Field Manual 3-34.331 TOPOGRAPHIC SURVEYING 16 January 2001

TOC Chap1 2 3 4 5 6 7 8 9 10 11 AppA AppB AppC AppD Gl Bib

Chapter 5

CONVENTIONAL SURVEY-DATA COLLECTION

Theodolites and transits are instruments designed to measure horizontal and vertical angles. As optical instruments progressed, the development of optics allowed the telescope to become shortened to the point that the optics could be rotated 360� horizontally. This act of turning the telescope has sped up work and permitted the qualitative review of sighting and instrument errors.

5-1. Surveys are usually performed to collect data that can be drawn to scale and plotted on a plan or map or to lay out dimensions shown on a design. Measurements for both types of surveys must be referenced to a common base for X, Y, and Z dimensions. The establishment of a base for horizontal and vertical measurements is known as a control survey. Conventional control surveys use two fundamental measurements angle determination and distance measurement.

ANGLE DETERMINATION

5-2. Horizontal angles are usually turned (or deflected) to the right or left. The three types of angle measurements are as follows:

• Interior angles. If angles in a closed figure are to be measured, the interior angles are normally read. When all interior angles have been recorded, the accuracy of the work can be determined by comparing the sum of the abstracted angles with the computed value for the closed loop (Figure 5-1).

Figure 5-1. Interior Angles on a Closed Traverse

• Deflection angles. In an open traverse (Figure 5-2), the deflection angles are measured from the prolongation of the backsight line to the foresight line. The angles are measured either to the left or to the right. The direction must be shown along with the numerical value.

Figure 5-2. Deflection Angles Shown on an Open Traverse

• Vertical angles. Vertical angles can be referenced to a horizontal or vertical line (Figure 5-3). Optical-micrometer theodolites measure vertical angles from the zenith (90� or 270� indicate a horizontal line). Zenith and nadir are terms describing points on a sphere. The zenith point is directly above the observer, and the nadir point is directly below the observer. The observer, the zenith, and the nadir are on the same vertical line.

Figure 5-3. Reference Directions for Vertical Angles (Horizontal, Zenith, and Nadir)

5-3. It is difficult to precisely set the angle values on the plates of an optical theodolite. Angles are determined by reading the initial and the final directions and then determining the angular difference between the two directions. Optical theodolites are generally very precise. The optical theodolite used by Army topographic surveyors (Figure 5-4) reads directly to 1" and by estimation to 0.1". Figure 5-4 shows that the micrometer was turned to read an even 10". This is done by moving the grid lines into coincidence, and then the micrometer scale reading (02�44") is added to the circle reading (94�10�) to give the resulting angle of 94�12�44". If several sightings are required for precision purposes, distribute the initial settings around the plate circle to minimize the effect of circle-graduation distortions. Table 5-1  illustrates the circle settings for 2 through 16 positions for a 1" theodolite.

Figure 5-4. Optical Theodolite

5-4. Because of the high-accuracy requirements for second- and third-order observations, constant precautions are necessary to counteract all error sources. The party chief should periodically inspect the performance of all observing parties. A good observer achieves the full potential of the instrument at all times. Signals and targets should be precisely bisected. Very little spread (three or fewer of the smallest increments marked on the micrometer) between the direct and reverse measurements should be consistently obtained. Proficiency can be attained only by a careful study of all factors affecting the accuracy of theodolite observations. Efforts should be made to eliminate all known error sources. Observation precautions are summarized as follows:

• Instrument check. Check the instruments and targets for stability. If an instrument is not stable, all other refinements are useless.
• Instrument adjustment. Pay careful attention to the parallax and the inclination of the horizontal circle plate. Errors introduced by the parallax and the inclination cannot be eliminated.
• Signal and target centering. Plumb signals and targets directly over the SCP. Carefully aim signals and targets towards the observing station.

5-5. Do not disturb the instrument while observing a position by releveling or striking the instrument or its support. Avoid any lateral thrust to a clamp, a tangent screw, or the electric switch. Other operational precautions for accurate observations are as follows:

• Repoint on the initial target after each circle setting.
• Check the plate level frequently.
• Protect the instrument from wind, sunshine, and precipitation.

