetooth technology to communicate with other instruments and WiFi capabilities for connecting to internet

29. INTERNAL DATA COLLECTOR Data collection system as internal components directly into the equipment Incorporates all features of external data collectors Use Windows CE OS Pen & Pad arrangement /Key board is used to point on menus and options to run software

30. ACCESSORIES –DATA COLLECTOR… ADVANTAGES Mistakes in reading and manually recording observations are precluded Time to process , display and archive the field notes in office reduced significantly Execute program in field and in real time Most useful when large quantities of information is involved DISADVANTAGES Field data may be erased due to carelessness or malfunction of instruments All information can not be entered/stored in digital form Varied data structures from different manufacturers Need to be compatible to the computer/software in which data need to be considered further.

31. ACCESSORIES - MEMORIES Total station makes use of internal memories or memory cards for processing and storing information Internal memory on board storage capacity of about 5000 to 10000 coded survey points Data can also be stored on memory cards which are plugged into Total Station All memory cards should satisfy PCMCIA standards Data may get exchanged to/from PC from/to through card reader

32. ACCESSORIES - REFLECTORS TS Use return or reflected signals for measurements. This is obtained by using a specific reflector TS reflectors consist of special reflecting prism constructed from glass cubes or blocks Return waves or pulses along a path exactly parallel to the incident path but within a range of angles of incidence of about 20 degree A wide range of reflecting prisms are available to suit short as well as long range measurements Single & Triple prism sets for fixing on tripod stand ,mini-prism for pole mounting or 360 degree prism for robotic TS are being used Reflecting prisms are associated with a prism constant (distance between effective centre of the prism and its plumbing point) of the order of -30 to -40 mm

33. ACCESSORIES - SOFTWARE Operating System generally used is Windows CE Field Software or the measurement software . Field softwares are manufacturer dependent Processing softwares : These are which is made use to arrive at the final product of the data collected. Eg : Carlson , AUTOCAD, etc…

34. ADVANTAGES OF TOTAL STATION Quick setting of the instrument on the tripod using laser plummet On-board area computation program to compute the area of the filed Local language support Full GIS creation Automation of old maps Greater accuracy in area computation Graphical view of plots and land for quick visualization Integration of data base The area computation at any user required scale

35. Once the field jobs are finished , the map of the area with dimensions is ready instantly after data transfer It reduces the time taken for the survey considerably and it also able to measure up to 3 to 5 km distances. Comparatively easy to work with High precision

36. APPLICATIONS OF TOTAL STATION To measure horizontal and vertical angles To obtain the horizontal distance, inclined distance and vertical distance between points. To get the three-dimensional co-ordinates i.e.[ x,y,z ] of a point in space. To find the length of a missing the line To find the elevation of the remote object . To find the distance to a remote object To locate the points at a predetermined distance along gridlines. Calculation of Area of a closed figure.

37. Total station is extensively used in Mine Survey, C adastral Survey, Engineering Survey, Large scale Survey, Road / rail/ canal Survey Some total stations also have a  GNSS (Global Navigation satellite System) interface  which combines the advantages of these two technologies (GNSS – line of sight not required between measured points; Total Station – high precision measurement especially in the vertical axis compared with GNSS) and reduce the consequences of each technology’s disadvantages (GNSS – poor accuracy in the vertical axis and lower accuracy without long occupation periods; Total Station – requires line of sight observations and must be set up over a known point or with line of sight to 2 or more points with known location).

38. DISADVANTAGES OF TOTAL STATION It may be difficult for the surveyor to look over and check the work while surveying. The instrument is costly. And for conducting surveys using Total station, Skilled personnel are required. For an over all check of the survey, It will be necessary to return to the office and prepare the drawings using appropriate software The instrument contains sensitive electronic assemblies which have to be well protected against dust and moisture

39. PRECAUTION TO BE TAKEN WHILE USING A TOTAL STATION Use both hands to hold the total station handle Set up the tripod as stable as possible Do not move or carry a tripod with the Total Station fixed on it , except for centering Store the battery pack with the battery discharged Do not over tighten any of the clamp screws Take maximum care when the tribrach is removed from the Total Station

40. FIELD PROCEDURE FOR TOTAL STATION SURVEY Leveling the Total Station Leveling the Total Station must be accomplished to sufficient accuracy otherwise the instrument will not report results Leveling the instrument takes 30 to 45 minutes – make sure you can see all targets from the instrument station before going through the process

41. STEP 1 : TRIPOD SETUP Tripod legs should be equally spaced Tripod head should be approximately level Head should be directly over survey point

42. STEP 2: MOUNT INSTRUMENT ON TRIPOD Place Instrument on Tripod Secure with centering screw while bracing the instrument with the other hand Insert battery in instrument before leveling

