H IG HWN i I..N.N.E.N. O.N DATA

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1 H IG HWN i I..N.N.E.N. O.N DATA Tran Tran VIRGINIA COUNCIL

2 Report No. 1. FHWA/VA-96-R34 Studies in Collecting Highway Inventory Data with Case Positioning System Global 9.Performing Organization Name and Address Transportation Research Council Virginia Edgemont Road 530 Charlottesville, VA Richmond, VA May 1996 Contract or Grant No. 11. No Project Type of Report and Period Covered 13. Report Final number of state departments of transportation, including Virginia Department of Transportation (VDOT), are A a geographic information system (GIS) to integrate data and to conduct more elaborate analyses which will improve ir developing capabilities. Research is currently being conducted at Virginia Transportation Research Council to determine decision-making of problems associated with implementation of this relatively new and evolving technology. collection and some accuracies of approximately 2 m were obtained. Time requirements and data collection problems were also described. se Point should ultimately aid VDOT in its GIS implementation process.!findings Key Words 17. GIS, HIGHWAY-RAILROAD CROSSING, GPS, Unclassified DOT F (8-72) Form Reproduction of completed page authorized restrictions. This document is available to public No NTIS, Springfield, VA through Report Documentation Page Technical Recipient's Catalog No Government Accession No. 5. Report Date 4. Title and Subtitle 6. Performing Organization Code 8. Performing Organization Report No. 7. Author(s) S. C. Brich and G. M. Fitch VTRC 96-R Work Unit No. (TRAIS) 12. Sponsoring Agency Name and Address Department of Transportation Virginia E. Broad Street Sponsoring Agency Code 15. Supplementary Notes In cooperation with U.S. Department of Transportation, Federal Highway Administration 16. Abstract of data sets required to drive GIS have been identified as two of largest expenses associated with GIS development This research looked at feasibility of using Global Positioning System (GPS) to collect some of locational implementation. and attribute data required to run VDOT's GIS. Data sets identified in VDOT's 10-Year GIS Strategic Plan were collected and transferred to ARC/INFO, a proprietary system, by way of hand-held, mapping-grade GPS receivers. Methods for collection and transfer of data sets were outlined. 18. Distribution Statement WETLAND DELINEATION, HIGHWAY DATA Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. Of Pages Price Unclassified 77

3 STUDIES IN COLLECTING HIGHWAY INVENTORY DATA CASE THE GLOBAL POSITIONING SYSTEM WITH C. Brich Stephen Research Scientist Transportation Michael Fitch G. Research Scientist Transportation Transportation Research Council Virginia Cooperative Organization Sponsored Jointly by (A Department of Transportation and Virginia University of Virginia) 1996 May 96-R34 VTRC FINAL REPORT opinions, findings, and conclusions expressed in this ( are those of authors and not necessarily those of report sponsoring agencies.) Cooperation with U.S. Department of Transportation In Highway Administration Federal Charlottesville, Virginia

4 Copyright 1996, Virginia Department of Transportation. ii

5 ARC/INFO GIS software package developed by Environmental Systems A Institute, Inc. Research of features in a geographic information system Characteristics or Coordinate GeOmetry (COGO) package. Every (GIS) features is geographic position. For example, a road has a survey or designated number, surface type, width, number of lanes, name and so on. Each attribute has a range of possible values, called a value chosen to describe a particular feature is called domain. attribute value. gravel, and concrete are a domain; and gravel is and, through differential correction, improves accuracy satellite GPS positions collected at unknown locations by a roving GPS of me, or a layer, such as soils, streams, roads, or land use. that describes features that will be located in field. Information description includes features names, data type classification This line, or area), attribute names, attribute types, and attribute (point, After being created on a PC, a data dictionary is values. to a datalogger and used when data are collected in downloaded field. definitions *se derived from following references: Trimble Navigation Limited. March Mapping were General Reference. Sunnyvale, Calif.; Environmental Systems Research Institutes, Inc Understanding Systems ARC/INFO Method. Redlands, Calif.; J. G. Lyon and J. McCarthy (eds.) Wetland and Environmental GIS: of GIS. New York: Lewis Publishers (CRC Press, Inc.); and E.D. Kaplan (ed.) Understanding GIS: Applications Norwood, Mass.: Artech House, Inc. DEFINITION OF TERMS* Attribute identifiable feature has attributes. One common attribute of all particular value for a feature, chosen from domain of an A For example, surface type is an attribute; bitumen, attribute. Attribute Value an attribute value. Base Station called a reference station. A receiver that is set up on a Also location specifically to collect data for differentially known correcting rover files. base station calculates error for each receiver. digital version of a map forming basic unit of vector data A in ARC/INFO. A coverage usually represents a single storage Coverage Data Dictionary Principles and Applications. iii

