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ELECTRONIC THEODOLITES, ELECTRONIC TACHEOMETERS,

TOTAL STATIONS & DATA COLLECTORS

Electronic theodolites operate in a manner similar to that of optical theodolites or even vernier transits. Angle readouts are to 1 second, with accuracies from 0.5 to 10 seconds; digital readouts (LED or LCD) eliminate the guessing and interpolation of circle and micrometer settings associated with scale and micrometer theodolites. Electronic theodolites have zero-set buttons for quick instrument orientation after the backsight has been set; horizontal angles can be turned left or right, and repeat-angle averaging is available on some models. Some models also include horizontal and vertical collimation corrections, and vertical circle readings referenced to zenith, horizon, or percent slope format. The most significant characteristic of electronic theodolites is their ability to be interfaced electronically to data collectors and to computers, permitting a quick, error-free transfer of field data to the computer. Electronic tachometers (ETI) combine electronic theodolites with EDM instruments both of which are interfaced to a data collector. In this configuration it is called a total station. These electronic tachometers can read and record horizontal and vertical angles together with slope distances. The microprocessors in the ETI can perform a variety of mathematical operations (e.g., averaging multiple angle measurements; averaging multiple distance measurements; X, Y, Z coordinate determination; remote object elevations (heights of sighted features); distances between remote points; adjustments for atmospheric conditions; and so on. In addition, attribute data such as point numbers, point codes, and comments can be included with the recorded field measurements. The data collector is usually a hand-held device connected by cable to the tachometer, although some manufacturers have the data collector included as an integral component of the instrument. The Lietz Set 3C has an on-board data collector with operation controlled via a remote-control device. This configuration has two positive aspects: 1. There is no cable to become entangled 2. There is no need to touch the instrument, and perhaps disturb it, in order to control the measurement and collection commands. Some of the data collectors described here are obviously capable of doing much more than just collecting data. The capabilities vary a great deal from one manufacturer to another. Similarly, the computational capabilities of electronic theodolites themselves also vary widely. Some electronic theodolites simply show the horizontal and vertical angles together with the slope distance, whereas others also show the resultant horizontal and vertical distances. The Leitz SET 3 has the additional capability of being programmed (independent of the data collector) to determine remote object elevation and distances between remote points. Providing theodolites with greater computational capabilities means that the surveyor could then use a less sophisticated (less expensive) data collector. Some surveyors prefer the simpler

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equipment, wishing to perform data adjustments on the office computer prior to the computation of X, Y, Z coordinates. Future trends seem to be in the area of lower-cost electronic theodolites and EDMs interfaced to simple data collectors. Adjustments and coordinate computations can be accomplished on office computers. These simple electronic tachometers will be affordable for all surveyors. Early models of electronic theodolites used the absolute method for reading angles; that is, the instruments (e.g., Zeiss Elta 2) were essentially optical coincidence instruments with photoelectric sensors being used to scan and read the circles. Later ETI models (e.g., Wild T-2000, Lietz Set 3C, Geodimeter 460, Kern El, and Zeiss Elta 4) employ an incremental method of angle measurement. These instruments have glass circles that are graduated into unnumbered gratings. The number of gratings involved in a measurement is determined from whole-circle electronic scanning. Circle imperfections are thus compensated for, permitting higher precision with only one circle setting. The distance measurement is obtained using electro-optical range finders. Many ETIs have coaxial electronic and optical systems, thus permitting simultaneous electronic and optical pointing. The on-board microprocessor in the ETI monitors the instrument status (e.g., level or plumb orientation) and controls the angle and distance data acquisition and processing. In addition to computing horizontal distances and differences in elevation, most ETI microprocessors will also compute coordinates. ETIs that have automatic data collection capability for angle and distance measurement are called total stations. In addition to the fully automatic instruments described here, there are a wide variety of instruments that have some of the total station characteristics. That is, some instruments have automatic distance recording and others have automatic distance and vertical angle recording. In each case, the non-recorded data must be entered manually into the electronic keyboard. Most ETIs are designed so that data stored in the data collector can be automatically downloaded to the computer via an RS 232C interface with appropriate transfer software. The data can be adjusted by the computer (mainframe, mini or micro) and can then be printed out or graphically portrayed by an interfaced digital plotter. The chief attributes of an ETI system are the speed and ease of data collection and processing, and the elimination of many of the usual opportunities for mistakes and errors. The only disadvantage in the use of ETIs is the lack of hard-copy field notes that can be scanned and checked in the field. Although individual lines of data can be recalled in the field from the data collector, the overall sense of the survey must wait for the computer printout or digital plot. Recognizing this danger, ETI surveyors carefully design their survey implementation in order to minimize errors and mistakes (e.g., use of rigidly specific techniques and redundant measurements); and they design the computer system output so as to highlight possible discrepancies (e.g., "extra" cross sections, profiles, and plan views). Any apparent output inconsistencies are quickly investigated in the field; the computer graphics and printouts can in

