CVE 212 - Surveying Lab #1 MEASURING ANGLES & DISTANCES WITH A TOTAL STATION EQUIPMENT EDMI and Tripod Single prism mounted on a prism pole Field book Pencil 2 Walkie Talkies INTRODUCTION Recent developments of surveying equipment has been closely associated with advances in electronic technologies. Specific examples include electronic distance measuring instruments electronic data collectors, and GPS equipment. This lab focuses on introducing the student surveyor to the use of the electronic distance measuring instrument (EDMI). Prior to the use of the EDMI in surveying accurate distances were made by taping. Although taping appears to be a relatively simple procedure to the novice, precise taping is one of the most difficult and painstaking of all surveying duties. Current equipment technologies permit the measurements of distances to the nearest 0.001 of a foot, except for very short distances of less than 100 ft. The incorporation of electronic theodolites along with data collectors (electronic field books usually provided with an interface to a computer, printer, and/or plotting device) has resulted in the era of total station surveying. Slope distances are automatically determined through the use of on-board microcomputers that calculate and then display the horizontal and vertical component of the slope distance. The electronics included in a total station detects the vertical angle needed to calculate these distances. The electronics package also permits the instrument operator to determine the horizontal angle between two lines. The EDMI determines the distance between the instrument and a reflective prism located at a second point by measuring the phase shift of the signal transmitted to the prism and back to the instrument. The details regarding the theory that underpins this concept is presented in CVE 211. The student surveyor is directed to his/her class notes or the text utilized in CVE 211 for a complete discussion on this topic. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 1
PROCEDURE The objective of this lab focuses on familiarizing the student surveyor with the details of determining horizontal distances and horizontal angles using an electronic total station. To that end the procedures outlined in this section of the discussion are presented in three parts, i.e.,: positioning the total station instrument, measuring horizontal distances, and measuring the horizontal angles. Each student survey crew will re-survey the traverse that was taped in Lab #1. This includes determining distances between each bench mark in the traverse with the total station instrument. In addition the horizontal angle at each bench mark will be determined with the total station instrument. This information will be used to balance the traverse. To aid the discussion that follows the figure below depicts various parts of a Sokkia Set3B total station: Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 2
The numbered parts in the figure above are identified as follows: 1. Handle 2. Handle securing screw 3. Instrument height mark 4. Sub display 5. Main display 6. Lower clamp 7. Lower clamp cover 8. Tribrach clamp 9. Circular level 10. Circular level adjusting screws 11. Base plate 12. Leveling foot screw 13. Tribrach 14. Horizontal circle positioning ring 15. Keyboard 16. Objective lens 17. Tubular compass slot 18. Battery 19. Optical plummet focusing ring 20. Optical plummet eyepiece 21. Power switch 22. Horizontal clamp 23. Horizontal fine motion 24. Data output connector 25. External power source connector 26. Plate level 27. Plate level adjusting screw 28. Vertical clamp 29. Vertical fine motion screw 30. Telescope transmitting knob 31. Telescope eyepiece 32. Telescope reticle adjustment cover 33. Telescope focusing ring 34. Peep sight Throughout the remaining discussion the previous figure along with the list identifying various parts of the instrument will be referenced repeatedly. The student is advised to have this present during the lab. In addition to the figure identifying the various parts of the total station the following three part figure depicts the key board along with the main functions on the key board identified as well as the auxiliary (shift) functions identified. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 1
The student is advised to take heed of the following general precautions in utilizing the total station: Never place the total station on the ground. This will avoid damaging the tripod head and centering screw. Do not aim the telescope directly at the sun. The avoids damaging the LED in the instrument. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 4