5-6. When all other known precautions have been taken, one of the principal causes of error is horizontal refraction. Sometimes elevating the signal will reduce the effects of horizontal refraction, but often the only solution without altering the traverse is to reobserve the target under different atmospheric conditions.

5-7. Procedures for recording horizontal directions are the same for all orders of accuracy. Record horizontal directions on a DA Form 4253 (Figure 5-5) or any authorized single-sheet recording forms. When operating the AISI, use the appropriate recording media. In all cases, documentation should be completed in the field. Each time an SCP is occupied, the following information should be recorded:

Figure 5-5. Horizontal-Direction Recordings

• Instrument make, model, and serial number.
• Instrument operator's name.
• Recorder's name.
• Weather description.

• Temperature.
• General atmospheric condition.
• Wind.

• Designation of the occupied station.

• Full station name.
• Year established.
• Name of the agency on the disk.

5-8. The recording form should include the above information for each station observed. If an instrument, signal, or target is set eccentric to a station (not plumbed directly over the station mark), that item will be sketched on the recording form. The sketch should include the distance and the directions that the eccentric item is from the station. When intersection stations are observed, the exact part of the point observed must be recorded and shown on the sketch.

5-9. Numbers and letters should be approximately half the height between lines. The recording should be centered in the block and on the bottom line of the block. All figures must be neat and legible. There should be no erasures or obscuring of the original figures. Original numbers may be crossed out by using a single diagonal line through the numbers. The corrected numbers should be written above the original entry. The person making the correction will initial above and to the right of the original entry and within the block and will explain the reason for the correction in the remarks column. No position will be voided or rejected on any recording media, except in the case of bumping the instrument or stand, which causes the instrument to become unleveled. If the instrument is observed to be unleveled, make a note on the recording media in the remarks column stating that the instrument was not leveled and why. All recordings will be done with black ink. Directions will be entered in the remarks column (in degrees, minutes, and seconds).

5-10. The observer will check every computation on each page or sheet. The observer will verify the computation with a light, visible tick mark to the upper right of the computed numbers or will correct the numbers as described above. The observer will confirm that all computed numbers on the page have been checked by initialing at the bottom right corner of the page.

5-11. If a recording book is used, make an index (on the appropriate page) of the stations from which observations were made and recorded. An index is also required for all other recording media, indicating where to locate observations from any occupied SCP.

5-12. Second-order horizontal-observation specifications require that an abstract of horizontal directions be compiled for every station at which horizontal directions have been observed. DA Form 1916 (Figure 5-6) will be completed before leaving the SCP. Third-order horizontal observations require that the horizon closure, the corrected station angle, and the corrected explement angle be recorded before leaving the SCP. Readings will be entered opposite the proper circle position, as indicated in the field notes. The degrees and minutes for each direction are entered one time at the top of each column, and the seconds are entered for each circle position.

Figure 5-6. Abstracting Horizontal Directions

5-13. Record all observed positions on the DA Form 1916. If two or more observations have been made for the same target, list all the observations in the same box and determine the mean for that position.

5-14. Examine the listed positions. For any position that appears to vary greatly from the apparent mean of all the positions, check the computations in the field-recording book or other recording media. Be alert for a change in the minutes of the computed directions (angles) in the field data. Reject any positions that vary widely from the mean and then reobserve the positions. Enclose any values that are rejected by observation in parentheses and follow with "Ro."

5-15. Compute the mean of the observed positions. Round the mean value of a direction to the nearest 0.1" if a 1" instrument was used for observation. Reject all observations that differ from the mean by more than the rejection limit. Enclose any rejected observations in parentheses and follow with "R1." R1 indicates that the value was rejected using the first mean value. The rejection limit will be applied to each observation with the same amount of accuracy as when the mean was determined.

5-16. Reobserve any rejected positions and determine a new mean. Reapply the rejection limit. Enclose any positions still exceeding the rejection limit in parentheses and follow with "R2." R2 indicates that the value was rejected using the second mean value. Ensure that sufficient acceptable positions remain.

5-17. Do not reject any reading if it is within the rejection limits, unless it was rejected at the time of observation. If a value was rejected at the time of observation, check the field notes for the observer's reason for rejection. Once a value is rejected, it cannot be used again.