6 Positioning Global (GPS) System GeoExplorer TM GPS receiver. process of correcting GPS positions at an unknown location data collected simultaneously at a known location (base with post-processed differential GPS (DGPS), base station logs In measurements in a computer file so rover users can differentially correct ir data upon return to base station. interval or data frequency in making observations. Measurement example, if data are measured every 15 sec, loading data using For GPS consists of a constellation of 24 satellites (called from NAVigation Satellite Timing And Ranging) NAVSTAR, orbits earth once every 12 hr at an approximate height satellite km. system provides accurate, continuous, of three-dimensional position and velocity information to worldwide, with appropriate receiving equipment. GPS can provide users to an unlimited number of users since user receivers service passively (i.e., only receive). A GPS receiver calculates its operate by using known location of each of satellites from position it is receiving signals and time it takes for signal to which 4 different satellites are required to calculate position of from GPS receiver by solving for unknowns: latitude, longitude, set of ordered coordinates that represents shape of A features too narrow to be displayed as an area at geographic scale (e.g., contours, street centerlines, streams) or linear given with no area (e.g., state and county boundary lines). features A hand-held, lightweight data entry Also called a data recorder. Datalogger computer. datalogger used in this study was a Trimble Differential Correction process of differentially correcting one receiver's station). location relative to anor's can be done during post processing. Epoch 30-sec epochs means loading every or measurement. Feature A physical object or location of an event. Features can be eir (a tree or a traffic accident), lines (a road or a river), or points (a forest or a parking lot). polygons Each arranged in six orbital planes with 4 satellites per plane. travel from each of satellites to receiver. This information Signals determines distance from each satellite to receiver. and time. This position calculation process is known as altitude, trilateration. Line iv

7 similar to ghosts on a television screen that occurs Interference GPS signals arrive at an antenna having traversed different when pseudorange estimate and increases error. arise from reflections off structures near antenna. Multiple paths can positioning error resulting from interference between radio A that have traveled between transmitter and receiver waves single x,y coordinate that represents a geographic feature too A to be displayed as a line or an area, e.g., location of a tree small A multisided figure that represents an area on a map. A cellular data structure composed of rows and columns. Groups Raster cells represent features. value of each cell represents of necessarily square. typically consists of five principal components: antenna, receiver processor, input/output device, and a power supply. receiver, mobile GPS receiver collecting data during a field session. Any receiver's position can be computed relative to anor stationary GPS receiver. degradation of satellite signal by U.S. Department Artificial Defense (DOD). A DOD program to control accuracy of of measurements where user receives false pseudorange in error by a controlled amount. error in position pseudorange by selective availability (S/A) can be up to 100 m. caused GPS techniques can reduce se effects for local Differential Lock To track a satellite. Multipath paths. signal traversing longer path yields a larger Multipath Error by two different paths of different electrical lengths. Point or sign. Polygon value of feature. Each cell must be rectangular, but not Receiver device that processes signals transmitted from satellites A determine user's position, velocity, and time (PVT). A to Rover Post Processing See Differential Correction. Selective Availability applications.

8 computer operating system that controls flow of data, A of or programs, organization and management of application coordinate-based data structure commonly used to represent map A Each linear feature is represented as a list of ordered x, y features. to a raster data structure, which associated attributes with opposed grid ce 11). a UNIX files, and display of information. Vector coordinates. Attributes may be associated with a feature (as vi

9 number of state departments of transportation, including Virginia Department of A (VDOT), are developing a geographic information system (GIS) to integrate data Transportation conduct more elaborate analyses that will improve ir decision-making capabilities. and is currently being conducted at Virginia Transportation Research Council to Research some of problems associated with implementation of this relatively new and determine technology. collection and development of data sets required to drive GIS evolving looked at feasibility of using Global Positioning System (GPS) to collect some of research locational and attribute data required to run VDOT's GIS. sets identified in VDOT's 10-Year GIS Strategic Plan were collected and transferred Data ARC/INFO, a proprietary system, by way of hand-held, mapping-grade GPS receivers. to ABSTRACT have been identified as two of largest expenses associated with GIS implementation. This Methods for collection and transfer of data sets were outlined. Point accuracies of approximately 2 rn were obtained. Time requirements and data collection problems were also described. se findings should ultimately aid VDOT in its GIS implementation process. vii

