Topcon Positioning Group has released a new excavator system with local positioning system (LPS) capabilities. The X-53i LPS is designed to provide a solution for machine-controlled excavation in sky-obstructed areas.
“The system is perfect for projects such as tunnel construction or working within existing structures using a total station and prism for precision,” said Kris Mass, director of construction product management. “It’s also versatile when GNSS positioning is available with the new Topcon MC-i4 receiver. Operators can easily choose which type of sensor to best use for the project.”
The system is compatible with the new Topcon GX-55 control box — a large sunlight-viewable LCD touchscreen with integrated LED light bars designed for continuous grade reference of the bucket’s teeth. “It’s the finest graphical experience for modern machine control with customizable audible tones, all wrapped up in a lightweight package for easy transfer and storage,” Maas said.
In the Woodland cemetery Carinthia (Friedensforst Kärnten), Austria, trees are precisely measured with the rugged Algiz 10X tablet PC and a GNSS/GPS rover.
Handheld Group is making its rugged Algiz 10x tablet computer available with Geolantis surveying software and a GNSS/GPS Rover as a solution for precisely locating burial sites in for woodland cemeteries.
In woodland cemeteries, people purchase a small plot to bury ashes in an urn near the base of existing trees. Each tree has a small plaque with the names of those whose ashes are buried there. The concept treats the forest with care and enables people to buy a tree location in advance for their funeral.
One customer who has already deployed this solution is the company Bestattung Kärnten which owns a specialized woodland cemetery. To make the urn space available for the sale, the trees first need to be identified, located and registered. The high demand for forest burials in the woodland cemetery required Bestattung Kärnten to find an efficient technology for the registration and management of trees in the cemetery.
Using combination of Geolantis surveying software and the Algiz 10X tablet in combination with a GNSS GPS rover worked for the company. These precise tools are now the basis for registering of what will later be sold as urn spaces.
Once a suitable forest is reclassified as a woodland cemetery, the identification of available trees begins. The ALGIZ 10X tablet’s ability to be operated with an external GPS antenna enables the employees of the funeral company to register trees in the woodland cemetery, including related master data, at any time day or night and regardless of weather. The tablet’s 5-megapixel camera can be used at the same time to create an image catalogue.
The plans — including the register — can be extended, edited and changed at any time. The large storage capacity allows the worker to gather huge amount of data.
The 10-inch display on the Algiz 10X, which is viewable even in direct sunlight, simplifies data entry. With the Geolantis software, even non-surveyors can create an individual register for the woodland cemetery trees.
Additionally, regular tree control can be performed with the Algiz 10X. The integrated u-blox GPS receiver makes it possible to use the tablet for navigation and documentation as part of the inspection work without an external GPS/GNSS receiver.
AgStudio can now read as-applied maps and production data from Connected Farm. Previously, AgStudio software users could only read harvest data from Connected Farm.
Users with current subscriptions to AgStudio software are able to communicate seamlessly with Trimble field devices and wirelessly transfer field data, as-applied maps and production data from planters, spreaders and sprayers as well as combines for harvest data.
The recent integration taps into the new Trimble Connected Farm file transfer API, which provides data sharing access with the Connected Farm solution, and offers AgStudio software users more flexibility in importing data from an even wider variety of company systems.
“This integration with Trimble’s Connected Farm solution allows our customers greater access to information that streamlines production management,” said Ted Macy, vice president of operations at MapShots. “Whether it’s variable rate seeding, variable rate fertility, or managing harvest data, AgStudio software users now can import even more valuable information and make decisions based on activities carried out by Trimble guidance and steering systems.”
Trimble’s Connected Farm solution combines industry-leading hardware and software to increase efficiency and enable better decision making. Together, the two companies allow agricultural providers to better manage production data.
“The integration with MapShots AgStudio software fits into Trimble’s Connected Farm strategy to provide growers a more complete picture of their field activities while allowing them a choice of software tools to analyze data and make production decisions,” said Pierre-Andre Rebeyrat, strategic marketing director of Trimble’s Agriculture Division. “We are excited to welcome MapShots to the growing list of companies that have taken advantage of the Connected Farm file transfer API.”
For further information, users can contact their regional MapShots sales representative at 678-513-6093 or e-mail MapShots at [email protected].
Mobileye, a developer of vision and data analysis for Advanced Driver Assistance Systems (ADAS) and autonomous driving, has introduced a new mapping technology development called Road Experience Management (REM).
REM enables crowd-sourced real-time data for precise localization and high-definition lane data that forms an important layer of information to support fully autonomous driving.