5-18. Do not use the mean of the readings if one of two or more readings on a position is outside the rejection limits. Use only the reading that is within the rejection limits. If two readings are outside the rejection limits (one is high, the other is low, and the mean is within the limits), the readings must be rejected. If there is a progressive change in the values of the positions of a direction or if the mean of the first half of the positions differs appreciably from the mean of the last half of the positions, attempt to observe another complete set of positions before leaving the SCP.

5-19. Recording vertical observations (zenith distances [ZDs]) is the same for all orders of accuracy. Vertical observations are recorded on DA Form 5817-R (Figure 5-7), an authorized single-sheet recording form, or appropriate media when operating the AISI. In all cases, complete documentation will be performed in the field. In addition to the recording requirements, record the following information:

• The HI above the station (recorded to the nearest 0.01 meter).
• A sketch of the observed target (that shows the point observed on the target) at the bottom of the object-observed column.
• The height of the observed target (HT) above the station being observed (recorded to the nearest 0.01 meter).
• A sketch showing any target's adjoining stations. This sketch will be drawn in the bottom of the remarks column. All possible points that may be observed will be measured and recorded to the nearest 0.01 meter.

Figure 5-7. Recording Observed ZDs

5-20. During vertical observations, the time of the first observation of the first position and the time of the last observation of the last position are recorded. The times are recorded to the nearest whole minute.

5-21. Vertical observations are abstracted onto DA Form 1943 (Figure 5-8) at the station site by the observing party. Targets or signals shown to other stations are sketched and dimensioned at the bottom of the form. If a target or signal is changed during the day, the time of the change and the new dimensions are also entered.

5-22. Vertical observations recorded as vertical angles are converted to ZDs before abstracting. The ZDs are abstracted, including the times of the observations. The abstracted ZDs are meaned and reduced to corrected ZDs by applying the reduction to line-joining stations. The following formula is used to determine the reduction in seconds:

where 
s = slope distance between stations (in kilometers)

5-23. This formula will also be applied to the vertical observations performed at the station at the other end of the observed line (reciprocal observations). The total length of the lines is multiplied by 0.46 (a constant based on the earth's curvature). Subtract 180� from the sum of the two corrected ZDs to determine the observed difference expressed as minutes of arc. If the two values differ by more than 1� of arc, perform a second set of reciprocal ZD observations. Differences exceeding 1� of arc are normally due to errors in observations or unusual refraction in the atmosphere (poor observing conditions).

DISTANCE MEASUREMENT

5-24. The distance between two points can be horizontal, slope, or vertical. A tape measure or an EDM device can measure horizontal and slope distances. In surveying, horizontal-distance measurements are always required. A distance measured on a slope can be trigonometrically converted to its horizontal equivalent by using the slope angle or vertical DE. Figure 5-9 illustrates a basic example of the geometry used to determine the horizontal distance of a measurement over uneven ground.

Figure 5-9. Geometry of an EDM (Basic Example)

5-25. Distances measured using an EDME are subject to the same errors as direction measuring equipment. The errors also include instrumental component errors. Instrumental errors are usually described as a number of millimeters plus a number of ppm. The accuracy of the infrared EDME AISI is �(5 millimeters + 5 ppm). The ppm accuracy factor can be thought of in terms of millimeters per kilometer, as there are 1 million millimeters in 1 kilometer. This means that 5 ppm equal 5 millimeters per kilometer. If the AISI is in the D-bar mode, the accuracy is �(2 millimeters + 3 ppm). Errors introduced by meteorological factors must be accounted for when measuring distances of 500 meters or more. Accurate ambient temperature and barometric pressure must be measured. An error of 1 degree Celsius (C) causes an error of 0.8 ppm for infrared distances. An error of 3 millimeters of mercury causes an error of 0.9 ppm in distance.

5-26. Although manufacturers provide instrument and prism constants, it is essential that instrument constants be verified under actual operating conditions, especially for precise surveys. The following factors must be considered:

• The use of a prism typically provides an indicated distance longer than the true value. Applying a negative correction will compensate for this effect. Each prism should have its own constant or correction determined individually, and a master file should be maintained.
• An instrument constant can be either positive or negative and may change due to the phase shifts in the circuitry. Therefore, a positive or a negative correction may be required.
• The algebraic sum of the instrument and the prism constants are referred to as the total constant. The correction for the total constant (equal in magnitude but opposite in sign) is referred to as the total-constants correction, from which the instrument or prism constant can be computed if one or the other is known.

