Applanix Corp. and American Aerospace Advisors, Inc. (AAAI), have agreed on an OEM supply agreement that will incorporate Applanix direct georeferencing technology into AAAI’s unmanned aerial platforms. The collaboration creates a commercially available professional-grade mapping UAV system for civilian applications such as pipeline monitoring, power line surveys and emergency-response mapping.
The availability of the system follows a series of successful test flights of AAAI’s RS-16 Unmanned Aircraft System equipped with Applanix’ DMS-UAV aerial photogrammetry payload with commercially available inertial technology. Joint teams from Applanix and AAAI planned and flew a sequence of missions to evaluate the capabilities, including the ability to provide highly accurate, directly georeferenced and orthorectified aerial imagery without the need for ground control points or aerial triangulation calculations.
The system — consisting of the airframe, its avionics, mobile ground control station, telemetry systems and the digital mapping payload — performed according to expectations and successfully produced high-quality imagery.
The announcement was made at AUVSI’s Unmanned Systems 2014 Conference in Orlando Florida, where the most comprehensive collection of unmanned systems for every domain – air, ground and marine – are on display. A video of the system can be watched here.
“The OEM supply agreement with Applanix formalizes our plans to transform the aerial mapping industry by creating an integrated, professional-grade mapping system for unmanned flight,” David Yoel, CEO of American Aerospace Advisors, said. “For civilian aerial survey projects, this can mean safer operations, lower costs and more efficient deployments while still delivering very high accuracy. We are very pleased to announce the availability of the RS-16 Direct Mapping Solution.”
“We believe this is a ground-breaking development for the airborne imaging systems market,” Joe Hutton, Director of Inertial Technology and Airborne Products at Applanix, said. “There has been a lot of attention on developing a commercial, directly georeferenced mapping solution for UAVs, and now it is a reality.”
The RS-16 with the Applanix DMS payload is available through American Aerospace Advisors directly, for sale to jurisdictions where it is permitted to fly civilian UAV systems.
Trimble has introduced the latest version of its deformation monitoring software, Trimble 4D Control version 4.3. The latest version features new optional monitoring applications — the High Rise App, the SeismoGeodetic App and the Trimble 4D Control Site Setup App for Trimble Access — to better analyze complex data communicated from a broad range of GNSS, optical, geotechnical, seismic, atmospheric and metrological sensors.
Trimble says it is continuing to expand the ways in which quantifying movement change can be automated using a range of geodetic, seismic and engineering sensors. The opportunities in automation play a significant part in effective project safety management and construction strategies, the company said. Equally important is the analysis of complex data communicated via simple visual terms in order to understand the impacts of change between disciplines.
Version 4.3 includes a dedicated page to support the functionality of the High Rise App and Composite Views for combining charts, plots and other displays. High-frequency charts, comparative bar charts, tabular and windrose analysis as well as a new visualization tool designated for in-place inclinometers and tilt meter arrays are ways to examine complex data and present findings in a meaningful way, Trimble said.
In addition to the new High Rise App, SeismoGeodetic App and Trimble 4D Control Site Setup App, the software release and apps also provide new functionality for data processing, visualization and analysis. The interactive Web Interface, Trimble 4D Control Web, provides improved multi-select control and more granularity for customizing alarms.
High Rise App: The High Rise App is intended to monitor high-rise structures during construction using GNSS and inclination sensors. Integrated processing of GNSS, total station and inclination data delivers precise and reliable coordinates on demand for stake-out jobs on structures subject to tilt such as towers and high rise buildings.
SeismoGeodetic App: The SeismoGeodetic App integrates the advantages of high-precision GNSS data and high frequency strong motion data. The data from co-located GNSS receivers and Trimble REF TEK strong motion accelerometers can now be processed in an integrated approach resulting in high-precision 3D positions up to a sample rate of 500 Hz.
Trimble 4D Control Site Setup App for Trimble Access: The Trimble 4D Control Site Setup App for Trimble Access field software allows the user to create, enhance or modify a total station site setup for Trimble 4D Control using a Trimble field controller. Once the site setup has been transferred to Trimble 4D Control, round measurements can be performed immediately without the need to run the Site Setup functionality on the server.
Trimble 4D Control version 4.3, High Rise App, SeismoGeodetic App and the Trimble 4D Control Site Setup App for Trimble Access software are available now from Trimble’s worldwide Infrastructure distribution network.
Update: The launch of the GPS IIF-6 satellite has been delayed one day due to bad weather.
Another GPS IIF satellite is expected to lift off aboard a United Launch Alliance Delta 4 rocket from Cape Canaveral at 8:08 p.m. EDT May 15 at the opening of an 18-minute launch window.