Mobileye is engaged with General Motors to integrate REM into existing program launches in an expedited timeframe, as part of GM’s heightened partnership with Mobileye. In addition, on Jan. 5, Mobileye signed a Memorandum of Understanding with Volkswagen and announced a strategic partnership to explore and integrate REM into Volkswagen’s fleet.
The technology is based on software running on Mobileye’s EyeQ processing platforms that extracts landmarks and roadway information at extremely low bandwidths, approximately 10 kb per kilometer of driving. Additionally, backend software running on the cloud integrates the segments of data sent by all vehicles with the on-board software into a global map.
“We leveraged advanced artificial intelligence, used for creating environmental models from camera input, in order to create maps based on local coordinate systems while requiring very low bandwidth,” said Prof. Amnon Shashua, co-founder, chairman and Chief Technology Officer of Mobileye. “The low bandwidth of the model, and the fact that it requires only a camera, which is already available in most new car models as part of the trend towards growing driver assistance deployment, enables the map creation and update to be managed by a cooperative crowd sourcing mechanism.”
A third OEM customer of comparable size is expected to be announced later this year.
Shashua discussed the future of autonomous driving and road mapping at the Consumer Electronics Show in Las Vegas in January.
A GLONASS-M satellite was launched into orbit on Feb. 7 at 03:21 Moscow time from the Plesetsk Cosmodrome spaceport, reports the Russian space agency Roscosmos. The Russian Defense Ministry successfully launched GLONASS-M 51 (known as 751 in orbit) aboard a Soyuz-2.1b rocket with a Fregat upper stage.
Three and a half hours after lift-off, the satellite separated from the upper stage and ground control established communications with it. The stable telemetry link shows that onboard satellite systems are functioning normally.
According to the telemetry data received from GLONASS-M 51, the satellite is in good health. With all its mechanical subsystems successfully deployed, the satellite completed Earth and Sun acquisition. The Moscow-based System Control System and ISS-Reshetnev’s Information and Computation Center have begun satellite’s performance check-out.
Status of the GLONASS constellation, shown here, indicates that the satellite is now in the commissioning phase.
GLONASS-M 51 will replace a GLONASS satellite now operating three years past its design life.
Based on the GLONASS system’s stable operation, there has been no need to launch new satellites to augment the system, said the satellite manufacturer. The most recent launch of a GLONASS satellite was performed in 2014.
Eight GLONASS-M navigation satellites are being stored at ISS-Reshetnev Company awaiting launch.
GLONASS orbital grouping provides a solution to problems of global positioning in the interests of the Russian Defense Ministry and civilian users. Access to civilian navigation signals of global navigation satellite system GLONASS is provided to Russian and foreign consumers free of charge and without restriction.
A GLONASS-M satellite is launched in February 2016. (Photo: Russian Ministry of Defense)
The U.S. Air Force successfully launched the 12th Boeing-built GPS IIF satellite aboard a United Launch Alliance Atlas V Evolved Expendable Launch Vehicle from Space Launch Complex 41, Cape Canaveral Air Force Station, Fla., at 8:38 a.m. EST (5:38 a.m. PST) on Feb. 5.
“Today’s launch is a significant achievement in the history of GPS, as we launch the last of the GPS IIF satellites to be delivered on-orbit,” said Lt. Gen. Samuel Greaves, Space and Missile Systems Center commander and Air Force program executive officer for space. “The GPS IIF satellite performance has been exceptional and is expected to be operational for years to come.”
“This milestone is the result of the remarkable relationship between SMC, our operators within the 14th Air Force and our ULA/Boeing industry partners. Their continued tenacity and dedication to mission success ensures we continue to maintain a robust satellite constellation with modernized, more resilient GPS capabilities,” said Greaves. “A job ‘Well Done!’”
According to Greaves, this mission demonstrates the Air Force’s continued intent to deliver pre-eminent space-based positioning, navigation and timing service to users around the globe. GPS IIF is critical to U.S. national security and to sustainment of the GPS constellation for civil, commercial, and military users. GPS IIF satellites play an integral part in the modernization efforts vigorously being pursued across space, ground and user equipment to provide stronger signals and improved resiliency in the GPS constellation.
“Today’s launch marks a momentous milestone in the history of the Global Positioning System. It is the twelfth and last GPS IIF satellite and closes out nearly 27 years of launches for the GPS Block II family of satellites,” said Col. Shawn Fairhurst, 45th Space Wing vice commander, who served as the Launch Decision Authority. “As the nation’s premier gateway to space, we are proud to be part of the team providing GPS and its capabilities to the world and look forward to the future as we begin preparation for the next generation of GPS III satellites. Together with the Space and Missile Systems Center and our industry partners, we make up one team delivering assured space launch and combat capabilities for the nation.”