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some cases be available within 24 hours of the completion of the fieldwork. One data collector (Leitz) can be directly connected to a dot matrix printer, permitting a quick analysis of the field data. ELECTRONIC TACHOMETER OPERATION Typical field surveys require the acquisition of horizontal angles, vertical angles, and slope distances from the instrument station to any other point; in addition, survey attribute data such as point numbers and point identification codes are also required. All these data can be quickly captured by the tachometer, or entered via the keyboard.

Figure 1 shows a sketch of a control traverse in an area requiring a topographic survey.

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Figure 2 Typical Data Collector Codes

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Figure 2 will be used to illustrate typical procedures employed when using electronic tachometers. Initial Data Entry 1. Temperature: (degrees F or C). 2. Pressure: in. Hg. 3. Prism constant (-0.03 m is typical for many instruments). 4. Degrees or gon (grad) selection. 5. Foot or meters selection. 6. Some instruments also provide for these additional entries: a. Sea-level correction. b. Curvature and refraction settings. c. Number of measurement (distance or angle) repetitions for each sighting. d. Choice of direct and reverse positions. e. Automatic point number increments. After the initial data have been entered, and the operation mode selected, the collector program will prompt the operator for all entries in sections B and C (see below). Instrument Station Identification Entries 1. Height of instrument. 2. Station identification number (e.g., #111, Figure 1). 3. Station identification code (see identification dictionary, Figure 2, for example, 02 (CM) concrete monument. 4. Coordinates of instrument station (northing, easting, elevation). 5. Coordinates of backsight station 114 (northing, easting, and elevation) or a reference azimuth to the backsight station. 6. Note: Some instruments do not permit entry of coordinates, relying instead on the computer program to prompt for these entries later.

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Data Collection Entries 1. Sight BS at station 114, zero horizontal circle; most tachometers have a zero-set button. 2. Enter code 20 (BS), Figure 2. 3. Measure and enter the height of the reflector (HR). 4. Press the appropriate measurement buttons: distance, horizontal angle, and vertical angle. Press "record" button after each measurement. Some instruments record the three measurements after pressing one button, in the "automatic" mode. 5. After the station measurements have been recorded, the collector will prompt for the station point number (e.g., #114) and the station identification code (e.g., "coordinate monument"-#08, Figure 2 dictionary). 6. If appropriate, as in traverse surveys, sight in the FS at station 112 (use operation code 30, Figure 2). Update parameters if necessary (e.g., HR, temperature, etc.). Press the measure buttons and record. Identify point number (112) and point code (e.g., "coordinate monument"-#08, Figure 2 dictionary). 7. While at station 111, any number of intermediate sights (IS) (use operation code 40, Figure 2) can now be taken to define topographic features being surveyed. The prism (reflector) is usually mounted on an adjustable-length prism pole with the height of the prism set to the height of the instrument (HI). The prism pole can be steadied with a brace pole to improve the accuracy for precise sightings. It should be emphasized that when working to high precession, as in traverse surveys, the prism should be tribrach-mounted on a tripod. 8. When all the topographic detail in the area of the occupied station (# 111) has been collected, the tachometer can be moved to the traverse station (e.g., #112), and the data collection can proceed in a manner similar to that already described (i.e. BS at station 111, FS at Station 113, plus all relevant IS readings). Data Transfer and Data Processing In the example shown in Figure 1, the collected data must now be downloaded to a computer; the ETI manufacturer normally supplies the download computer program, and the actual transfer is cabled through a RS-232 interface plug. Once the data are in the computer, the data must be sorted into a format that is compatible with the computer program, which is to process the data; this translation program is usually written or purchased separately by the surveyor. If the topographic data have been tied to a closed traverse, the traverse closure is calculated and then all adjusted values for northings, eastings, and elevations (Y, X, Z) are computed. Some ETIs have sophisticated data collectors (which are actually small computers) that can perform preliminary analysis, adjustments, and coordinate computations, whereas others require the computer program to perform these functions.