UTM SCALE FACTOR

5-27. The scale factor (a computed factor) affects the measured distance. The scale factor for a particular UTM zone is solely dependent on the location of the survey in relation to its east-west distance from the UTM-zone CM. These zones are 6� wide and originate at 0� Greenwich meridian. North-south distances within the zone have no influence on the scale factor. The scale factor at the CM of UTM zones is 0.9996. The UTM scale factor toward the east and west from the CM increases to approximately 1.0004. Data-reduction procedures using the scale factor are necessary for precise surveys.

5-28. Distance measurements are not on a straight line. The earth's curvature and gravity affect the path traveled by the light beam. For a measured distance of 1 kilometer, the beam changes its path by nearly 7 centimeters. An approximate estimate of this effect is expressed by the following formula:

where 
VD = the vertical difference
0.0675 = the estimated effect on the path traveled by light
km = the distance in kilometers (for example, 0.9 or 1.2)

5-29. Distances measured by EDME will be recorded on authorized single-sheet recording forms. Figure 5-10 shows a completed DA Form 5819-R. If the AISI is used, the appropriate recording media is authorized.

Figure 5-10. Recording Electronically Measured Distances

ELECTRONIC TOTAL STATIONS

5-30. Electronic theodolites operate in a manner similar to optical instruments. Angle readings can be to 1" with precision to 0.5". Digital readouts eliminate the uncertainty associated with reading and interpolating scale and micrometer data. The electronic angle-measurement system eliminates the horizontal- and vertical-angle errors that normally occur in conventional theodolites. Measurements are based on reading an integrated signal over the surface of the electronic device that produces a mean angular value and completely eliminates the inaccuracies from eccentricity and circle graduation. These instruments also are equipped with a dual-axis compensator, which automatically corrects both horizontal and vertical angles for any deviation in the plumb line. An EDM device is added to the theodolite and allows for the simultaneous measurements of the angle and the distance. With the addition of a data collector, the total station interfaces directly with onboard microprocessors, external PCs, and software. The ability to perform all measurements and to record the data with a single device has revolutionized surveying. Army topographic surveyors use the AISI, which is addressed in detail in Section III.

5-31. A target is generally considered to be a nonilluminating signal. There are two general types of targets tripods and poles. Both target types may incorporate variations. Targets are constructed of wood or metal frameworks with cloth covers. For easy bisection, a target should be as narrow as possible without sacrificing distinctness. Triangular-shaped targets are the easiest to bisect. Square- and rectangular-shaped targets are the second easiest to bisect. Round targets are the hardest to bisect due to problems in pointing during repeated observations. Round targets should be avoided whenever possible. A target that subtends an angle of 4" to 6" of arc is easy to bisect. Since 1" of arc equals 0.5 centimeter at a l-kilometer distance, 6" of arch equals 3 centimeters at a 1-kilometer distance and 30 centimeters at a 10 kilometer distance. Under adverse lighting conditions, the target width will have to be increased. To make a target readily visible against both light and dark backgrounds, use material constructed of alternating bands of red and white or orange and yellow. Flags may be added or the background may be filled with blaze-orange cloth to contrast the target. All cloth used on the targets should be slashed after construction to minimize wind resistance and to avoid pilfering in areas where cloth may be valuable.

OPTICAL-THEODOLITE TARGET SET

5-32. The optical-theodolite target set is precise-survey equipment that is generally used for short traverse lines (about 4 kilometers or less). This target set (Figure 5-11) consists of a lower and an upper group. The lower group consists of a tribrach with a three-screw leveling head, a circular bubble, and an optical plumbing device. The upper group contains a plate with three triangles; a long, level vial; and a lighting attachment. The upper group is removable and is interchangeable with a theodolite.