Protect the total station with an umbrella against prolonged exposure to the sun, rain, snow and other elements of the weather. Never carry the total instrument on the tripod from one project to another. It is permissible to carry the instrument from one survey point to the next while the instrument is still on the tripod. Handle the instrument with care avoiding unnecessary shocks and vibrations. Always switch the power off before removing the battery. Remove the battery from the instrument prior to placing the instrument in the carrying case. Make sure the instrument is placed in the carrying case properly. Forcing the instrument into the carrying case will damage the instrument. Make sure the instrument and the protective lining of the carrying case are dry before closing the case and storing the machine. The case is hermetically sealed when it closes and if moisture is trapped inside the instrument can be easily damaged. A. Positioning the Total Station 1. Mounting the battery Turn the power switch (21) off before mounting the battery Close the battery release key cover Match the battery guide with the hole located in the recessed area for the battery Press the top of the battery until a click is heard 2. Set up the tripod and install the instrument on the tripod Make sure the legs of the tripod are spaced at approximately equal intervals and the leveling head is relatively flat Make sure the survey point is approximately in the center of the leveling head Place the instrument on the tripod head Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 5
Support the instrument with one hand and tighten the centering screw on the bottom of the instrument with the other hand. This will secure the instrument to the tripod 3. Center the instrument over the survey point Looking through the optical plummet (20) bring the survey point into focus by turning the eyepiece. If the survey point is not in your field of vision you must reposition the tripod and instrument. Once the survey point is in your field of view, adjust the leveling foot screws (12) in order to center the surveying point within the reticle of the eyepiece. 4. Level the instrument The total station is equipped with a bulls eye bubble. Observe the offcenter direction of the bubble in the bulls eye and shorten the nearest tripod leg, or extend the farthest tripod leg from the direction of the bubble and the center of the bulls eye. This procedure roughly levels the instrument. Loosen the horizontal clamp (22) so the instrument can be rotated such that the upper part of the instrument is positioned with the plate level (26) parallel to an imaginary line between two of the leveling screws. Keep in mind the adage the bubble follows the left thumb. If one hand turns faster than the other the screws bind, or the screws loosen (and the head rocks on two screws). Rotate the instrument through 90 and center the bubble in the bulls eye using the third leveling screw only. Rotate the instrument through 90 and check to see if the bubble remains in the bulls eye. If it does not repeat the previous two steps. When the instrument is level, slightly loosen the centering screw. Look through the optical plummet observe the survey point. Slide the instrument over the tripod head until the survey point is directly centered in the reticle. Tighten the centering screw. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 6
Check again to ensure the instrument is level by rotating the instrument and checking the plate level. If the instrument is not level, repeat the leveling steps given above. 5. Indexing the horizontal and vertical circles Turn on the power switch (21). The instrument name, model number, and software versions will appear for several seconds. An audio tone will sound and the instrument will perform a self diagnostic check. If the self diagnostic procedure concludes successfully the message Self check OK will be displayed for 2 seconds. After this message the remaining battery power is displayed for 3 seconds. If the battery is low on power a Battery is low message will appear. If this message is displayed turn the instrument off and inform the lab assistant. Once the instrument is powered up and functioning properly loosen the vertical clamp (28) and rotate the telescope through a 360 vertical angle. Indexing of the vertical circle occurs when the objective lens crosses the horizontal plane at which time an audio tone is sounded and the vertical zenith angle (ZA) is displayed. Next, loosen the horizontal clamp (22) and rotate the instrument through a 360 horizontal angle. Indexing occurs when the plate level (26) passes the 0 mark of the horizontal positioning ring. An audio tone sounds and the horizontal angle (HAR or HAL) is displayed. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 7
Each time the total station is powered up the vertical and horizontal indices must be determined. 6. Focusing the telescope Look through the telescope eyepiece (31) at a bright and featureless background. Do not point the telescope towards the sun. Turn the eyepiece either clockwise or counterclockwise until the reticle image goes out of focus. Bring the reticle back into sharp focus by slowly turning the eyepiece in one direction. The reticle is now focused relative to the student instrument operator conducting this procedure. B. Acquiring Horizontal Distances - Procedure 1. Sighting the prism Loosen the vertical (28) and horizontal (22) clamps and use the peep sight (34) on top of the instrument to locate the general direction of the prism. Tighten both clamps. Turn the focusing ring on the telescope (33) until the image of the prism sharpens in the field of view. Turn the vertical (29) and horizontal (23) fine motion screws to align the prism with the reticle. The last adjustment of each fine motion screw should be in the clockwise direction. 2. Select the distance measurement mode. Press the theodolite mode key sequence., i.e., the ent-shft key followed by the rcl key. The following options will be displayed. 1. Meas. mode 2. Prism const. 3. ppm Select the first option by pressing the menu-1 key. The other options will be set momentarily. The following options are displayed. 1. Fine 2. Coarse 3. Track Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 8