An Airmen-led processing team at CCAFS has processed every satellite of the series since GPS IIF-1 launched here in May 2010.
The Boeing-built GPS IIF satellites provides improved accuracy through advanced atomic clocks, a longer design life than previous GPS satellites, and a new operational third civil signal (L5) that benefits commercial aviation and safety-of-life applications. It also continues to deploy the modernized capabilities that began with the GPS IIR-M satellites, including a more robust military signal.
GPS is the United States Department of Defense’s largest satellite constellation with 31-operational satellites on orbit.
Operated by Air Force Space Command’s 50th Space Wing at Schriever Air Force Base, located east of Colorado Springs, Colo., the GPS constellation provides precise positioning, navigation and timing services worldwide as a free service provided by the Air Force, seven days a week, 24-hours a day.
Space and Missile Systems Center, located at Los Angeles Air Force Base in El Segundo, Calif., is the U.S. Air Force’s center for acquiring and developing military space systems. Its portfolio includes GPS, military satellite communications, defense meteorological satellites, space launch and range systems, satellite control networks, space-based infrared systems and space situational awareness capabilities.
The Institute of Navigation (ION) has announced the recipients of the 2016 fellow memberships and annual awards during the ION International Technical Meeting (ITM) and Precise Time and Time Interval Systems and Applications (PTTI) in Monterey, California, held Jan. 25-28.
2016 Fellows
Election to Fellow membership recognizes the distinguished contributions of ION members to the advancement of the technology, management, practice and teaching the arts and science of navigation, as well as lifetime contributions to the Institute.
Karl Kovach has been elected for significant contributions to the development of GPS, its signals, interface and specifications and performance standards.
Anthea J. Coster has been elected for contributions to the development of global GPS TEC database and for utilizing GPS measurements for ionospheric and space weather studies.
Gary McGraw has been elected for sustained contributions to the development of high accuracy and high-integrity positioning, navigation and timing technologies for a variety of military and civil aviation applications.
2015 Annual Awards
ION also presented its Annual Awards during the ITM/PTTI meeting. The awards program recognizes individuals making significant contributions or demonstrating outstanding performance relating to the art and science of navigation.
Alexander A. Trusov received the Early Achievement Award for research, development and demonstration of ultra-low dissipation inertial MEMS sensors that may enable low-cost IMUs with North-finding and inertial navigation grade performance. The Early Achievement Award is presented in recognition of outstanding contributions made early in one’s career.
Captain Nicholas Rayl received the Superior Achievement Award for performing above and beyond the call of duty navigating hostile airspace to engage a hostile AAA piece that represented a threat to aircraft. The Superior Achievement Award is presented to an individual demonstrating outstanding accomplishments as a practicing navigator.
Ramsey M. Faragher and Robert K. Harle received the Dr. Samuel M. Burka Award for their paper “Towards and Efficient, Intelligent, Opportunistic Smartphone Indoor Positioning System” published in the Spring 2015 issue of NAVIGATION: Journal of The Institute of Navigation, Vol. 62, No. 1,pp. 55-72.The Dr. Samuel M. Burka Award recognizes outstanding achievement in the preparation of a paper contributing to the advancement of the art and science of positioning, navigation and timing.
Inder J. Gupta received the Captain P. V. H. Weems Award for pioneering theoretical and experimental work on anti-jam antennas and signal processing techniques for interference suppression in GNSS receivers. The Captain P. V. H. Weems Award is presented to individuals for continuing contributions to the art and science of navigation.
James L. Garrison received the Tycho Brahe Award for contributions to developing and applying GNSS and other signals-of-opportunity, reflectometry methods for space-based and airborne remote sensing, in oceanography, agriculture, and hydrology. The Tycho Brahe Award is presented to recognize outstanding contributions to the science of space navigation, guidance and control.
Carolyn McDonald received the Norman P. Hays Award for the development and production of over thirty years of engineering tutorials in the field of satellite navigation, timing and inertial navigation; and for development and sustained support of the ION’s conference programs. The Norman P. Hays Award is given in recognition of outstanding encouragement, inspiration and support contributing to the advancement of navigation.
Tim Murphy received the Thomas L. Thurlow Award for significant contributions to Global Navigation Satellite Systems for aviation. The Thomas L. Thurlow Award recognizes outstanding contributions to the science of navigation.
Donald Mitchell received the Distinguished Service Award for his coordination between the PTTI user community and hardware developers, and contributions to the organization and operation of the PTTI meeting. The Distinguished Service Award is presented for extraordinary service to The Institute of Navigation.