Figure 5-11. Optical-Theodolite Target Set

AISI TARGET SET

5-33. The AISI target set is a combination precise-survey target and infrared signal reflector. It is used for angle and distance measurements. The target assembly (Figure 5-12) consists of a lower and an upper group. The lower group consists of a tribrach with a three-screw leveling head, a circular bubble, and an optical-plumbing device that can be illuminated. The upper group contains a long, level vial; a tiltable reflector/target for short-range measurements; and a long-range reflector/target assembly. The long-range assembly contains one to eight reflector prisms and three triangular-shaped target attachments. The reflector/targets are nonilluminating. The short-range tiltable reflector/target may also be attached to a range pole that has an attached circular bubble level.

Figure 5-12. AISI Target Assembly

5-34. The tripod target is the most stable, simplistic in construction, durable, and accurate. It ranges from a simple range pole to a tripod assembly that can be permanently embedded in concrete. All targets are susceptible to the effects of wind and precipitation. The tripod must be guyed or sand bagged and plumbed, and its legs should be securely set-in to prevent lateral movement. On uneven ground, one leg may have to be shortened or dug in to maintain a symmetrical appearance from all directions.

5-35. A range-pole target is used when the station does not require precise accuracy. The range pole is used to collect site-plan data quickly and in volume.

TARGET SETUP

5-36. Observers sometimes have a difficult and tedious task locating targets. Depending on the type of terrain and foliage in the area and in wooded areas where the targets are not profiled or silhouetted, they are very difficult to locate without direct sunlight shining on them. To expedite the locating of targets, it is sometimes necessary to illuminate the target area. Generally accepted procedures are as follows:

• Use of a handheld flashing mirror.
• Use of a strobe light or a portable light.
• Use of vehicle headlights.

5-37. Once a target area is located, it becomes a simple task to find the exact location of the target. The use of iridescent cloth on the target in place of regular signal cloth is recommended if the cloth can be interchanged.

5-38. In traverse operations where continual backsights and foresights are needed and where distances are not excessive, target sets can be used in a leapfrog technique. The actual distance a target can be seen depends on the background, the lighting, and the weather. Care must be taken when pointing a target at the observer so that the view is not distorted through the telescope. A disadvantage of a target set is that only one at a time may be set at a station. When setting a target, it must be plumbed exactly over a station. A target is said to be plumb when it is centered to within 2 millimeters of the point.

LIGHTED TARGET SETS

5-39. A target set is a precise-survey lighting device used for short traverse lines (about 4 kilometers or less). When a target set is used for night observations, it requires the attachment of an accessory lighting unit to the back of the target. The lighting unit consists of a metal hood with a light bulb mounted in the center. On the older target sets, the hood hangs on two small metal studs mounted at the top rear of the target. On the newer target sets, the hood slides down over the sides of the target from the rear.

TARGET AND TRIBRACH ADJUSTMENT

5-40. After the plate bubble has been centered, its position is checked by rotating the target (or instrument) through 180�. If the bubble does not remain centered, bring it halfway back using the foot screws to properly set it. For example, if the bubble position is off the center by four division marks, turn the foot screws to center the bubble until it is only off by two division marks. The bubble should remain in this position while the target is rotated. The target is now level and can be used, but the error should be removed by adjusting the bubble tube.

5-41. The bubble can now be adjusted by turning the capstan screws at the end of the bubble tube until the bubble is centered. Repeat the leveling procedure until the bubble remains in the center of the tube. Adjustments should be done in small increments, no more than half the error should be adjusted out at one time. At the end of the procedure, make sure the capstan screws are tightly secured.

5-42. Tribrachs use a circular level for rough and plate-fine leveling. After the plate bubble has been adjusted, the circular bubble can be adjusted (centered) by turning one or more of the adjustment screws located around the circular-bubble assembly.

5-43. The optical axis of the plummet is aligned with the vertical axis of the target (or instrument) if the crosshairs of the optical plummet stay superimposed on the center of the mark when the tribrach is revolved through 180�. If the crosshairs do not stay superimposed, the plummet can be adjusted using the following steps:

Step 1. Level the tribrach and put the crosshair over the mark and mark a point.

Step 2. Rotate the tribrach 120� and mark a second point.

Step 3. Rotate the tribrach a second 120� and mark a third point.

Step 4. Join the three points into a triangle.

Step 5.Draw a bisecting line from the center of the sides of the triangle to form the center of the triangle (Figure 5-13[A]).

Step 6. Adjust the optical plummet to the center of the triangle by loosening one side of the capstan screws and tightening the opposite screw (Figure 5-13[B]).