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Once the field data have been stored in coordinate files, the data required for plotting by digital plotters can be assembled, and the survey can be quickly plotted at any desired scale. Additionally, the survey can be plotted at an interactive graphics terminal for graphics editing, utilizing one of the many available CAD programs. SUMMARY OF TYPICAL ETI CHARACTERISTICS Parameter Input 1. Angle units: degree or gon 2. Distance units: feet or meters 3. Pressure units: in. Hg or mm Hg 4. Temperature units: F or C 5. Prism constant (usually -0.03 m) 6. Offset distance (used when the prism cannot be held at the center of the object) 7. Direct or reverse selection 8. Automatic point number increments 9. Height of instrument (HI) 10. Height of reflector (HR) 11. Point numbers and code numbers for occupied and sighted stations 12. Date and time settings for ETIs with on-board clocks Capabilities 1. Monitor: battery status, signal attenuation, horizontal and vertical axes status, and

collimation factors 2. Compute coordinates: northing, easting, and elevation 3. Traverse closure and adjustment 4. Topography reductions 5. Remote object elevation (i.e. object heights) 6. Distances between remote points

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7. Inversing 8. Resection 9. Horizontal and vertical collimation corrections 10. Vertical circle indexing 11. Records search and review 12. Programmable features (i.e. load external programs) 13. Transfer of data to the computer (down-loading) 14. Transfer of computer files to the data collector (up-loading) for layout purposes EDMs WITHOUT REFLECTORS Recently introduced EDMs utilize a timed-pulse signal, which permits the direct acquisition of distances by measuring the transit time of signals to and from the target. These EDMs can be used conventionally with prisms (range 8 to 10 km) and they can also be used without reflectors to determine distances to any topographic feature having a vertical component; the range for this technique is only 100 to 1500 m (Wild DIOR 3002S) depending on the light conditions. Accuracies of 5 to 10 mm are possible. These prismless EDMs are usually equipped with an optional target-marking laser, which permits the operator to confirm the specific feature that is being measured simply by observing the location of the visible laser spot. The laser beam width varies from 0.1 m at 50 m to 0.4 m at 200 m. Ideally, the target will have a light color and a smooth flat surface perpendicular to the measuring beam. This technology has large promise for the cross sectioning of excavated works and stockpiles, checking liquid levels, measuring to dangerous or non-touch surfaces (e.g., hot or fragile surfaces), displacement monitoring, and shore positioning for hydrographic surveys. When this EDM is interfaced to an electronic theodolite and data collector, the captured data can then be electronically transferred to a computer. Programs are available to compute areas, volumes, and so on, and to plot sections and profiles. AUTOMATIC DATA COLLECTORS Advances in computer technology in recent years have led to the development of sophisticated automatic data collections systems for taking field notes. These devices, sometimes called electronic field books, are about the size of a pocket calculator and produced by a number of different manufacturers. They are available with a variety of features and capabilities.