10 STUDIES IN COLLECTING HIGHWAY INVENTORY DATA CASE THE GLOBAL POSITIONING SYSTEM WITH C. Brich Stephen Research Scientist Transportation Michael Fitch G. Research Scientist Transportation Michigan, Minnesota, and North Carolina, are developing GISs to integrate data Pennsylvania, conduct more elaborate analyses, which will improve decision-making capabilities of and Virginia Department of Transportation (VDOT) is also implementing a GIS to agencies. ir decision-making process. VDOT recently developed a 10-Year GIS Strategic Plan improve that will be used as a map" to acquire necessary tools and devise proper "road structure for a departmentwide GIS. 2 organizational consultant was contracted to develop a is acquisition of data. Hardware and software can be acquired more quickly than applications sets. Also, with few exceptions, hardware and software used for different applications data have features in common. data sets, however, will be at least somewhat dependent on will specific application being developed. refore, data acquisition is one of most important, and one of most expensive, steps in GIS implementation process. for cost of database development for a GIS are said to range from 50 to 80 Estimates of cost of GIS implementation. 3'4 Although se estimates include database design percent *Terms displayed in bold are defined in "Definition of Terms" on page iii. re are many FINAL REPORT INTRODUCTION A geographic information system (GIS) is an organized collection of computer hardware, geographic data, and personnel designed to provide for efficient capture, storage, software, manipulation, analysis, and display of all forms of geographically referenced update, information. A number of state departments of transportation, including Connecticut, GIS implementation for an agency as large and diverse as VDOT is extremely complex and time-consuming. A GIS Steering Committee was created in November 1988, and a private strategic plan to guide VDOT's GIS implementation. With recent completion of this plan, 10 priority applications were identified that will be pilot projects for future applications. A major component in implementation of se and maintenance, data acquisition comprises a large portion of this cost. method used to acquire data affects both cost of acquisition and quality of data set. ways to capture or transfer data in a digital format so y can be used by a GIS. Some of more common technologies used to collect data include Global Positioning System* (GPS),

11 digital photography, softcopy photogrammetry, high-resolution satellite imagery, high- video, document and image scanners, manual digitization of hard copy data, and real-time resolution systems and sensors. 5 through commercial vendors. digital photography, softcopy photogrammetry, high-resolution satellite imagery, Video, all image scanning capture data in a raster format. Unfortunately, although most high-end and vector format associates attribute data with a specific feature (i.e., point, line, or and All data that will be combined or analyzed need to be in a common format, which, polygon). does require that data already exist in some type of hard copy format. GPS data collection it based on recording current position of GPS receiver. Some of known benefits of is its ability to attach attribute information to feature while feature is being collected, and relatively low cost of hardware. GPS technology has advanced rapidly in collected, GIS Strategic Plan focuses primarily on computing requirements, VDOT's framework, data sharing, organization and staffing needs, strategic trends, and priority conceptual refore, re primary purpose of this project was to determine feasibility of and develop for using GPS to collect selected data sets that will be required to implement procedures implementation and reby help VDOT realize many benefits of using GIS sooner. Each technology has advantages and disadvantages that are somewhat dependent on data set being collected. In addition, particular data sets are now available software packages can handle raster data sets, y cannot normally be queried against GIS data sets. This is because raster format associates attribute values with a grid cell vector of its efficiency, is normally a vector format. Most data collected in a raster format must because converted into a vector format before being used by a GIS, a process that is extremely time- be consuming, imprecise, and expensive. Manual digitization and use of GPS result in vector-formatted data. Both methods very reliable and relatively accurate (although digitization depends on source being are Both are also labor intensive and time-consuming. Digitization is very versatile, but digitized). this technology are its ability to handle very large data sets, speed with which data can be last few years and is potentially one of best methods of data capture. applications. plan also identifies what a GIS can accomplish after information has been fully integrated into system. means of data collection, conversion, correlation, and integration are addressed only on a very general level, with few specifics given. is a need to determine which data collection methods are applicable for particular data sets that will eventually be required for VDOT's GIS. PURPOSE AND SCOPE applications identified in VDOT's GIS Strategic Plan. development of correct priority early in implementation process wiil reduce start-up time for GIS procedures

12 GeoExplorer TM GPS (mapping grade) receiver from Trimble Navigation, Ltd. was used A datalogger in this study (Figure 1). technology used in se receivers is basically as as that used in or receivers, and results should not vary significantly with use of same manufacturer's receiver. Although a limited number of applications and data types were anor for study, those chosen adequately represent types of data to be collected, ease of selected data, accuracy of data, processes used to correct data, and processes collecting computerized literature search was conducted to identify literature on using GPS for A collection and its transferability to a UNIX-based GIS. This literature, VDOT's GIS data Plan, and or documents pertaining to VDOT's implementation of GIS were Strategic reviewed. researchers supplemented literature by holding informal meetings with three resident engineers in central Virginia to gain insight into potential uses for a GIS at VDOT FIGURE 1. GEOEXPLORER TM GPS RECEIVER used to incorporate data into a UNIX-based ARC/INFO GIS. METHODS Literature Review Interviews