Step 7. Repeat the process to verify the adjustment.

Step 8. Ensure that all screws are snug after the adjustment is completed and that as little stress as possible is exerted on the capstan screws during the process.

Figure 5-13. Optical-Plummet Adjustment

SIGNALS

5-44. Signals are survey targets that are either illuminated by natural sunlight or are electrically lighted by using batteries. The observations for all second-order, Class I triangulation and traverse are usually done at night by using signal lights because of more stable atmospheric conditions, which allow for better pointings. Observations may be made during daylight hours if the work situation prevents nighttime observations. The most commonly used signal light has a 5-inch reflector. This signal light is used for lines of sight in excess of 8 kilometers. Do not use the 5-inch light on lines of sight shorter than 8 kilometers.A rule of thumb to follow for other light sizes is to add no more than 1-inch to the diameter of the light size for each mile observed.

5-45. The exact horizontal and vertical pointing of the light is very important. If the light is not pointed exactly toward the instrument, only a portion of the reflector will be observed. In some cases, this portion will not be plumbed over the station mark. The instrument operator must check the pointing before starting the observations by viewing the light through the telescope. During hazy weather and especially on long lines of sight, the view through the telescope may appear as a bright spot surrounded by a flare. The instrument operator should request that the light keeper adjust the light slightly in a horizontal and vertical arc while it is being viewed through the telescope until the best pointing can be determined. The best pointing is when the light is the brightest. The light is then stopped and locked into position. If the lights are stacked, the bottom light must be pointed first. It can be adjusted for brightness by adding or removing batteries. The light should never be improperly pointed to reduce its brilliance (this will create an eccentric light). The lighting attachment must be pointed directly at the observer to eliminate the appearance of uneven lighting of the target's triangles.

5-46. A light can be masked to reduce the size and brilliance of the beam by covering equal portions of the lens (both above and below and to the right and left of the center of the glass face). Opposite sides of the glass must be masked equally to eliminate eccentricity. This type of masking is very good for distances between 6 and 10 kilometers on normal nights. A sheet of orange scribe paper is required, but any other color will work almost as well. When using the orange paper as a masking material, the light will present an orange glow with a brilliant white cross for the observer to pointing on. At maximum ranges, the orange glow is practically invisible through the telescope, and at minimum ranges, the glow will help in identification of the light.

5-47. The light is focused by turning a screw at the rear of the bulb socket. By turning this screw, the position of the bulb is changed in relationship to the reflector. If the light is not properly focused, it will appear as a fuzzy ball in the telescope. The light may be focused by shining it on a flat surface about 50 meters away and adjusting the size of the beam until it is slightly larger than the light reflector. When no distant object is available, a field-expedient procedure is to hold one's hand about 6 inches in front of the light and adjust the light until a dark spot the size of a quarter appears in the center of the beam.

5-48. The type of light bulb and the amount of voltage being used will determine the brilliance of the light. The light is issued with two different bulbs: a standard 3.7- and a 6-volt bulb. The amount of voltage needed will vary depending on the lighting requirements. Various battery arrangements are shown in Figure 5-14. If dry-cell batteries are not available or are too weak, a field-expedient procedure is to connect two lights (with 6-volt bulbs) in a series and then connect them to a 12-volt wet-cell battery. Never apply more voltage to a bulb than its rated value.

Figure 5-14. Battery Wiring Diagram

5-49. When lights are needed from the same station to several observers, the signal lights are stacked, generally on a range-pole tripod (Figure 5-15). If lights are stacked over a station, they must be leveled and plumbed over that station mark. The lowest light must be leveled and plumbed first, then the other lights should be attached and individually leveled. Care must be taken not to knock the other lights out of plumb when attaching additional lights to the pole.

Figure 5-15. Stacking of 5-Inch Signal Lights

5-50. When observations are made from a small (low) instrument stand, it is sometimes impossible to plumb the lights directly over the station mark. If this occurs, it is acceptable to use the lights on a range. The lights must be aligned on a range to all stations with a theodolite. The standard theodolite tripod or range-pole tripod is used as a stand and should be from 4 to 30 meters from the station. Care must be taken to avoid introduction of eccentricities.

