Online Positioning User Service Research Articles

The possibility of Using the Low-Cost External Antenna with Smartphone for Accurate Surveying Applications by RTX Technology

Real Time Extended (RTX) technology works to take advantage of real-time data comes from the global network of tracking stations together with inventor locating and compression algorithms to calculate and relaying the orbit of satellite, satellite atomic clock, and any other systems corrections to the receivers, which lead to real-time correction with high accuracy. These corrections will be transferred to the receiver antenna by satellite (where coverage is available) and by IP (Internet Protocol) for the rest of world to provide the accurate location on the screen of smartphone or tablet by using specific software. The purpose of this study was to assess the accuracy of Global Navigation Satellite System (GNSS) low-cost external antenna and possibility for using it with a smartphone to measure the points in Real Time Kinematic (RTK) and (RTX) modes, obtaining the same accuracy by using high-cost (GNSS) receiver with same modes. The assessment has applied through comparing the control points measured in static mode (3 to 5 hours) and corrected by Online Positioning User Service (OPUS) web-based processing software with same control points measured in RTX mode by GNSS low-cost external antenna (5 minutes). The results of an assessment were obtained horizontal and vertical location error in real time, by receiver getting the RTX correction data over the satellite link were RMS (east 41cm, north 35 cm, elevation 94 cm), that means it’s more suitable for automotive, agriculture, and forestry application, As for the RTK mode, the comparison of the differences in RTK mode between the two antennas were RMS (north 5 cm, east 6 cm, elevation 10). This result indicates that the GNSS low-cost external antenna might be very useful in accurate surveying application.

A Rapid Terrestrial Laser Scanning Method for Coastal Erosion Studies: A Case Study at Freeport, Texas, USA.

Terrestrial laser scanning (TLS) has become a powerful data acquisition technique for high-resolution high-accuracy topographic and morphological studies. Conventional static TLS surveys require setting up numerous reflectors (tie points) in the field for point clouds registration and georeferencing. To reduce surveying time and simplify field operational tasks, we have developed a rapid TLS surveying method that requires only one reflector in the field. The method allows direct georeferencing of point clouds from individual scans to an East–North–Height (ENH) coordinate system tied to a stable geodetic reference frame. TLS datasets collected at a segment of the beach–dune–wetland area in Freeport, Texas, USA are used to evaluate the performance of the rapid surveying method by comparing with kinematic GPS measurements. The rapid surveying method uses two GPS units mounted on the scanner and a reflector for calculating the northing angle of the scanner’s own coordinate system (SOCS). The Online Positioning User Service (OPUS) is recommended for GPS data processing. According to this study, OPUS Rapid-Static (OPUS-RS) solutions retain 1–2 cm root mean square (RMS) accuracy in the horizontal directions and 2–3 cm accuracy in the vertical direction for static observational sessions of approximately 30 min in the coastal region of Texas, USA. The rapid TLS surveys can achieve an elevation accuracy (RMS) of approximately 3–5 cm for georeferenced points and 2–3 cm for digital elevation models (DEMs). The elevation errors superimposed into the TLS surveying points roughly fit a normal distribution. The proposed TLS surveying method is particularly useful for morphological mapping over time in coastal regions, where strong wind and soft sand prohibit reflectors from remaining strictly stable for a long period. The theories and results presented in this paper are beneficial to researchers who frequently utilize TLS datasets in their research, but do not have opportunities to be involved in field data acquisition.

Evaluation of the Online Positioning User Service for Processing Static GPS Surveys: OPUS-Projects, OPUS-S, OPUS-Net, and OPUS-RS

AbstractThe National Geodetic Survey has developed four versions of the online positioning user service (OPUS) for postprocessing dual-frequency, static global positioning system (GPS) data. Each v...

Comparisons of OPUS and PPP Solutions for Subsidence Monitoring in the Greater Houston Area

AbstractGlobal positioning system (GPS) techniques have been applied to study land subsidence in the greater Houston area for over two decades (1993–2016). The free Online Positioning User Service ...

Interpreting OPUS-Static Results Accurately

AbstractThe Online Positioning User Service (OPUS) operated by the National Geodetic Survey (NGS) has consolidated into a very attractive tool for surveyors, engineers, and the academic community to procure precise/accurate positions from global positioning system (GPS) observations. The OPUS utility continues to be improved since it was successfully launched in 2000. In general, each update results in better reliability of the precision and accuracy of OPUS solutions. However, necessary software modifications could also introduce certain biases, some significant, complicating the interpretation of OPUS results, particularly for applications that rely on high-accuracy absolute positions. This article concentrates on the interpretation of OPUS-Static solution reports primarily in relation to the transformation of reference frames and geoid models, which are two basic scientific ingredients in practical geodetic-surveying enterprises. One-year continuous GPS observations collected at a landslide site in Pue...