Francine Vannicola received the Distinguished Service Award for representing the timing community and facilitating the incorporation of the Precise Time and Time Interval (PTTI) Systems and Applications Meeting into the ION’s meeting programs. The Distinguished Service Award is presented for extraordinary service to The Institute of Navigation.
Abstracts must be received by Feb. 15 and must be written for public release. For more information and instructions on submitting an abstract, visit the ION website.
The JNC is the largest U.S. military positioning, navigation and timing (PNT) conference of the year with joint service and government participation. For Official Use Only (FUOU) U.S. ONLY sessions will be held June 6-9 at the Dayton Convention Center in Dayton, Ohio. The U.S. ONLY CLASSIFIED sessions will be held June 9 at the Air Force Institute of Technology.
The ION Joint Navigation Conference, sponsored by the ION’s Military Division, will focus on technical advances in guidance, navigation and control (GN&C) with emphasis on joint development, test and support of affordable GN&C systems, logistics and integration.
From an operational perspective, the conference will also focus on advances in battlefield applications of GPS; critical strengths or weaknesses of fielded navigation devices; warfighter PNT requirements and solutions; and navigation warfare.
The ION JNC features more than 200 operational presentations on a diverse array of topics. It also features a technical exhibit and showcase of GNC technology products and services and operational product demonstrations.
Attendance Restricted. Conference attendance for both FOUO U.S. ONLY (June 6-8) and U.S. ONLY Secret Clearance (June 9) sessions will be screened by the Joint Navigation Warfare Center and will be restricted to U.S. ONLY.
As first reported Jan. 19, Lockheed Martin engineers have proved their design for the GPS III satellite, demonstrating that it can operate in and withstand the harsh conditions it will experience on orbit.
On Dec. 23, Lockheed Martin’s first GPS III satellite for the U.S. Air Force completed system-level Thermal Vacuum (TVAC) testing, validating the design of the entire assembled satellite. TVAC is a rigorous test designed to prove a satellite’s integrity and operational capabilities by subjecting it to prolonged cycles of simulated space temperature extremes in a special depressurized chamber.
“TVAC is the most comprehensive and perceptive test performed at the spacecraft level. If there is an issue with your design or production processes, you are going to find it here,” said Mark Stewart, vice president of Lockheed Martin’s Navigation Systems mission area. “Successful completion of this significant test validates the thermal design of the spacecraft and verifies that all spacecraft components and interfaces operate at the temperature extremes of the space environment. We credit this performance to the Back to Basics work we performed earlier and the program’s unique GPS III Non-flight Satellite Testbed.”
The first GPS III satellite undergoes system-level thermal vacuum testing. (Photo: Lockheed Martin)
In spring 2015, the GPS III satellite’s major functional components were successfully integrated to form the first complete satellite. In the fall, the new satellite also successfully completed acoustic testing, where it was pounded with sound waves to simulate the vibrations it will endure during its launch.
With eight satellites under contract, the production line is now on a steady tempo at Lockheed Martin’s GPS III Processing Facility outside of Denver, Lockheed Martin said. The first four GPS III satellites are in various stages of assembly and test with most major components — including their structure and propulsion systems, solar arrays, and antennas — already delivered.
This spring, with Harris Corporation’s delivery of its second navigation payload, the second GPS III satellite is expected to be integrated and begin environmental testing.
Components for the next four GPS III satellites are already being assembled, tested and delivered on schedule by more than 250 aerospace industry companies from 29 states.
“We have a world-class industry team supporting the development and production of GPS III for the Air Force and our nation,” continued Stewart. “I thank them for their excellent work and commitment to this program.”
GPS III will deliver three times better accuracy, provide up to eight times improved anti-jamming capabilities and extend spacecraft life to 15 years, 25 percent longer than the satellites launching today. GPS III’s new L1C civil signal also will make it the first GPS satellite to be interoperable with other international global navigation satellite systems.
Basic procedures and tools for ensuring GNNS-derived orthometric heights meet the project’s desired accuracy
So far, this series of columns has addressed the following topics: basic concepts of GNSS-derived heights (Part 1), National Geodetic Survey’s (NGS) guidelines for establishing GNSS-derived ellipsoid heights (NGS 58) (Part 2), differences between hybrid and scientific geoid models (Part 3), and procedures and tools for detecting GNSS-derived ellipsoid height data outliers (Part 4).