NOTE: A target set is used as a signal in the same way as when it is used as a target.

5-51. In the absence of a lighted target, a reflector may be used. By pointing a powerful, hand-held lantern flashlight at the reflector, a precise reflection will be returned. There are many other types of expedient lights or signals that can be used when standard equipment is not available or is inoperative. These include such things as the headlight of a vehicle, a masked lantern, a boxed lightbulb, or chemical illumination lights. The survey-party chief must use experience gained in the field and ingenuity to determine the proper expedient for a particular condition or problem.

5-52. The AISI is an electronic theodolite used to measure horizontal and vertical angles and distances. It represents these measurements on a display panel and can concurrently transfer them to a portable data-recording unit (DRU). The DRU can then transfer the data to an external microprocessor for printing, plotting, and further refinement by surveying software.

DESCRIPTION

5-53. The AISI has two modes a construction-survey mode with a range of 2 kilometers and a topographic-survey mode with a range of 7 kilometers. The AISI mounts on standard military tripods and consists of the following modular subassemblies:

• An electronic theodolite (a digital, automatic angle- and distance-reading/recording instrument with an electronic display/control panel).
• A DRU (an external memory device for storing data from the theodolite).

5-54. The AISI interfaces with microprocessors, printers, and plotters. It transfers digital data directly from its DRU (via a cable interface) to the microprocessor. The data is then refined by a fully integrated, 3D, ground-modeling, drafting-design system. The data can also be manually input to any CAD software program.

5-55. The AISI measures distances from 2 meters to 7 kilometers with a digital readout of 1 millimeter and is accurate to �2 millimeters + 3 ppm over the measured distance. The horizontal and vertical angles are measured to an accuracy of 1" of arc. The AISI has an electronic leveling device called a dual-axis compensator and adjusts for horizontal and vertical leveling with errors of 6" or less. The system has built-in communications with a range of 1 mile, an illuminated reticle for night operations, a 60-kilobyte memory capacity, and an alphanumeric keyboard and is powered by two dual-voltage, rechargeable, 12-volt nicad battery packs.

COMPONENTS

5-56. A detailed list of components for the AISI is described in TM 5-6675-332-10. The basic components for the AISI are shown in Figure 5-16. They are as follows:

• A transport case.
• A tribrach with an optical plummet, a battery pack, and a tribrach battery cable.

Figure 5-16. AISI System Components

• A lens and an eyepiece cover.
• A DRU and a DRU/AISI/battery cable.
• Internal and external nicad batteries.
• A battery charger and a charging converter.

LEVELING

5-57. The AISI uses a leveling device called a dual-axis compensator. It is an electronic device that senses the pull of gravity and uses two imaginary planes (one parallel to the instrument's face and the other perpendicular to that plane) at the base of the instrument for determining the level. The display simulates an actual bubble level, and foot screws are used to adjust the display bubble. The instrument then adjusts the horizontal and vertical axis to compensate for the instrument not being level. The working range of the compensator is 6�. That means that the instrument can be up to 6� off of level and still adjust the horizontal and vertical axis. The sensitivity of the display-bubble graduations is 6" in the fine-level mode and 20" in the coarse-level mode.

QUICK CHECK

5-58. A quick check is used to see if the AISI needs to be run through a collimation test. This procedure should be done at least once a day and also every time the instrument operator changes. Any time the quick check fails, the AISI should be calibrated. This check compares the sightings at a point target in the reverse and the direct modes. Pressing the angle-measure (A/M) key for each sighting will show the difference in the horizontal aim (dH) and the difference in the vertical aim (dV) on the screen. Failure is determined when the check of the dH and the dV is more than 5" for horizontal and more than 10" for vertical from the mean. The collimation test will produce a value to correct the angles (Figure 5-17). The procedures for the collimation test are described in TM 5-6675-332-10.

Figure 5-17. Quick-Check Example

DATA COLLECTION

5-59. The AISI has two ways of collecting data the coordinate method and the traverse method. In the coordinate method, all coordinates of points are collected in the field and all computations are conducted internally in the AISI. In the traverse method, all data is stored in the AISI in the form of raw angles and distances. This data is then downloaded into a survey software to compute coordinates. Surveyors determine which method to use. Table 5-2 shows the pros and cons for each method.