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The data collector is both a data recorder and a programmable computer. In using it for collecting data, field observations can be entered manually through the keyboard after reading them from a theodolite, and an electronic distance-measuring instrument (EDM), or other surveying instrument. However, its maximum utility occurs when it is directly wired (interfaced) with a surveying instrument having automatic readout capabilities such as a "total station". In this interfaced mode, angles and distances are transferred directly from the total station to the data collector's memory. For clarification of the notes, the operator inputs point identifiers and other descriptive information along with the data as they are automatically recorded. When a survey has been completed, or at day's end, the data stored in files within the collector can be automatically transferred to a larger computer for processing. When surveying at remote locations, data can be returned to the home office via telephone lines using devices called modems. Thus, office personnel can immediately begin using the data. Battery-operated portable disk drives and printers are also available so that periodically, for example, at the end of each day, field notes can be printed to obtain a readable "hardcopy" record and electronically stored to clear the data collector's memory for the next survey. Automatic data collectors are central components of modern computerized surveying systems. In these systems, data flows automatically from the field instrument, through the collector to the printer, computer, plotter, and other units in the systems. The major advantages of automatic data collection systems are (1) Mistakes in reading and manually recording measurements in the field are precluded, and (2) The time to process, display, and archive the field notes in the office is significantly reduced. As an example, the data for a survey can be corrected for systematic errors, and the misclosures computed, so verification that a survey meets closure requirements is made before the crew leaves a site. In using automatic data collectors, the usual preliminary information such as date, party, weather, time, and instrument number is entered manually into the file through the keyboard. For a given type of survey, the computer is programmed to follow a specific sequence of steps. The operator identifies the type of survey to be performed by means of a code and then follows the instructions that appear on the unit's screen. Prompts will call for input of information, which may include station names, descriptions, coordinates, and elevations, as well as distances and angles. Automatic data collectors are most useful when large quantities of information must be recorded, for example, in topographic surveys. Although automatic data collectors have many advantages, they also present some dangers and problems. There is the slight chance, for example that files could be accidentally erased through carelessness, or they could be lost due to malfunction or damage to the unit. Some difficulties are also created by the fact that sketches cannot be entered into the computer. This problem can be overcome, however, by supplementing the files with sketches made simultaneous with the measurements. Another unresolved question concerns the legal value of computer files, especially those containing boundary survey notes, for example. To aid in this regard, many data collection systems have a provision that protects files from any editing or tampering. In addition, hardcopy outputs can, and should, be obtained at the end of each day or job, and signed by the party chief. Automatic data collectors are available from a large number of manufacturers. They must be capable of transferring data with the various hard wares in modern surveying systems. Since

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equipment varies considerably, it is important when considering purchase of a data collector to be certain it fits the equipment owned or perhaps needed in the future. The use of total stations and data collectors is particularly beneficial in topographic Surveys. The method that works the best for topographic surveys is called the radiation method. In the radiation method, stations are occupied with a theodolite or transit and angles to desired contour points and features measured. Distances are found by EDM. After corners of buildings, bridges, and other details have been located, their lengths, widths, and projections are taped and sketched in the field book. The radiation procedure is especially efficient if a total-station instrument is used, and is further enhanced by an automatic data collector. Typically, the total station determines the geometry, and the operator has to input the features. Each brand of data collector has its own set of codes, but those shown below are typical. ENTRY EXPLANATION AC:SS (Activity: Sideshot/keyboard entry by operator) PN:3 (Point Number:3/keyboard entry by operator) PD:24IN MAPLE (Point Description:24 inch Maple/keyboard entry) HZ:16.3744 (Horizontal angle:16.3744 /by Total Station) VT:90.2550 (Vertical "Zenith" Angle: 90.2550 /by Total Station) DS:565.855 (Distance: 565.855 ft/by Total Station) AC:SS (Activity:Sideshot/Keyboard entry by operator) PN:4 (Point Number:4/keyboard entry by operator) PD:SAN MH (Point Description:Sanitary Manhole/keyboard) HZ:70.3524 (Horizontal angle:70.3524 /by Total Station) VT:91.1548 (Vertical "Zenith" Angle: 91.1548 /by Total Station) DS:436.472 (Distance:436.472 ft/by Total Station) AC:SS (Activity:Sideshot/keyboard entry by operator) PN:5 (Point Number:5/keyboard entry by operator) PD:SE COR BLDG (Point Description:Southeast corner Bldg/keyboard) HZ:225.1422 (Horizontal angle:225.1422 /by Total Station) VT:88.3035 (Vertical "Zenith" Angle: 88.3035 / by Total Station) DS:265.934 (Distance:265.934 ft/by Total Station) DIGITAL MAPPING GENERAL Survey drafting is a term that covers a broad spectrum of scale graphics and related computations. Generally, survey data are graphically displayed in the form of maps or plans. Maps are normally small scale, whereas plans are drawn to a much larger scale. The essential difference between maps and plans is characterized by their use. Maps portray, as in an inventory, the detail (e.g., topographic) for which they were designed. Maps can be of a general nature, such as the topographic maps compiled and published by the U.S. Geological Survey (scales normally ranging