13 GIS Strategic Plan, prepared by Michael Baker and Associates, identified VDOT's GIS applications VDOT should focus on for development of priority departmentwide GIS a next 1 to 3 years. se applications are listed in Table 1. applications were over as having priority after consultant analyzed VDOT's business activities, operations, identified GIS operations so that a Department-wide solution can be determined, certain needs will current to be met, particularly for implementation of priority applications identified " have of three needs identified was "GIS Data Needs." That is, different types of data will be One to support priority applications. plan offered no clear suggestion on data required researchers selected three applications from list of priority applications and three data sets for which data collection could be carried out using GPS. representative 1 TABLE APPLICATIONS PRIORITY operations level. se interviews proved useful in developing list of data types for collection. Selection of Applications and Types of Data Sets To Be Collected and initiatives. consultant also stated that "in order for VDOT to expand and enhance needed to drive se applications or methods required to collect data. Safety Management System with National Environmental Policy Compliance (NEPA) and Water Quality Regulations (network Act level) Pavement Management System Bridge Management System Operations and Maintenance (network level) Fiscal Applications System Planning Applications Project Planning with NEPA and Water Quality Compliance (project level) Regulations Operations and Maintenance (project level) 10

14 three data sets selected were those for each GPS feature type: data collection process was monitored for time required to complete in-field collection using GPS, differential correction of information, and inputting of data to those managers assigning data collection teams to collect, download, and prepare information information for use in a GIS. development of an SMS on a GIS platform will require significant amounts of data and collection of new and more accurate pieces of information. To complement existing SMS, all public highway-railroad grade crossings in Albemarle County and City of were collected as point data. Each crossing location was collected, and its unique Charlottesville (DOT-AAR number) was recorded in GPS receiver's data dictionary to identify identifier crossing in office. VDOT's GIS Strategic Plan identified operations and maintenance as requiring a engineers was management of Adopt-a-Highway (AAH) program and resident of AAH segments. All of AAH segments in Greene County were collected as line location dictionary to identify segment in office. Polygon Data for Compliance with NEPA" Wetland Delineation with NEPA will require VDOT to collect and monitor a variety of Compliance location of wetlands created by VDOT for mitigation purposes potentially be a needed data set. GPS was used to collect boundary of a single created could site in Greensville County. Since only boundary of site was collected, data wetland selected were (1) Safety Management System (SMS), (2) Operations and applications and (3) Compliance with National Environmental Compliance Act (NEPA). Maintenance, point, line, and polygon. information into GIS. se steps and ir associated times will provide useful Point Data for SMS: Highway-Railroad Grade Crossings Line Data for Operations and Maintenance: Adopt-a-Highway Program "large,,2 quantity of items to be collected. One item continuously raised during interviews with data. names and route numbers of segments were recorded in receiver's data environmental data sets. were stored as a polygon. No attribute data were stored with location information.

15 Trimble GeoExplorer TM allows user to adjust parameters that affect way it and stores information. re are 22 user-defined rover settings. default settings collects feature. 6 logging: allows user to specify type of data being collected and how Feature positions are stored. point data were collected at 1-sec intervals, which often default setting. line features were also collected using 1-sec intervals even is 5-sec intervals is default. This setting was chosen to produce more though primarily because of alignment of roadway segments (sharp turns information, an abundance of curves) encountered, canopy cover, and mountainous and mask: sets minimum elevation above horizon for a satellite to be Elevation in position calculation. rover mask was set at 15, default. used strength from a satellite before signal is recorded. default value was used. type of material post is constructed of (wood, metal, etc.) can be input as conducted, data in data dictionary. Additional attribute values that user may want to build attribute into data dictionary for a This structure can be built in office so that user it was installed. data dictionary is capable of handling user-defined menu values, date attribute values, date attribute values, character attribute values, and time attribute numeric GPS Parameters Receiver Settings for this particular receiver were used in all but one instance. following values were used for most important settings: environment of most of secondary roads encountered. Signal-to-noise ratio (SNR) mask: allows user to specify minimum signal Position dilution ofprecision (PDOP) mask: sets maximum error allowance of recorded satellite positions. default value was used. Data Dictionary A data dictionary was developed for point and line features investigated. A data dictionary is no more than a user's pre-built structure to input attribute values for a particular Most GPS receivers that allow for storage of position data also allow for input of attribute data by way of a data dictionary. For example, when a stop sign inventory is stop sign inventory include type of sheeting used, size of sign, and date sign was installed. can simply input wher sign is supported by wood or metal, its type of sheeting, and values. text string for character attribute values may contain alpha and/or numeric characters.