Analysis of the TXDOT RTN and OPUS-RS from the Geoid Slope Validation Survey of 2011: Case Study for Texas

AbstractAs part of the Geoid Slope Validation Survey of 2011 (GSVS11), the global positioning system (GPS) was used in a variety of ways to determine the geodetic coordinates of nearly 400 passive geodetic control marks. The Texas DOT (TXDOT) real-time network (RTN) was one of the GPS positioning tools used. Both 6- and 180-s occupations were performed with the TXDOT RTN, as well as static 20-min occupations [processed using the National Geodetic Survey (NGS) Online Positioning User Service, Rapid-Static (OPUS-RS) tool], and 48+h occupations were adjusted as a network (using the NGS OPUS-Projects tool). Although the original 20-min occupations processed by OPUS-RS had an unforeseen systematic error (invalidating their use in this comparison), a direct comparison between OPUS-RS and the other techniques was still possible by subdividing the OPUS-Projects 48+h receiver independent exchange format (RINEX) files on 218 points into more than 30,000 individual 20-min segments. A comparison between all technique...

Teaching High-Accuracy Global Positioning System to Undergraduates Using Online Processing Services

ABSTRACTHigh-accuracy Global Positioning System (GPS) has become an important geoscientific tool used to measure ground motions associated with plate movements, glacial movements, volcanoes, active faults, landslides, subsidence, slow earthquake events, as well as large earthquakes. Complex calculations are required in order to achieve high-precision positions and thereby high-accuracy displacement measurements. It is difficult to familiarize undergraduates with the complex data processing within a period of one semester. Several national organizations offer free online GPS processing services. Using these online services, a GPS beginner can bypass the complex aspect of data processing and focus on applications of the high-accuracy GPS technology. This paper introduces the author's experience using Online Positioning User Service, provided by the National Geodetic Survey (NGS) and Automatic Precise Positioning Service, provided by the Jet Propulsion Laboratory (JPL) in teaching two undergraduate courses, Applications of GPS in Geosciences and Geological Hazards, at the University of Puerto Rico at Mayaguez. Two class projects, “Where is My House?” and “GPS Landslide Monitoring,” were designed to practice GPS data collection, processing, and analysis. The enrollments of the two courses were about 10 senior undergraduate students. Online GPS data processing helped both the instructor and students in teaching and learning the intricacies of GPS data processing, understanding different reference frames and coordinate systems, and familiarizing local permanent reference stations. Students who had taken the GPS classes often help professors in the geology department and other departments to survey field sites with centimeter-level accuracy.

Using OPUS for Measuring Vertical Displacements in Houston, Texas

The Houston area has been suffering from subsidence for several decades. Therefore, continuously operating reference stations (CORS) in this area may have experienced considerable vertical displacements. The Online Positioning User Service (OPUS), provided by the National Geodetic Survey (NGS), uses CORS as references in its data processing. This study investigated what effects, if any, the subsidence experienced by these CORS around Houston contributes to the accuracy of OPUS vertical results. Our OPUS results were determined from three long-term (over 10-year) blocks of continuous data using Global Positioning System (GPS) stations located in different parts of the Houston area. The OPUS results were compared with the vertical measurements from the precise point positioning with single receiver phase ambiguity (PPP-SRPA) solution implicit in the GIPSY/OASIS 6.1.2 software. This particular study indicates that OPUS achieves 1.0-cm vertical accuracy for daily sessions (24 h) in the region around Houston, which is comparable to the OPUS accuracy previously reported in other investigations. Subsidence as slow as 0.5 cm/year can be detected by analyzing OPUS results spanning 5 or more years of data. Our main conclusion is that the subsidence experienced by NGS CORS in the Houston area does not considerably affect the accuracy of OPUS vertical results. For those users who require a few centimeters of vertical accuracy for daily sessions, OPUS is a good choice, because users do not need to establish any control stations and do not need to install any GPS software packages on their local computers.