These four columns were meant to provide the reader with basic concepts and procedures for estimating GNSS-derived ellipsoid heights and understanding hybrid and scientific geoid models. Now that the reader has a basic understanding of GNSS-derived ellipsoid heights and geoid models, this column will discuss procedures for estimating GNSS-derived orthometric heights.
Determining valid North American Vertical Datum of 1988 (NAVD 88) published heights is the most important process when using GNSS data and geoid models to estimate GNSS-derived orthometric heights. As mentioned in Part 4, NGS has developed procedures for estimating GPS-derived orthometric heights and these guidelines are documented in NOAA Technical Memorandum NOS NGS 59. The NGS 59 guidelines are separated into three basic rules, four control requirements, and five procedures that need to be adhered to for computing accurate NAVD 88 GNSS-derived orthometric heights. This column will address the NGS 59 guidelines and methods for evaluating the results of the GNSS project.
The three basic rules are fairly simple to understand and implement, provided that the reader has followed the previous columns in this series.
Three Basic Rules for Estimating GNSS-Derived Orthometric Heights:
Rule 1: Follow NGS 58 guidelines for establishing GNSS-derived ellipsoid heights when performing GNSS surveys (Parts 2 and 4 addressed this rule),
Rule 2: Use NGS’ latest National hybrid geoid model (such as GEOID12B) and latest experimental geoid model (such as xGeoid15B) — when computing GNSS-derived orthometric heights (Part 3 addressed this rule), and
Rule 3: Use the latest National Vertical Datum — for instance, NAVD 88 — height values to control the project’s adjusted heights (this column will address this rule).
The four basic control requirements are also simple, but, in certain regions of the country, may be difficult to implement.
Four Basic Control Requirements for Estimating GNSS-Derived Orthometric Heights:
Requirement 1: GNSS-occupy stations with valid NAVD 88 orthometric heights; stations should be evenly distributed throughout project.
Requirement 2: For project areas less than 20 km on a side, surround project with valid NAVD 88 benchmarks, i.e., minimum number of stations is four; one in each corner of project. [NOTE: The user may have to enlarge the project area to occupy enough benchmarks, even if the project area extends beyond the original area of interest.]
Requirement 3: For project areas greater than 20 km on a side, keep distances between valid GNSS-occupied NAVD 88 benchmarks to less than 20 km.
Requirement 4: For projects located in mountainous regions, occupy valid benchmarks at the base and summit of mountains, even if the distance is less than 20 km.
Figure 1 depicts the NCGS Rowan County Height Modernization project discussed in Part 4. Looking at Figure 1, there are stations with published leveling-derived NAVD 88 orthometric heights distributed throughout the project (requirement number 1).
What do I mean by published leveling-derived NAVD 88 orthometric heights? This is important to note because all NGS datasheets provide the NAVD 88 height with an attribute that describes what method was used to establish their height. The following is a list of attributes used on the NGS datasheet for NAVD 88 published heights:
There are various Vertical Control sources, as specified below:
ADJUSTED = Direct Digital Output from Least Squares Adjustment
of Precise Leveling. (Rounded to 3 decimal places.)
ADJ UNCH = Manually Entered (and NOT verified) Output of Least Squares Adjustment of Precise Leveling. (Rounded to 3 decimal places.)
POSTED = Pre-1991 Precise Leveling Adjusted to the NAVD 88 Network After Completion of the NAVD 88 General Adjustment of 1991. (Rounded to 3 decimal places.)
READJUST = Precise Leveling Readjusted as Required by Crustal Motion or Other Cause. (Rounded to 2 decimal places.)
N HEIGHT = Computed from Precise Leveling Connected at Only One Published Benchmark. (Rounded to 2 decimal places.)
RESET = Reset Computation of Precise Leveling. (Rounded to 2 decimal places.)
COMPUTED = Computed from Precise Leveling Using Non-rigorous Adjustment Technique. (Rounded to 2 decimal places.)
GPSCONLV = Leveled Orthometric Height tied to GPS HT_MOD Orthometric Height. (Rounded to 2 decimal places.)
LEVELING = Precise Leveling Performed by Horizontal Field Party. (Rounded to 2 decimal places.)
H LEVEL = Level between control points not connected to benchmark. (Rounded to 1 decimal places.)
GPS OBS = Computed from GPS Observations. (Rounded to 1 decimal places.)
VERT ANG = Computed from Vertical Angle Observations. (Rounded to 1 decimal place; If No Check, to 0 decimal places.)
SCALED = Scaled from a Topographic Map. (Rounded to 0 decimal places.)
U HEIGHT = Unvalidated height from precise leveling connected at only one NSRS point. (Rounded to 2 decimal places.)