Select the first option by pressing the menu-1 key. The following display appears. 1. Single 2. Repeat Select the first option by pressing the menu-1 key. Return to the theodolite mode by pressing the ce-ca key. 3. Enter the prism constant Each reflecting prism has its own constant. Check the back of the prism for the constant that will be entered into the instrument at this point. Ask the instructor for help in determining the correct prism constant. Press the theodolite mode key sequence., i.e., the ent-shft key followed by the rcl key. The following options will be displayed. 1. Meas. mode 2. Prism const. 3. ppm Select the second option by pressing the prog-2 key. The previously stored prism constant is displayed and a p.c. image flashes to prompt for the current prism constant value. Enter the current prism constant by depressing the appropriate numerical keys. Press the ent-shft key to return the instrument to the preparation mode. The prism constant is displayed on the second line. Return to the theodolite mode by pressing the ce-ca key. 4. Enter the atmospheric correction Atmospheric correction is necessary for accuracy because the velocity of light in air is affected by temperature and atmospheric pressure. You should use the average atmospheric pressure and temperature to obtain the correction factor. To obtain this factor use the following table : Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 9
Press the theodolite mode key sequence., i.e., the ent-shft key followed by the rcl key. The following options will be displayed. 1. Meas. mode 2. Prism const. 3. ppm Select the third option by pressing the prog-3 key. The previously stored values of temperature and pressure are displayed and a T image flashes to prompt for the current temperature. Enter the current temperature by depressing the appropriate numerical keys. Note that the instrument is looking for a temperature in C. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 10
Press the ent-shft key to ready the instrument for the atmospheric pressure input. A P image flashes to prompt the for the current atmospheric pressure. Enter the current atmospheric pressure by depressing the appropriate numerical keys. Note that the instrument is looking for atmospheric pressure in millibar units. To convert atmospheric pressure from inches Hg to mbars, multiply inches Hg by 33.87. Press the ent-shft key to return the instrument to the preparation mode. The current temperature and atmospheric pressure are displayed in the second column. Return to the theodolite mode by pressing the ce-ca key. 5. The instrument will output distances in three formats, i.e., a. slope distance b. horizontal distance c. vertical distance Select the horizontal distance output mode. by depressing the triangle key with a bar under the horizontal leg. Note that the slope output mode is associated with the triangle key with a bar over the hypotenuse and the vertical output mode is associated with the triangle key with a bar next to the vertical leg. Once the horizontal output is chosen the instrument begins the signal acquisition process. After approximately 5 seconds the horizontal distance, zenith angle and horizontal angle are displayed. The angle information will be discussed momentarily. Press the ce-ca key to stop the acquisition process. Press the ent-shft key followed by 5 key to change the distance units from meters to feet. C. Acquiring Horizontal Angles - Procedure 1. Sighting the prism on the first bench mark Loosen the vertical (28) and horizontal (22) clamps and use the peep sight (34) on top of the instrument to locate the general direction of the prism. Tighten both clamps. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 11