OPUS for Horizontal Subcentimeter-Accuracy Landslide Monitoring: Case Study in the Puerto Rico and Virgin Islands Region

This study demonstrates the usefulness of an approach based on the Online Positioning User Service (OPUS) provided by the National Geodetic Survey (NGS) of the National Oceanic and Atmospheric Administration (NOAA) to process Global Positioning System (GPS) data and conduct long-term landslide monitoring in the Puerto Rico and Virgin Islands region. Continuous GPS data collected at a creeping landslide site during 2 years were used to evaluate different scenarios for landslide surveying: continuous or campaign, long duration or short duration, morning or afternoon (during different weather conditions). OPUS uses the Continuously Operating Reference Station (CORS) network managed by the NGS as control points and user-collected data to solve for the position of the occupied station (rover). In July 2011, there were 19 NGS CORS sites in the Puerto Rico and Virgin Islands region. This dense GPS network provided a precise and reliable reference frame for subcentimeter-accuracy landslide monitoring in this region. OPUS static solutions (OPUS-S) for sessions as short as 4 h, and OPUS rapid static solutions (OPUS-RS) for sessions as short as 15 min, can achieve subcentimeter horizontal accuracy if the collection of data during extreme weather conditions is avoided. The uncertainty (peak-to-peak error) reported by a single OPUS-S solution differs from the “true” accuracy by a factor of 1.7 for the horizontal components and 1.3 for the vertical component. The uncertainty reported by a single OPUS-RS solution differs from the accuracy by a factor of 1.4 for horizontal components, while the uncertainty of vertical component statistically agrees with the vertical accuracy. This study also indicates that rainfall events can seriously degrade the performance of high-accuracy GPS. Field GPS landslide surveying should avoid rainfall episodes when accompanied by thunderstorms and the passage of detrimental weather fronts. Once appropriate precautions are taken, the results of this investigation show that OPUS-S and OPUS-RS are ideal alternative tools for subcentimeter-accuracy landslide monitoring.

OPUS-RS Pair Points: Case Study

Referencing small engineering surveys to the national spatial reference system (NSRS) presents advantages in terms of spatially coordinating infrastructure and facilitates the inclusion of the infrastructure in a geographic information system. In cases where the total station is the appropriate tool to conduct the survey, online positioning user service rapid static (OPUS-RS) can be employed to economically establish azimuth pair points to orient the survey to the NSRS. Using OPUS-RS coordinates as observations along with global positioning system (GPS) vectors and total station observations in a least-squares adjustment to establish the azimuth pair points adds robustness to the least-squares adjustment to isolate systematic errors. All the observations contribute to the least-squares adjustment but some observations contribute more than others do. Redundancy numbers can be used to identify those observations that contribute little to the adjustment results. By analyzing the results of three least-squares adjustments, it will be shown that under normal conditions total station observations contribute little to the overall adjustment. Under obstructed conditions total station observations contribute to the vertical precision of the azimuth pair points. OPUS-RS appears to be less susceptible to vertical biases than GPS vectors at obstructed sites.

Accuracy assessment of the National Geodetic Survey’s OPUS-RS utility

OPUS-RS is a rapid static form of the National Geodetic Survey’s On-line Positioning User Service (OPUS). Like OPUS, OPUS-RS accepts a user’s GPS tracking data and uses corresponding data from the U.S. Continuously Operating Reference Station (CORS) network to compute the 3-D positional coordinates of the user’s data-collection point called the rover. OPUS-RS uses a new processing engine, called RSGPS, which can generate coordinates with an accuracy of a few centimeters for data sets spanning as little as 15 min of time. OPUS-RS achieves such results by interpolating (or extrapolating) the atmospheric delays, measured at several CORS located within 250 km of the rover, to predict the atmospheric delays experienced at the rover. Consequently, standard errors of computed coordinates depend highly on the local geometry of the CORS network and on the distances between the rover and the local CORS. We introduce a unitless parameter called the interpolative dilution of precision (IDOP) to quantify the local geometry of the CORS network relative to the rover, and we quantify the standard errors of the coordinates, obtained via OPUS-RS, by using functions of the form $$ \sigma ({\text{IDOP}},{\text{RMSD}}) = \sqrt {(\alpha \cdot {\text{IDOP}})^{2} + (\beta \cdot {\text{RMSD}})^{2} } $$ here α and β are empirically determined constants, and RMSD is the root-mean-square distance between the rover and the individual CORS involved in the OPUS-RS computations. We found that α = 6.7 ± 0.7 cm and β = 0.15 ± 0.03 ppm in the vertical dimension and α = 1.8 ± 0.2 cm and β = 0.05 ± 0.01 ppm in either the east–west or north–south dimension.