VERTCON = The NAVD 88 height was computed by applying the VERTCON shift value to the NGVD 29 height. (Rounded to 0 decimal places.)
During the design of the survey, the user should first select as many stations with the attribute of ADJUSTED or LEVELING. If there aren’t any stations in a certain area of the project with the attribute of ADJUSTED or LEVELING, then stations labeled as GPS OBS with values rounded to 2 decimal places should be occupied. The other types of NAVD 88 heights aren’t accurate enough to validate your GNSS results.
Looking at Figure 1, there appears to be a few void areas in the north and east sections of the project. Although, it should be noted that the design meets the 20 km spacing rule (Rule number 3). Figure 2 depicts the NAVD 88 published heights for all leveling-derived stations and GPS-derived orthometric heights published to two decimal places (i.e., cm level). The published GPS-derived orthometric NAVD 88 heights filled in the void areas of the project. This is the practical reality of implementing the guidelines of NGS 59.
In some areas of the United States it may be difficult to locate enough valid NAVD 88 heights in the project’s area. First, let’s define a valid NAVD 88 height. Valid NAVD 88 height values include, but are not limited to, the following: control points which have not moved since their heights were last determined, were not misidentified, and are consistent with NAVD 88. This appears to be fairly simple, but it may be difficult for some users to determine if a station has moved since the height was last determined. In addition, in some areas of the country the user may not find valid NAVD 88 benchmarks every 20 km due to crustal movement. The user then may have to perform some classical precise leveling observations to evaluate the existing NAVD 88 heights and determine the relative accuracy of the geoid model in the areal extent of the project.
This doesn’t mean that the user must perform a leveling survey such that all GNSS stations are leveled to or even perform a large leveling network survey. The purpose of the leveling is to evaluate the geoid model and properly connect to the NAVD 88. Since each case is difference, i.e., NAVD 88 height problems and geoid accuracy will vary in each region of the country, as well as each individual project accuracy requirement will be different, it is impossible to describe exactly what the user will have to do. NGS will, however, assist users when they’re planning their surveys. You can contact a NGS advisor through their Regional Advisor Program.
The five basic procedures for estimating GNSS-derived orthometric heights may appear to users to be the most complex and most difficult to understand. However, as users perform more GNSS surveys and discuss their results with others, they seem to quickly understand why these procedures are needed.
Five Basic Procedures for Estimating GNSS-Derived Orthometric Heights:
Procedure 1: Perform a 3-D minimum-constraint least squares adjustment of the GNSS survey project, i.e., constrain one latitude, one longitude, and one orthometric height value. This procedure was described in Part 4.
. Procedure 2: Using the results from the adjustment in procedure 1, detect and remove all data outliers. (NOTE: If the user follows NGS’ guidelines for establishing GNSS-derived ellipsoid heights (NGS 58), the user will already know which vectors may need to be rejected and following the GNSS-derived ellipsoid height guidelines should have already re-observed those base lines.)
The user should repeat procedures 1 and 2 until all data outliers are removed.
Procedure 3: Compute the differences between the set of GNSS-derived orthometric heights from the minimum constraint adjustment (using the latest National geoid model, for example GEOID12B, and National experimental geoid model, for example xGeoid15B) from procedure 2 above and the corresponding published NAVD 88 benchmarks.
Procedure 4: Using the results from procedure 3, determine which benchmarks have valid NAVD 88 height values. This is the most important step of the process. Determining which benchmarks have valid heights is critical to computing accurate GNSS-derived orthometric heights. (NOTE: The user should include a few extra NAVD 88 benchmarks in case some are inconsistent, i.e., are not valid NAVD 88 height values.)
Procedure 5: Using the results from procedure 4, perform a constrained adjustment holding one latitude value, one longitude value, and all valid NAVD 88 height values fixed.
As mentioned in Part 4, during the analysis of the GNSS-derived ellipsoid heights, the user needed to perform a minimum-constraint least squares adjustment and look for outliers. This ensures that the GNSS-derived ellipsoid heights meet the user’s desired standards. Now, the user must ensure that the NAVD 88 heights that are going to be used to control the final set of GNSS observations and geoid heights are valid.
Part 4 described in detail how to analyze the project’s ellipsoid heights. If the user followed the procedures outlined in Part 4, then procedures 1 and 2 were performed.