16 data dictionary developed for highway-railroad grade crossing section one was accepted alphanumeric values. This is because primary goal of researchers that to was location of crossing and its DOT-AAR number. researchers developed enter to hold 6 numbers and 1 alphabetic character. This allowed m to enter attribute dictionary developed to have user enter two attributes for each feature" This dictionary was (1) name of group dictionary to hold name of AAH segment using character attribute developed capable of handling up to 12 characters and route number using numeric attribute values supplement feature data collection activities and address issues surrounding To of data, researchers conducted three sets of experiments. first experiment accuracy determining accuracy of point data using a known Geodetic Control Point High involved Reference Network (HARN) monument. This HARN monument, number AIG 1, was Accuracy of highway-railroad grade crossings. researchers recorded HARN site 10 collection in 10 different files. times second experiment used same HARN monument to determine accuracy of features. researchers developed an equilateral triangle with HARN location line point using GPS. line segment was recorded 10 times in 10 different files. opened, approximately 120 points were collected at each corner of triangle and file was n closed. This procedure was carried out 5 times, resulting in 5 files representing was number) for crossing while receiver was recording points locating (DOT-AAR crossing. A data dictionary was also created for AAH line feature. responsible for roadway segment and (2) route number for segment. researchers value to 4 places. Determination of Accuracy by National Geodetic Survey and is located in norrn Albemarle County. surveyed coordinates for this location are known and documented. To determine accuracy of exact receiver, a receiver was placed directly over monument and allowed to collect and store GPS for a minimum of 120 points. This method replicates procedures used in signals representing one corner of triangle and each leg of triangle being rn (150 ft) in length (Figure 2). side of triangle opposite HARN was collected using GPS receiver. This segment was used to determine segment's length and distance from known third experiment used same equilateral triangle (Figure 2). After GPS file same polygon area. files were n post processed and grouped using PC software package provided with receiver. points making up each file were n connected to form polygons. area calculations for each polygon, as well as ir respective location, were 5 compared. n

17 O = 60 popularity of GIS as a management tool has grown nationally, research has been As to determine appropriate methods to collect data that drive se systems. By far, initiated collection mechanism evaluated technology in three areas: initial data collection and constant updating of ever- accuracy, cost, and reliability or HARN L AIGI L = m (150 ft) FIGURE 2. HARN LOCATION AND EXPERIMENTAL TRIANGLE RESULTS Literature Review most expensive part of any GIS is evolving data sets. Most of very limited research done with respect to GPS as a data ease of use.

18 m, depending on a number of variables. Research conducted by Hyman et al. 7 for Arizona 10 of Transportation found that uncorrected data (not undergoing differential Department correction) had errors of nearly 100 m. accuracy of 16 rn needed for ir sign management system, y expanded ir study to location differential GPS (DGPS). With DGPS, errors between 2 and 5 rn were obtained. 7 Hook include al. found in ir use of GPS for collection of wetland boundaries that overall accuracies et on order of 5 m. Similar work by McGarigle 9 had accuracies ranging from 2 to 5 m, were addition to differential correction, or important variable determining In of GPS-collected data is number of epochs or signals recorded for a particular point. accuracy 10 and 60 epochs still result in errors of less than 5 m. 8'1 '11 research on feasibility of GPS to collect data for GIS did not consider cost of Most acquisition beyond simply factoring in purchase price of receiver. This price ranged data $4,0007 to $15,000. Poling et al. did compare staff hours associated with collecting from inventory data with GPS and staff hours associated with manual measuring with a sign researchers found that although data collection with GPS took more time in field (4 min feature as compared to 2.6 min per feature for manual measurement), it required less time to per se are careful implementation to ensure that costs of acquiring equipment do not exceed requires benefits that will be realized. Finding additional applications for data and its manipulation will ensure that benefits do outweigh costs of equipment. 7 Reliability/Ease of Use or criteria were used in limited research designed to determine ease of Several of GPS for GIS data collection. Hyman et al. wanted to determine (1) if technicians or field use Accuracy Most GPS vendors indicate that data collected with receivers is accurate to within 2 to After determining that se data did not meet depending on receiver's distance from base station used to post process data. values for work of both Hook et al. and McGarigle included differentially correcting GPS-collected data. manufacturers recommend that between 120 and 180 epochs be recorded and n averaged Most determine location of a single feature. Several studies, however, have found that between to Costs measuring wheel. Both types of data were n taken back to office for transfer into a GIS. post process and import into GIS (0.6 versus 2.9 min). In research conducted using DGPS, researchers included price of receivers used as base stations. more expensive than receivers used for field data collection and are not necessary, generally public base stations are made available. Hyman et al. warned that use of GPS assuming

19 could use GPS technology since y are typically responsible for most data personnel and (2) how much training would be required for se individuals to ensure accurate collection, collection of data, and that were common in most of literature, were loss of lock affected satellites because of overhead obstructions and interruptions in signal reception because of on affected by this, data should be recollected. 2 When signals are interrupted or is normally caused by heavy tree canopy. Some studies have found that this causes obstructions significant problem, whereas ors have found that this is not a significant problem a on density of canopy and speed at which receiver is moving. 8' Tall depending definitely limit signal reception and timing, thus severely affecting data collection and buildings accuracy. 11 receiver was over center of grade crossing with respect to both roadway and railroad placed center of crossing was defined to be where centerline of track (for a tracks. where multiple tracks crossed a roadway, receiver was placed over approximate locations of two outermost rails and centerline of roadway pavement as shown in centerline Figure 4. Each crossing was recorded as a recorded for each site. Each crossing was recorded as a separate rover file. points used this technique to replicate methods that would most likely be employed by researchers registering crossing location, researchers entered crossing's DOT-AAR While (taken from tag mounted on post) into receiver to aid in identification of number in office. Researchers also photographed each approach to each crossing. Slides crossing produced to allow VTRC staff to scan images into computer files for future use. were data collection. Overall, study concluded that GPS data collection requires minimal training or instruction. In addition, it requires negligible reading and data-keying skills. reliability of data collection was very consistent in all studies. Two problems that system adjustments by U.S. Department of Defense (DOD). latter problem did not arise often, but DOD must maintain accuracy of system. Loss of signal reception because of overhead GPS Case Studies Point Data for SMS: Highway-Railroad Grade Crossings 27 public highway-railroad grade crossings in Albemarle County (15) and City of Charlottesville (12) were registered as point data using GPS receiver. single-track grade crossing) intersects centerline of roadway pavement (Figure 3). At separate point feature, with a minimum of 120 data personnel responsible for conducting grade crossing inventory in field. 10