43. STEP 3: FOCUS ON SURVEY POINT Focus the optical plummet on the survey point

44. STEP 4: LEVELING THE INSTRUMENT Adjust the leveling foot screws to center the survey point in the optical plummet reticle Center the bubble in the circular level by adjusting the tripod legs

45. STEP 4: LEVELING... Loosen the horizontal clamp and turn instrument until plate level is parallel to 2 of the leveling foot screws Center the bubble using the leveling screws- the bubble moves toward the screw that is turned clockwise Rotate the instrument 90 degrees and level using the 3rd leveling screw

46. STEP 4: LEVELING… Observe the survey point in the optical plummet and center the point by loosening the centering screw and sliding the entire instrument After re-tightening the centering screw check to make sure the plate level bubble is level in several directions

47. STEP 5 : ELECTRONICALLY VERIFY LEVELING Turn on the instrument by pressing and holding the “on” button (you should hear an audible beep) The opening screen will be the “MEAS” screen. Select the [Tilt] function Adjust the foot level screws to exactly center the electronic “bubble” Rotate the instrument 90 degrees and repeat

48. STEP 6: ADJUST IMAGE & RETICLE FOCUS Release the horizontal & vertical clamps and point telescope to a featureless light background Adjust the reticle (i.e. cross-hair) focus adjustment until reticle image is sharply focused Point telescope to target and adjust the focus ring Until target is focused Move your head from side-to-side to test for image shift (i.e. parallax). Repeat the reticle focus step if parallax is significant NOTE : When the instrument operator changes the reticle focus may need to be adjusted

49. MEASURING THE HEIGHT OF AN OBJECT Level the instrument at a site where the target can be viewed through the telescope and the mirror target can be setup directly below the target After powering on the instrument select “REM” from “MEAS” > “Menu” Ht = h1 + h2 h2 = S (sin θz1) (cot θz2 ) – S (cos θz1) NOTE : Instrument height does not affect this calculation

50. MEASUREMENT OF TARGET HEIGHT Set the Target Height from “MEAS” > “Menu” > “Coordinate” > “Station Orientation” > “Station Coordinate” Set the target height to the measured height of the mirror target. Make sure you use the metric side of the tape measure if working with metric units. You do not have to fill out the other fields for a REM measurement, however, it is good practice to measure and enter the instrument height. After entering the TH and IH make sure you press “OK” (F4) to accept new values. Press “ESC” to return to the “MEAS” menu Select the “MEAS” > “Menu” > “REM”, sight the mirror target, press [OBS] to measure “S”, then [STOP] Sight the object above the target for height measurement Select [REM] after sighting the top of the height target, and then [STOP] to stop the calculations

51. REM SCREEN RESULTS To re-shoot the mirror target use the [OBS] on the REM screen. Note that after selecting REM the instrument continues to make calculations in case you need to adjust the vertical angle on the height target . Select “STOP” to terminate calculations on the REM command.

52. Trouble-Shooting the REM Measurement The only numerical input is the target height so make sure that is entered correctly. When TH is changed make sure you hit the “OK” function key. If the instrument is reset (zeroed) TH will be 0.0 so if you make a REM measurement with TH=0 the answer will be underestimated by the actual TH. A quick check can be made by using REM on the mirror target – the answer should be the TH.

53. CALIBRATING THE INSTRUMENT Calibration must be completed before coordinates can be obtained 3 possible calibrations: Backsight by angle: must know instrument coordinates and have a landmark/target at a known azimuth Backsight by coordinate: must know instrument coordinates and have mirror target set on a position of known coordinates Resection (triangulation): must have 3 or more mirror targets established at known 3D coordinates

54. 3D COORDINATES Coordinates may be absolute or relative depending on survey requirements Surveying the area of a mining site would require relative coordinates, therefore, the initial instrument X,Y,Z coordinates may be 5000, 5000, 100 Surveys that have to match a downloaded aerial photo from the USGS would have to match UTM NAD83 coordinates so the starting point would have to be determined by an accurate GPS receiver

55. Calibrate by Backsight by Angle Remember that when the instrument is powered on it has a random X,Y coordinate system: you must align the instrument with your working coordinate system. Level the instrument on the desired starting survey marker. Make sure that on the last leveling step the optical plummet is centered on the survey point Measure the target height and instrument height Select [COORD] from the MEAS menu Select “ Stn. Orientation” and then “ Stn. Coordinate” Edit the “N0”, “E0”, and “Z0” fields to appropriate values (i.e. northing, easting, elevation of instrument)