A New Network-Based Rapid-Static Module for the NGS Online Positioning User Service - OPUS-RS

National Geodetic Survey (NGS) operates the Online Positioning User Service (OPUS) as a means to provide the GPS users with easier access to the National Spatial Reference System (NSRS). OPUS allows the users to submit their GPS data files to NGS, where the data are processed to determine position coordinates using NGS computers and software. OPUS is fully automatic, and the results are emailed back to the user, usually within a few minutes. OPUS is intended for the use in the conterminous U.S. and most territories. Currently, OPUS accepts a minimum of two hours of GPS data, with a recommendation of submitting at least four hours to improve the solution. In order to reduce the required user session duration, a rapid-static module (OPUS-RS) is currently under implementation, in collaboration with the Satellite Positioning and Inertial Navigation (SPIN) Lab at The Ohio State University. The OPUS-RS is based on the Wide Area Rapid-Static (WARS) module of the Multi Purpose GPS Processing Software (MPGPSa), and it is an implementation of the Network RTK algorithm applied in the software. The new module reduces the required session duration to 10Ð15 minutes while centimeter-level accuracy is still achievable. Presented in this paper is the first demonstration and feasibility test of the OPUS-RS. The analyses consist of a subnetwork of the State of Michigan CORS with station separations of 247Ð292 km and base-rover distances of 135Ð162 km. A 24-hour data set was post-processed in 144 sessions of 10 minutes each with 30-s data sampling rate. The ambiguity resolution success ratio, speed and reliability, along with the positioning results are analyzed. The results show that 97% success ratio was achieved. Applying a second iteration to the unresolved cases improved the success ratio to 100%. The analyses were performed on 18 February 2005 under unfavorable ionospheric conditions when a minor geomagnetic storm took place with maximum Kp = 6+. The resulting coordinate accuracy is better than 1 cm for the horizontal components and than 3 cm for the vertical one.

Heuristic Weighting and Data Conditioning in the National Geodetic Survey Rapid Static GPS Software

NOAA’s National Geodetic Survey (NGS) has developed the Rapid Static GPS software for use as the major processing engine in the OPUS-RS utility (online positioning user service—rapid static) (http://www.ngs.noaa.gov/OPUS/OPUS-RS.html). The software was written specifically to support the computation of static positions from GPS tracking sessions as short as 15min, while using reference station data from the NGS archive of continuously operating reference stations (CORS). When the reference stations are close (50km) to the user’s station, it is relatively easy to obtain an accurate solution. However, the CORS stations in the NGS archive are separated by 200km or more in many areas of the country. In this situation, much care must be taken in conditioning the data sets and in selecting appropriate weights for the observations and constraints. This paper describes methods and weights that have been found to work well for most (but not quite all) data sets, and, therefore, can be used in an automated procedure such as OPUS-RS.

Statistics of Range of a Set of Normally Distributed Numbers

We consider a set of numbers independently drawn from a normal distribution. We investigate the statistical properties of the maximum, minimum, and range of this set. We find that the range is closely related to the standard deviation of the original population. In particular, we investigate the use of the online positioning user service (OPUS) global positioning system (GPS) precise position utility, which produces three estimates of each coordinate and reports the range of these three estimates. We find that the range divided by 1.6926 is an unbiased estimate of the standard deviation of a single coordinate estimate, and that the variance of this estimate is 0.2755 σ2. We compare this to the more conventional method of estimating the standard deviation of a single observation from the sum of squares of residuals, which is shown to have a variance 0.2275 σ2.

Transforming Positions and Velocities between the International Terrestrial Reference Frame of 2000 and North American Datum of 1983

In December 2001, Natural Resources Canada and the U.S. National Geodetic Survey ~NGS! jointly adopted values for a set of 14 parameters for transforming positional coordinates and velocities between the International Terrestrial Reference Frame of 2000 ~ITRF00! and the North American Datum of 1983 ~NAD 83!. Seven of these parameters characterize the variation with respect to time of the standard seven parameters ~three shifts, three rotations, and a differential scale !. In March 2002, the NGS updated the NAD 83 positional coordinates for all continuously operating reference stations to be consistent with their corresponding ITRF00 coordinates at an epoch date of 2002.00. Also, the NGS has incorporated these adopted values for the 14 transformation parameters into software packages, such as HTDP ~horizontal time dependent positioning! for transforming positional coordinates across time and between reference frames, and OPUS ~On-line Positioning User Service! for processing global positioning system data. Both HTDP and OPUS are available through the NGS Tool Kit ~http://www.ngs.noaa.gov/TOOLS/!.