20 Track!i!i!i!i!i!i!i!i! iiiiiiiii i iiiiiiiill Center of Crossing Center Crossing of!!- data collection took researchers 12 hr for 27 crossings. Approximately 15 was spent at each crossing. time required to register location of crossing and min! l;i:i:i:i:i:i:i:i:i:i: Roadway CENTER OF CROSSING DETERMINATION" SINGLE TRACK FIGURE 3. Roadway CENTER OF CROSSING DETERMINATION" MULTIPLE TRACK FIGURE 4. 11

21 each approach for one crossing was 2 min. remainder of time at each photograph was spent ensuring that receivers were functioning properly, that y had lock on a location at each location represents approximately half total time required to collect data at spent of crossings. This discrepancy is primarily due to grade crossings being located on all secondary roads, usually on outskirts of county, requiring a significant amount of time to in office, first step for researchers was to download each rover file from Once receiver to PC. This process took only 30 sec to 1 min per file using GPS software. rover files were differentially corrected, y were exported to a format Once with that of UNIX ARC/INFO and imported into GIS to build a point coverage. compatible and railroad lines in Albemarle County and City of Charlottesville. Figure 6 crossings 12 grade crossings collected using GPS in City of Charlottesville. shows 45 AAH segments in Greene County were recorded as line data using GPS Each segment was collected using same method. researchers began recording receiver. at one end of segment and simultaneously entered name of segment locations party) and applicable route number. Once name and route number were (responsible researchers drove segment maintaining posted speed limit and remaining in entered, lane y started in, and stopped recording location information at or end of feature, AAH segments, was n closed, but rover file remained open. This segment. was used because of proximity of AAH segments in this county. It also allowed method researchers to keep receiver "seeing" satellites, decreasing amount of start-up time before collecting next AAH segment. required depending on length of segment, terrain encountered, availability of varied, prevailing speed limits, and or highway traffic. refore, no tree average satellites, length of time was determined. time required to register a segment's name and route number input DOT-AAR number into receiver was only 4 min per crossing. time spent to sufficient number of satellites, and that y were collecting information properly. time drive to each location. rover files were in PC, next step was to post process (differentially correct) Once To differentially correct raw rover files, researchers needed to download base station m. files from a local bulletin board. Ten base station files had to be downloaded, representing each hour that a rover file was created. In a number of situations, several rover files were created in same hour, and refore only one base station file was required to correct se files. time required to download 10 base station files was 80 min, approximately 8 min per file. process developed to complete this task is illustrated in Appendix A. Once coverage was Figures 5 and 6 were developed. Figure 5 depicts 27 public highway-railroad grade created, Line Data for Operations and Maintenance: Adopt-a-Highway Program collection of AAH segments took 14 hr. time spent collecting each segment 12

22 receiver also varied, depending on length of group's name responsible for into and route number. Essentially, time required to input an AAH segment was a segment in office, researchers' first step was to download each rover file from Once to PC. This process took only 1 to 1.5 min per file using GPS software. Once receiver correct raw rover files, researchers needed to download base station files from differentially a bulletin board. Nine base station files had to be downloaded, representing each hour local rover files were differentially corrected, y were exported to a format Once with that of UNIX ARC/INFO and imported into GIS to build a line coverage. compatible process developed to complete this task is illustrated in Appendix B. Once coverage was Figure 7 was developed, which depicts 45 AAH segments and county roads in created, Polygon Data for Compliance with NEPA" Wetland Delineation boundary VDOT mitigation wetland site in Greensville County was collected of single rover file. This wetland site itself occupies 30,403 2 m of land. receiver was taken a as completed in a manner similar to that of line data previously described. However, since this single rover file was collected in approximately 3 hr. file was n downloaded a PC and post processed using base station files downloaded from a base station in to Again, downloading of base files took approximately 8 min for each hour Charlottesville. data needed. corrected file was n grouped using PFINDER software. In this of procedure was followed for each of 70 flag locations making up file. maximum of 2 min. rover files were in PC, next step was to post process (differentially correct) m. To rover files collected data. time required to download nine base station files was 72 min, approximately 8 min per file. Greene County. to each flag marking boundary. flags were previously placed at border of wetland boundary by VDOT's Aquatic Ecology personnel. file was opened at first flag and allowed to receive signals for approximately 2 min (120 epochs). After desired number of had been collected at each flag, file was paused and receiver taken to next flag. points was taken not to overlook any hard-to-see flags, as this would result in a miscalculation of Care boundary location. After each flag had been recorded ( perimeter of wetland completely traversed) rover file was closed. collection of boundary could have been particular wetland was previously marked by flags, it was determined that simply collecting a series of points at each flag and n averaging m would be most appropriate. process, all of points collected at a particular flag (approximately 120 points at grouping were grouped or averaged to give a more accurate location value for single flag. This each) Finally, points were n joined as a single polygon, using PC-based GPS software, representing 17