56. Backsight by Angle continued.. Enter the instrument and target height if necessary Select [OK] when done

57. Backsight by Angle continued … Select “ Backsight ” and then “Angle” from the menu Sight the landmark/target of known azimuth relative to instrument with telescope Select “Angle” from menu. Note that the menu displays the zenith angle (ZA) and current horizontal angle (HAR) and is waiting for you to enter the known angle with [EDIT] Note : if you enter an azimuth angle as “85.4514” this will be interpreted as 85 degrees, 45 minutes, 14 seconds IMPORTANT ! You must select [OK] to accept the angle. Never use <Esc> to leave this screen

58. Backsight by Angle Continued… NOTE : because the backsight by angle simply sets the instrument horizontal angle encoder to match your desired coordinate system the mirror target is never “shot” by the beam. If you can accurately sight on an object or landmark such as a building corner the mirror target is not needed. Make sure the instrument is “locked” and accurately sighted with telescope before entering the backsight angle . Because there is no internal statistical measure of how well the backsight angle has been set it is imperative to check the backsight independently : Known point: shoot the target at a position of known X,Y,Z such as a GPS point. The result should be within the resolution of the GPS. Known angle: shoot to a landmark at a known azimuth from the instrument location- the angle should be within the resolution of the instrument

59. Backsight by Coordinate Use this method when you have 2 known survey points with the instrument established on one and the mirror target on the other survey point From the “MEAS” menu select [COORD] and then “ Stn. Orientation”. Set the instrument coordinates with “ Stn. Coordinate” and then select [OK] and return to “ Backsight ” Select “ Coord ” and then enter the backsight target coordinates (NBS, EBS, ZBS) and select [OK] Sight in the target and inspect the “ Azmth ” (it should be reasonable for your coordinate system). Select [YES] to calibrate. If you don’t select [YES] the coordinate system is still random

60. Backsight by coordinate … Always check the calibration of the instrument by shooting the target used for the back sight. The resulting X,Y,Z should be within the several cm resolution typical for a TS instrument. It is a very good idea to shoot other benchmarks within range to make sure accuracy is within acceptable limits

61. RESECTION Resection uses 3 or more known target survey points to automatically determine the X,Y,Z coordinates of the instrument This has the significant advantage of not requiring the instrument to be leveled exactly on a survey point- any convenient location where you can sight the targets is OK The ideal geometry is displayed to the right

62. Resection continued… Prior to resection enter survey markers as known points through the “MEM” menu From the “MEAS” menu select “[MENU]” > [RESEC] The resection procedure requires that the known coordinates be defined first, and in the order that they will be shot In the top right screen the 1st point has been defined and the 2nd point is being entered. You can use [READ] to read in previously entered or measured points Press the “>” or “<“ arrow to move to next or previous point When all points are entered select [MEAS]

63. Resection continued… The [MEAS] screen (right) displays the point being shot – in this example the 1st point Choose [DIST] if you are shooting to a mirror target, [ANGLE] if not Select [YES] to accept measurement, [ NO] to re-shoot, [EDIT] to change target height The [CALC] option will be displayed when the standard deviation of northing and easting can be displayed

64. Resection continued… Press [CALC] or [YES] on last point to display the calculated instrument coordinates and the standard deviation of easting ( σE ) and northing ( σN ). Press [OK] to finish Resection, and then [YES] to set the backsight azimuth to the 1st shot point Press [RESULT] to display the residuals of each shot point- large deviations identify “bad” points If there are no problems press {Esc} to return to main resection screen The standard deviations are a measure of the accuracy. They should be in the range of several cm’s for most surveys

65. Resection Notes Resection initializes the X,Y,Z coordinates of the instrument. Save this as a point (ex. G1S02 for group 2, instrument station #2) since it represents a surveyed coordinate Once the instrument is calibrated the mirror targets can be taken down and used elsewhere The instrument height should be entered before resection is calculated You can only begin shooting resection point 1 from the resection point #3 or higher coordinate entry screen

66. Resection Notes Certain Geometries should be avoided: Targets and Instrument should not be arranged on a circle

67. Coordinate Measurement Used to determine XYZ coordinates of target point. Make sure the instrument height and target height are already set. Make sure backsight /resection have already “locked” the instrument into a mapping coordinate system From MEAS select Menu > Coord > Observation

68. Offset: Single Distance Single distance offset – used to measure points that cannot be “occupied” by the target. Examples : center of a large tree , center of a fountain center of a building

69. Offset: Single Distance Offset point can be right or left of the target, but must be the same distance from the instrument. Offset point can be in front or behind target, but must be on the same azimuth line. In any case the person/team holding the target must have a tape to measure the exact distance (to cm accuracy at least) of the offset. The instrument will request an observation to the target first, and then request the offset distance and where the target point is relative to the point of interest (left, right, front, back).

70. Offset: Single Distance Note the arrow that indicates that the target is to the left of the survey point by 2 meters.