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from 1:24,000 down to 1:1,000,000), or maps can be specific in nature showing only those data (e.g., cropland inventory) for which they were designed. Plans, on the other hand, not only show existing terrain conditions, but they also depict proposed alterations (i.e., designs) to the existing landscape. Most plans are drawn to a large scale, although comprehensive route design plans for state highways can be drawn to a small scale (e.g., 1:50,000) to give a bird's-eye view of a large study area. MAPS AND PLANS The topic of maps and plans is included to show how survey data, obtained from either ground or aerial surveys, can be graphically portrayed in scale drawings. The reproduction of maps involves photographing the finished inked or scribed map and preparing a printing plate from the negative. Lithographic offset printing is used to create the maps; multicolored maps require a separate plate for each color, although shading can be accomplished using screens. Scribing is a mapping technique in which the map details are directly cut on to drafting film that has a soft opaque coating. This scribed film takes the place of a photographic negative in the photolithography printing process. Scribing is preferred by many because of the sharp definition made possible by this "cutting" technique. Plans, on the other hand, are reproduced in an entirely different manner. The completed plan, in ink or pencil, can simply be run through a direct-contact negative printing machine (blueprint) or a direct- contact positive printing machine (white print). The white print machine, which is now in use in most drafting and design offices, utilizes paper sensitized with diazo compounds, which when exposed to light and ammonia vapor produce prints. The quality of white prints cannot be compared to map quality reproductions; however, the relatively inexpensive white prints are widely used in surveying and engineering offices where they are used as working plans, customer copies, and contract plans. Although reproduction techniques are vastly different for maps and plans, the basic plotting procedures are identical.

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Figure 3 Standard Paper Sizes

Figure 4 Typical Title Block

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PLOTTING The size of drafting paper required can be determined by knowing the scale to be used and the area or length of the survey. Standard paper sizes are shown in Figure 3. The title block is often a standard size and has a format similar to that shown in Figure 4. The block is usually (depending on the filing system) placed in the lower right corner of the plan. Revisions to the plan are usually referenced immediately above the title block, showing the date and a brief description of the revision. Many consulting firms and engineering departments attempt to limit the variety of their drawing sizes so that plan filing can be standardized. Vertical filing cabinets are designed such that title blocks in the upper right corner are more easily seen. SCALES AND PRECISION Maps and plans are drawn so that a distance on the map or plan conforms to a set distance on the ground. The ratio (called scale) between plan distance and ground distance is consistent throughout the plan. The scales can be stated as equivalencies, for example, 1 inch = 50 feet or 1 inch = 1000 feet, or the same scales can be stated as representative fractions 1: 600 (1":50 x 12") or 1:12,000 (1":1000 x 12"). When representative fractions are used, all units are valid; that is, 1:500 is the same scale for inches, feet, meters, and so on. Only representative fractions are used in the metric (SI) system.