23 of wetland and transferred to UNIX ARC/INFO as outlined in Appendix C. boundary of this procedure is shown in Figure 8. output Accuracy Determination measure accuracy of point, line, and polygon feature types collected, To collected se data types using process described in Methods section. researchers point data was differentially corrected and imported into UNIX ARC/INFO using similar to that of highway-railroad grade crossing commands found in Appendix commands Table 2 depicts difference in distance from known HARN location and that of A. points. Figure 9 shows HARN location and 10 GPS derived points. As identified in GPS 2 and in Figure 9, all but one of corrected GPS points are accurate to within 1.5 m of Table known location. average distance from known location is less than 1 rn (0.92 m). 2 TABLE OF GPS POINT DATA ACCURACY Point Data

24 line data were differentially corrected and imported into UNIX ARC/INFO similar to those used in AAH section and found in Appendix B. Table 3 depicts commands actual test line length. As depicted in Table 3, only one of se lines has a percent difference than 2. average length for line segments collected using GPS is m, which greater only a 0.04-m difference from test line segment. is Polygon Data 3 TABLE OF GPS LINE DATA ACCURACY actual test polygon area and each of GPS-collected polygon areas and ir corresponding differences. Figure 10 shows polygons and ir relationship to HARN site and to percent or. identified in Table 4, two of polygons had a percent difference greater than 2. each As area for polygons collected using GPS was , m which corresponds to a average Line Data using Test polygon data were also differentially corrected and imported into UNIX ARC/INFO similar commands as wetlands delineation commands in Appendix C. Table 4 depicts using difference of only 1.01 percent of that of test polygon. 25

25 4 TABLE OF GPS POLYGON DATA ACCURACY mentioned previously, problems will arise in collection of data in areas with tall As researchers experienced this phenomenon, urban canyon effect, while buildings. data at a grade crossing in City of Charlottesville. crossing was in an area collecting tall buildings in three of four surrounding quadrants (see Figure 11). researchers with required to remain at this location for an additional 15 min until four satellites rotated to a were where y were visible to receiver. only problem this posed was that time point spent at this location was significantly increased. collecting AAH segments, researchers had only a few minor problems, While of m resulting from use of receiver. Because of rural nature of Greene none researchers noted or locations with AAH signs and collected associated segments, Although this problem was not significant, it did cause a problem in knowing information. number of AAH segments in Greene County as well as adding 4 hr to data collection true process. mountain roadway. Figure 12 depicts terrain and environment of segment. This type lane terrain will not adversely affect accuracy of data collected, but it will significantly add of Test DISCUSSION Problems with Data Collection County, re were no signal disturbances caused by manmade obstructions. first problem was physically locating AAH segments. map provided by Charlottesville Residency It indicated numerous roadways as AAH segments that had no AAH signs and was not current. or roadways that were not AAH segments that had signs. While collecting indicated AAH problem associated with collection of AAH segments concerned Anor of some of segments. For instance, one segment was located on an unpaved single- location 26

26 FIGURE 11. URBAN RAIL CROSSING WITH SATELLITE VISIBILITY OBSTRUCTION FIGURE 12. ADOPT-A-HIGHWAY SEGMENT COLLECTED

27 time required to collect data because speed of vehicle carrying GPS receiver to be reduced. must resulted in at least four satellites being visible during entire collection process. collection), depending on time of year and location of site, heavy tree canopy could come Obviously, play. However, or research 8' has indicated that signals can still be received even where into canopies exist. heavy during study, receiver "saw" an adequate number of satellites to collect Twice but would not collect any information. This enigma usually continued for 20 min. n, data as soon as problem occurred, receiver began receiving signals from four visible just researchers assumed that this problem was due to DOD restoring health to satellites. time required to collect each feature type is given in Table 5. majority of spent was in initial data collection stage and during creation of ARC/INFO time in importing of DGPS in UNIX. collection of point data was more time- coverage than collection of line data. This was due primarily to additional attribute data consuming (photographs) collected for each point location. Collecting data using GPS allows for As with any type of data collection, obstacles will be identified early in process. 5 TABLE COLLECTION AND TRANSFER TIME DATA Polygon 5 hr Few problems were encountered during collection of wetland boundary. Most of site was open, and center of area was ponded. This, coupled with fact that receiver was held stationary at each flag ( receiver was not in motion as it was in line data satellites. simultaneous input of attribute data. Although this increases time required to collect field data, it can potentially save time by significantly reducing number of staff hours required to add attributes to locational data back in office. Once y have been identified, collection process will usually proceed smoothly. For Point 15 min Line 1-10 min