Turn the focusing ring on the telescope (33) until the image of the prism sharpens in the field of view. Turn the vertical (29) and horizontal (23) fine motion screws to align the prism with the reticle. The last adjustment of each fine motion screw should be in the clockwise direction. 2. Press the ent-shft key followed by 0 key to reset the angle display value to 0. Note that the instrument defaults to measuring angles to the right unless the mode is changed. See the lab assistant for information regarding changing the angle mode. 3. Sighting the prism on the second bench mark Loosen the vertical (28) and horizontal (22) clamps and use the peep sight (34) on top of the instrument to locate the general direction of the prism. Tighten both clamps. Turn the focusing ring on the telescope (33) until the image of the prism sharpens in the field of view. Turn the vertical (29) and horizontal (23) fine motion screws to align the prism with the reticle. The last adjustment of each fine motion screw should be in the clockwise direction. 4. Read and record the angle currently on display. This is the angle between the first and second bench mark. D. Field Procedure 1. Position the EDMI over the initial station assigned to your student survey crew. Center and level and level the instrument Ensure that the telescope is at a convenient height for sighting. Position the tripod so that the legs do not interfere with establishing a line of sight with either the forward station or the back station from your position. 2. Position prism pole at the backsight. Communicate with pole person using walkie talkies to insure prism pole is plumb when taking a backsight. 3. Site on the prism. Attempt to focus EDMI in the prism (i.e., adjust optics such that the instrument can be seen in the mirror background of the prism). This can not always be accomplished with long backsights. Acquire the horizontal distance to the backsight. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 12
4. Position prism pole at the foresight. Communicate with pole person using walkie talkies to insure prism pole is plumb when taking a backsight. 5. Site on the prism. Attempt to focus EDMI in the prism (i.e., adjust optics such that the instrument can be seen in the mirror background of the prism). This can not always be accomplished with long backsights. Acquire the horizontal distance to the foresight. 6. Record horizontal angle between backsight and foresight. 7. Repeat steps 1 through 6 for every station in the traverse. 8. Balance the traverse using the compass rule. Calculations (including relative error) must be submitted to the instructor prior to conducting any further field labs. FIELD NOTES Use the following format for recording the angles and distances acquired in this lab. Note that only one repetition of the angles is required in this lab. In a later lab angles will be remeasured and accumulated several times on the horizontal circle of a theodolite. The student surveyor will also acquire the distances between stations using a steel tape, and stadia methods. So leave room for columns where this data can be inserted once these labs have been conducted. Balance the angles (include these calculations in your field book) and enter balanced angles as shown below. Include balanced angles and distances in the field sketch. Traverse Angles and Distances Single Adjusted EDM Taped Stadia Distance Distance Distance Inst. @ A BS G R to B 100 24' 50'' GA 428.34 428.1 428 AB 200.41 200.2 200 Oct 16, 1998 Greg S. Cold, Windy, 55 Denis Z. A G N B F Inst. @ B BS A R to C 167 25' 00'' BA 200.43 200.43 BC 287.1 287.1 C D E Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 13
In recording field notes, students should: Letter all notes carefully. The figures above should be used for form and style. Record field data in the field, not on scratch paper. One student can serve as the crew recorder and the student members in the crew can copy field data from the recorder s field book after the lab is completed. Designate each lab by title on separate pages in the field book. Each student must maintain a table of contents on the first page of his/her field book. The table of contents serves as a reference for the instructor and indicates page numbers for eac lab conducted. Indicate student survey party members, date, weather conditions, and equipment used. Use plenty of space. Notes should not be crowded. Draw neat sketches (always on the right hand page), roughly to scale, with important details exaggerated. NEVER ERASE ENTRIES IN THE FIELD BOOK. Corrections should be made by drawing a single line through the incorrect value and inserting the correct value above the erroneous value. Remember your field book can be subpoenaed as evidence in a boundary dispute. Erasure marks will disqualify the entire field book. Remember that other engineers will use the field notes. Therefore the data must be complete and unambiguous. For the taped distances between traverse stations sketch the entire traverse approximately to scale and show the length of all legs of the traverse, the interior angles and the direction of north. Also record weather conditions. Do not record the distances that will be used to make angle calculations on the same page in your field book that you record the distances between the traverse station. Sketch the near vicinity of the traverse station roughly to scale, showing just the lengths measured along each traverse course, the interior angle, and the direction of north. In addition, do not make your angle calculations on the same page in your field notes that you record the distances needed to make the angle calculations. On a separate page calculate the interior angle of the traverse in the field book. Prof. S.F. Duffy PhD, PE, F. ASCE Revised: 9/2/2006 Page 14