Figure 5 Recommended Map Scales

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Figure 5 shows recommended map and plan scales and the replaced scales in the foot-inch system. Almost all surveying, required for the production of intermediate and small-scale maps, is done by aerial surveying methods. Maps are produced by photogrammetry. Even in municipal areas where services (roads, sewers, water) plans for subdivisions are drawn at 1:1000 and plans and profiles for municipal streets are drawn at 1:500, it is not uncommon to have the surveys flown and the maps produced by photogrammetry. For street surveys, the surveying manager will have a good idea as to the cost per kilometer or mile for various orders of urban density and will arrange for field or aerial surveys depending on which method is deemed cost - effective. Before a field survey is undertaken, a clear understanding of the reason for the survey is necessary so that appropriately precise techniques can be employed. If the survey is required to locate points that will later be shown on a small-scale map, the precision of the survey will be of a very low order. Generally, points are located in the field with a precision that will at least be compatible with the plotting precision possible at the designated plan (map) scale. For example, if we can assume that points can be plotted to the closest 1/50 inch (0.02) at a scale of 1:500, this represents a plotting capability to the closest ground distance of 10 inches (i.e., 0.02 x 500) whereas at a scale of 1:20,000 the plotting capability is (20,000 x 0.02) = 400 inches or 33.33 feet of ground distance. The latter example is rarely encountered since most surveys for maps at 1:20,000 are aerial surveys. In the former example, although plotting capabilities indicate that a point should be tied in to the closest 0.75 ft., in reality the point probably would be tied in to a higher level of precision (e.g., 0.1 ft.). In this regard, the following points should be considered: 1. Some detail can be precisely defined and located (e.g., building corners, subway tracks,

bridge beam seats). 2. Some detail cannot be precisely defined or located (e.g., stream banks, edges of a gravel

road, centerline of ditches, limits of a wooded area, rock outcrops). 3. Some detail can be located with only moderate precision, using normal techniques (e.g.,

large single trees, manholes, catch basins, curbs, sidewalks, and culverts). Usually, the detail that is fairly well defined is located with more precision than is required just for plotting. The reasons for this are as follows: 1. As in the preceding example, it takes little (if any) extra effort to locate detail to 0.1 ft. than

it would to locate it to 0.75 ft. 2. By using the same techniques to locate all detail, as if all detail were precisely defined, the

survey crew is able to develop uniform practices, which will reduce mistakes and increase efficiency

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3. Some location measurements taken in the field, and design parameters that may be based on those field measurements, are also shown on the plan as layout dimensions (i.e., levels of precision are required that greatly supersede the precision required simply for plotting).

4. Most natural features are themselves not precisely defined, so if a topographic survey is required in an area having only natural features (e.g., stream or watercourse surveys, site development surveys, large - scale mapping surveys), a relatively imprecise survey method (e.g., stadia) can be employed, although total stations are more likely to be used in the field.

All topographic surveys are tied into both horizontal and vertical (bench marks) control. The horizontal control for topographic surveys can be closed-loop traverses, traverses from a coordinate grid monument closed to another coordinate grid monument, route centerline, or some assumed baseline. The survey measurements used to establish the horizontal and vertical control are always taken more precisely than are the location ties. Surveyors are conscious of the need for accurate and well referenced survey control. If the control is inaccurate, the survey and resultant design will also be inaccurate; if the control is not well referenced, it will be costly (perhaps impossible) to precisely relocate the control in the field once it is lost. In addition to providing control for the original survey, the survey control must be used if additional survey work is required to supplement the original survey, and of course the survey control must be used for any construction layout resulting from designs based on the original survey. AUTOMATED MAPPING AND COMPUTER-AIDED DRAFTING Numerous computerized systems have been developed to draw maps automatically. The major advantage of these devices is greater speed in completing projects. Secondary benefits include reduction or elimination of errors, increased accuracy, and preparation of a consistently more uniform final product. Moreover, all data can be stored in a data bank with different numerical codes for the various kinds of features, and recalled later for plotting in total, or parts for special-purpose maps. As an example, a city engineering department might need only roads and utilities, whereas an assessor may want only the property boundaries mapped. Scale and contour interval can be varied readily, and either English or metric units specified. The required input to a computer for an automated mapping system includes control data, topographic detail information, map scale, and contour interval. Appropriate programs direct the computer to solve for the positions of points using the survey data and to plot contours and other features. With contour information stored in the computer, profiles along selected lines can be plotted automatically. By including grade lines and design templates, survey stakeout information and earthwork quantities are obtained for projects such as highways and canals. Interactive drafting (CAD) systems, which include an interfaced computer, CRT screen, and automated drafting machine, are extremely versatile. They enable operators to design and draw maps and diagrams in real time using the computer. The operator can examine the visual map display on a screen as it is being compiled, and then make any additions, deletions, or changes as needed. As examples, lines can be added, deleted, or their styles altered; placement of symbols and