28 conversion of PC-based GPS data to UNIX ARC/INFO occupied a large amount of files, a significant amount of time was spent for each file, nearly 8 min each. This is station an excessive amount of time, especially when vast quantities of data are recorded considered a long period of time. This limitation is due in large part to rate at which base over modem transmits data. Should this rate increase, time required to download se station software manuals provided for GPS software and UNIX ARC/INFO did not adequate instruction to transfer corrected GPS files from PC to workstation. supply complicate matters furr, little instruction was provided concerning process to combine To files from PC to workstation. A substantial amount of time, as shown in attribute conversion process to place GPS files into a usable GIS coverage. test line and polygon coverages about HARN location were collected in Since small areas, precision needed to be increased before generating se coverages. relatively researchers changed default settings in ARC/INFO highest precision before generating coverage. double, of decimal places coverage was generating, reby making it more precise. This number in default settings does not always have to be made. change accuracy values for points collected at HARN test site were assumed to be of any point data collected using similar procedures under similar conditions. representative 13 depicts anticipated maximum GPS error range of collected grade crossings. Figure values stated by manufacturer and those found in previous research were Accuracy ends of each line segment were determined by recording only a single epoch collection, and averaging as were done for point data were not performed). From (overcollection previous research and manufacturer statements, 6 researchers assumed that error values used in this study, obstacles encountered did not pose a significant problem in examples of data collected. y only added to time required to collect data. quality Data Conversion and Transfer time for researchers. Base station files were required to differentially correct rover files collected. Since researchers had to dial into a local bulletin board to download base files will decrease. Table 5, was dedicated to creation of Appendices A, B, and C to aid VDOT and or users in from single, highest precision to This change increased allowable Data Accuracy comparable to those found in this study. Line value accuracies were better than originally anticipated. Because of method of 31

29 7.32 m be between 6 and 10 m. error values calculated were very close to those of point would data. were quite accurate, with a maximum error of 2.11 percent.- This percent difference boundaries directly related to size of area. With a true total area of just over 900 m 2, errors is However, to obtain accuracies comparable to those found here, data must collected in a similar fashion and for polygons of at least this size. It would also be extremely be to obtain more accurate data by anor method. If a digitizing or scanning method was difficult data source would have to be at a very large scale. A map at a 1:24,000 scale, for used, could potentially introduce errors of tens or even hundreds of meters. example, location calculation errors from GPS-derived values were lower than could be with most or methods of data collection. Most digitizing uses hard copy data at a obtained that limits accuracy of digital output, regardless of accuracy of original scale When this hard copy data source is transferred to a digital source, additional error is source. Center of Crossing Error Range GPS diameter circle) (4-m Typical Cross'tie ANTICIPATED GPS ERROR RANGE FOR A TYPICAL GRADE CROSSING FIGURE 13. As shown in Table 4, results of area calculation from GPS-derived polygon found were very small. 32

30 does not have errors associated with scale simply because data are GPS at a 1"1 scale. "digitized" copy source. and maintained by DOD, end users have little or owned control over evolution of using GPS to collect data. no findings of this and previous research are very encouraging for use of GPS as a collection method for GIS. Problems exist, but availability and reliability of system data on earth's surface derived with GPS for any point, wher for a point, Locations point making up part of a line, or a point making up part of a polygon, were found a collected by way of GPS are subject to system anomalies (such as an inadequate Data of satellites visible to receiver, DOD restoring health to satellites, number satellite formation) that are not in control of data collector. This unusable require recollection of data during se periods. may achieved by using mapping-grade GPS receivers are adequate for Accuracies of data for many of priority applications related to planning and collection in VDOT's GIS Strategic Plan. This type of receiver will not provide management acceptable for design purposes. accuracies depending on scale of source. For example, a 1"2400 aerial photograph will introduced, inherent error because of method of collection (distortion, pixel size, etc.). A 2.5-mm have error when digitizing will result in a 6.1-m error being added to original error of hard Evolution of GPS Technology GPS technology continues to evolve. More sophisticated receivers are being developed that will reduce errors associated with data collection. Even as se improvements are being made, price for se enhanced receivers continues to decrease. Or enhancements include ability to differentially correct data in real time. Selective availability (DOD's built-in degradation of GPS signals) may be eliminated in near future. culmination of se advancements would help make GPS feasible for more users in more applications. Conversely, however, since entire system is CONCLUSIONS have increased dramatically over just last few years. Based on findings of this study, following can be concluded: to be within 2 rn of ir real-worm location. 33