The techniques described below are meant to be fairly simple for users to implement. They are not rigorous and are not the only way to detect outliers. They will, however, assist the user in determining which NAVD 88 benchmarks are valid. Procedure 3 is simply computing the GNSS-derived orthometric heights and comparing the results with the published leveling-derived NAVD 88 heights. The set of GNSS-derived orthometric heights are obtained by performing procedure 1. Figures 3 and 4 provide the differences between the GNSS-derived orthometric heights using GEOID12B and published leveling-derived NAVD 88 orthometric heights. (NOTE: One station’s latitude, longitude, and orthometric height (Buffalo 2) was constrained in the minimum-constraint least squares adjustment. Since any of the stations with a published height could have been constrained in a minimum-constraint least squares adjustment, an average difference (a bias) computed using all of the differences was removed from each difference.)
All relative height differences between adjacent station pairs should agree within 2 cm for 2-cm surveys and 5 cm for 5-cm surveys to be considered valid NAVD 88 benchmarks. Relative height differences that do not meet this guideline should be investigated.
Part 3 discussed the difference between hybrid and scientific geoid models and that the user should use both models during their analysis of GNSS surveys. As mentioned above, Figures 3 and 4 provided the difference using GEOID12B; Figures 5 and 6 provide the differences using xGeoid15b. Tables 1 and 2 provide this information in tabular form.
Table 1. Differences between GNSS-derived orthometric heights from a minimum-constraint adjustment (using GEOID12B) and published NAVD 88 heights (GEOID12B results sorted and highlighted).Table 2. Differences between GNSS-derived orthometric heights from a minimum-constraint adjustment (using xGeoid15b) and published NAVD 88 heights (xGeoid15b results sorted and highlighted).
The reader should note that most differences in Figure 3 are less than 2 cm, but there is a several differences greater than +/- 2cm. Eight stations have differences greater than +/- 2 cm [see Table 1, column labeled “GNSS-Derived Orthometric Height (using GEOID12B) minus Published NAVD 88 Height (cm)”]. These stations should be investigated as a potential outliers.
Looking at Figure 3, the reader should notice that several stations less than 20 km apart have a relative differences greater than 4 cm.
For example, the following three station pairs have large relative height differences: [Buffalo 2 (AB6805) – Phaniel (AB6836): 4.9 cm], [V 49 (FA0151) – Phaniel: 5.6 cm], and [Row 9 (DG5715) – Phaniel: 5.7 cm]. To investigate this further, we need to introduce the scientific geoid model in the analysis. Figures 5 and 6 are plots of the differences using xGeoid15b. The user should notice that the relative differences using the scientific geoid model (Figure 5) between the same stations pairs are all less than the differences using GEOID12B (Figure 3).
For example, the relative differences between Phaniel and Buffalo 2 is 4.9 cm [(2.8 – (-2.1)] using the GEOID 12B geoid model. The relative differences between the same two stations using xGeoid15b is only 0.7 cm [4.2 – 3.5]. This implies that the hybrid geoid model may have been distorted to agree with stations that may have moved since the last time they were observed. This could be an indication that station Phaniel and/or Buffalo 2 may have moved since they were last surveyed. If so, once again, they should not be constrained in the final adjustment.
It should also be noted that only five stations have differences greater than +/- 2 cm using xGeoid15b [see Table 2, columns labeled “GNSS-Derived Orthometric Height (using xGeoid15b) minus Published NAVD 88 Height (cm)”]. However, the five outliers are significantly larger than the rest of the differences (see highlighed section on Table 2). All other differences using xGeoid15b are less than +/- 1.7 cm. These five leveling-derived heights should be investigated for possible movement before constraining their heights in the final adjustment.
As previously mentioned, looking at Figures 5 and 6, stations Phaniel and Buffalo 2 seem inconsistent with the other stations in the southern half of the project. Another potential outlier highlighted in Table 2 is station Row 3 with a difference of -3.8 cm. These stations should definitely be investigated for potential movement.
When performing constrained GNSS-derived orthometric height adjustments, it is important to determine the effect of the constraints on the adjusted heights of the unconstrained stations. If a station’s published height is not valid, then constraining that value could distort the final set of adjusted coordinates. Users should compare the differences between the adjusted heights from the constrained adjustment with the adjusted heights from the minimum-constraint adjustment. Figures 7 and 8 are plots that depict the differences between the adjusted heights obtained from a fully constrained adjustment (using GEOID12B) and a minimum-constraint adjustment.