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lettering modified; lettering sizes and styles varied; and the map checked for completeness and accuracy. When the operator is satisfied that the map meets all requirements and is the optimum design, the automatic plotter is actuated to draft the final product. With a CAD workstation, a small-scale version of an entire map or diagram can be displayed on one screen and an enlarged portion of it on the other where the operator performs the drafting and/or design. An operator controls the system by making entries on the keyboard, or by selecting instruction from a command board (menu) with a cursor. Sophisticated software drives this system, making it extremely versatile. CAD can also be performed using standard personal computers if they are equipped with appropriate software. Today, most plotting is done over a network.

Figure 6 Topographic Map

Figure 6 is a portion of a topographic map for an engineering design project made using a CAD system. The data for drawing the map were compiled and digitized using a stereo plotting system.

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Figure 7 CAD drawn Mortgage Survey

In Figure 7, a computerized mortgage plat, was also prepared using a CAD system. Many different automated drafting and CAD systems are available with varying individual capabilities. Books and brochures that provide their detailed descriptions can be obtained from the manufacturers. IMPACTS OF MODERN LAND INFORMATION SYSTEMS ON MAPPING Modern multipurpose Land Information Systems (LIS) Geographic Information Systems (GIS), and Automated Mapping and Facilities Management (AM/FM) systems all require enormous quantities of position related land data. From this information, maps and other special purpose graphic displays can be made and analyzed. A typical LIS, for example, may include attribute data such as political boundaries, land ownership, topography, land use, soil types, natural resources, transportation routes, utilities, and many others. From the stored information, a user can display a map of each attribute category (or layer) on a screen, or several layers of data can be merged to produce combination maps. This merging or overlaying concept greatly facilitates data analysis and aids significantly in management and decision-making. If printed maps of any selected layers or combinations are desired, they can be produced rapidly using automated drafting equipment.

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The position related land attribute data needed for LIS and GIS can be collected from a variety of sources and entered in the computer. These include field surveys, aerial photographs, and existing maps. Modern surveying instruments such as the total stations and photogrammetric stereo plotters can produce huge quantities of digital terrain data in X, Y, and Z coordinates form rapidly and economically. New devices called raster scanners are able to systematically scan existing maps and other printed documents, line by line, and convert the information to numerical form. The processes of collecting and digitizing the data to support LIS and GIS operations are expected to place a heavy workload on surveyors for many years to come. The widespread availability of personal computers, together with the development of LIS and GIS, has resulted in the production of new types of digital map products. The U.S. Geological Survey, for example, has begun distributing so called Digital Line Graphs (DLG), which are data banks of planimetric map information; and Digital Elevation Models (DEM), which are arrays of position related elevations. Since these data are already in a computer format, they can be directly integrated with other layers of data in the information systems. U.S. Geological Survey long-range plans contemplate the possibility of eventually filling all requests for maps with digital topographic data rather than hardcopy maps. The data would be instantaneously transmitted; users could view the maps on a screen and then print their own hardcopies as needed.

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APPENDIX I

Appendix I Typical Map Symbols

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Appendix II

Appendix II Typical Plan Symbols