Looking at Figures 7 and 8, the reader should notice that several of the heights of stations in the southern portion of the network have changed by more than 3 cm. More importantly, some of the closely spaced stations have large differences in relative height changes. For example, the adjusted height at station Phaniel changed -4.9 cm (this station was constrained) and its neighbor station Moose (4 km from Phaniel) only changed -3.1 cm. This means the constraint changed the height difference between Phaniel and Moose by 1.8 cm. If the constraint is valid, then the user should use it in the constrained adjustment. However, during our analysis of this project, we identified station Phaniel as a potential outlier which means that station Phaniel may have moved since it was last surveyed. As previously mentioned, if a station moved since it was last surveyed it should not be constrained because it may distort the adjusted heights around it. Saying that, it is important to maintain consistency in a National Vertical Control Network, e.g., NAVD 88, when incorporating survey data into the network. If the station is not constrained and it did not move since it was last surveyed, then all stations surrounding the superceded station will be inconsistent with its neighbors. Therefore, if a user cannot determine that the station has moved since it was last surveyed, it should be constrained in the final adjustment.
To determine the effect of constraining station Phaniel, another constrained adjustment was performed constraining all published NAVD 88 leveling-derived orthometric heights except for station Phaniel. Figures 9 and 10 are plots that depict the differences in adjusted heights due to constraining all published NAVD 88 leveling-derived orthometric heights except for station Phaniel. The plots indicate that by not constraining Phaniel, the changes in adjusted heights due to that constraint were all reduced. All differences in the area of station Phaniel are less than 3 cm and the relative height changes have been significantly reduced. For example, the relative height change involving station Phaniel and Moose was reduced from -1.8 cm [-4.9 – (-3.1)] to -0.2 cm [-1.9 – (-1.7)], and from station Phaniel to Cold, the relative height change decreased from -2.9 cm [-4.9 – (-2.0)] to -0.6 cm [-1.9 – (-1.3)]. (See Figures 8 and 10.) This is a reason why it is very important to determine if a station’s published height is still a valid NAVD 88 height.
This column discussed procedures for estimating GNSS-derived orthometric heights following NGS 59 guidelines. It provided methods for evaluating the results of the project and identifying stations with valid NAVD 88 published heights. More analysis needs to be performed to identify all the valid stations to be constrained in this project. In the next column, we will continue to analyze the changes in adjusted heights due to different constraints, compare the results to the published NAVD 88 GNSS-derived orthometric heights observed in this project, and investigate the leveling network used to establish the published NAVD 88 leveling-derived orthometric heights.
The first GPS III satellite in accoustic testing. (Photo: Lockheed Martin)
Harris Corporation will offer an all-digital navigation payload for GPS III Space Vehicles (SV) 11 and beyond.
According to Harris, the fully digital navigation payload will provide enhanced performance and enable on-orbit reprogramming. The all-digital payload expands on the advanced features of the current 70-percent digital payload that Harris provides for Lockheed Martin’s GPS III SV 1-8 satellites.
The features provide greater flexibility, affordability and accuracy compared to existing satellites and include an advanced modular design, atomic clock timing systems, radiation-hardened computers and powerful transmitters.
The new payload combines innovative digital capabilities developed by Harris and Exelis, now a part of Harris. In 2013, Exelis successfully demonstrated digital navigation signal capability in a formal preliminary design review conducted by the Air Force.
The payload also leverages the mature Technology Readiness Level 9 legacy Harris reconfigurable payload that is flying on the International Space Station and is incorporated on hosted payloads for the Iridium NEXT satellite.
Harris has more than 500 digital processors on-orbit and another 150 awaiting launch. Harris navigation payloads have been on all of the 80-plus U.S. GPS satellites launched since the 1970s, with more than 750 years of on-orbit life without a payload-related failure. Harris has delivered more than 100 digital payloads, which have performed flawlessly on-orbit, the company said.
Harris will provide a fully digital payload for GPS III satellites beginning with SV11. Shown is SV1 in testing. (Photo: Lockheed Martin)
Sokkia has introduced the latest addition to its line of field controllers for use with construction and surveying applications, the SHC5000. Operating MAGNET Field, Site and Layout software, the newest field controller is designed to provide a more versatile and faster handheld computer for GNSS receivers and total stations, with the largest screen size in the Sokkia line.
“The SHC5000 boasts a 7-inch sunlight-viewable screen, which makes it the largest in our line of field controllers,” said Ray Kerwin, director of global surveying products. “The display’s capacitive touch interface comes with finger, glove, small tip stylus and water capable options. Operators can change the screen from portrait to landscape when viewing maps or drawings, depending on which orientation is preferable.”
The SHC5000 comes with two built-in cameras. One uses an 8 MP camera with autofocus and LED flash that is designed for uses such as field photography. The second has a 2 MP camera on the front side of the unit for purposes such as video meetings.
Additional features include 64 GB of flash storage, an optional 4G LTE cellular modem, internal GPS navigation, Bluetooth and Wi-Fi, and a battery life of 10-plus hours.