The satellite, designated GPS IIF-6 and built by Boeing, is one of the next-generation GPS satellites, incorporating improvements to provide greater accuracy, increased signals, and enhanced performance for users. According to Boeing, each GPS IIF satellite has:
greater navigational accuracy through improvements in atomic clock technology.
a new civilian L5 signal to aid commercial aviation and search and rescue operations.
improved military signal and variable power for better resistance to jamming in hostile environments.
a 12-year design life providing long-term service and reduced operating costs.
an on-orbit, reprogrammable processor that can receive software uploads for improved system operation.
GPS IIF-6 will be the United Launch Alliance’s fifth launch of 2014 and 82nd overall. It also will mark the 26th flight of the Delta IV launch vehicle since its inaugural flight in November 2002.
VectorNav Technologies has introduced its VN-300 dual-antenna GPS-aided inertial navigation system (GPS/INS). A follow-on product to the VN-100 IMU/AHRS and VN-200 GPS/INS, the miniature, high-performance VN-300 enables a wider range of applications through the incorporation of GPS compassing techniques.
The VN-300 can be used in a wide variety of industrial and military applications, and is well suited for size, weight, power, and cost (SWAP-C)-constrained applications such as unmanned vehicle systems; antenna, camera and platform stabilization; heavy machinery monitoring; robotics; and primary or secondary flight navigation, among others. The VN-300 will be on display and available for review at VectorNav’s booth #330 at AUVSI in Orlando May 13-15.
Incorporating the latest MEMS sensor technology, the VN-300 combines 3-axis accelerometers, 3-axis gyros, 3-axis magnetometers, a barometric pressure sensor, two GPS receivers, and a low-power microprocessor into a rugged aluminum enclosure about the size of a matchbox. When in motion, the VN-300 couples the position and velocity measurements from the onboard GPS receivers with measurements from the onboard inertial sensors to provide position, velocity, and attitude estimates of higher accuracies and with better dynamic performance than a standalone GPS receiver or Attitude Heading Reference System (AHRS).
The dual GPS receivers incorporated into the VN-300 provide the added benefit of accurate True North heading measurements when the sensor is stationary through the use of GPS compassing techniques, the company said. The VN-300 is designed for applications that require a highly accurate inertial navigation solution under both static and dynamic operating conditions, especially in environments with unreliable magnetic heading and good GPS visibility.
VN-300 Differentiating Features:
The VN-300 has small size, low weight, and low power requirements.
With Development Kits priced around $5k USD, the VN-300 is a fraction of the cost of similarly performing dual-antenna GPS/INS systems and is competitively priced with other MEMS-based GPS/INS systems that do not provide the dual-antenna moving baseline RTK features.
The GPS compass feature coupled with the GPS/INS capabilities on the VN-300 enables applications that require high-accuracy position, velocity, and attitude measurements under both static and dynamic operating conditions.
The algorithms on board the VN-300 enable applications to seamlessly transition between static and dynamic operations without having to collect extended stationary measurements or perform specific dynamic maneuvers in flight for attitude alignment.
The VN-300 incorporates a “True INS Filter” that does not force any requirements on alignment of the sensor to the velocity direction of a platform or specify the orientation of the sensor for initial alignment.
“The VN-300 is unique in that it provides a complete, high performance GPS-aided navigation solution under both stationary and moving conditions, all in a miniature and cost-effective package,” said VectorNav President, John Brashear. “By addressing some of the most difficult issues users face when trying to integrate an inertial navigation system — high cost; large size, weight and power; unreliable magnetic environments; and restrictive operating requirements — the VN-300 will enable an unprecedented number of applications.”
The Leica iCON CC55 controller is part of the Leica iCON portfolio.
Leica Geosystems now offers the Leica iCON CC55 controller, a versatile and rugged PDA with a 3.5-inch color display, as part of its iCON construction portfolio. The handheld controls Leica iCON sensors, runs the iCONstruct field software, and has a QuadraClear sunlight readable display and a fast 1-GHz processor.
The smaller Leica iCON CC55 handheld controller, as well as the seven-inch Tablet PC Leica iCON CC65/66 field controller, are both fully integrated into Leica Geosystems’ iCON portfolio of hardware and software solutions. It runs the Leica iCON build or site software to display and connect measured points for as-built data capturing or to lay out points and construction lines directly from the digital construction plan. The controller provides flexible options for data communication and an extensive data storage.
The Leica iCON CC55 can be used to control the Leica iCON robot total stations, enabling one-person operation, saving time and increasing productivity for construction layout tasks and as-built checks, the company said. The optional Long-Range Bluetooth allows communication with the iCON robot 50 at distances of more than 350 m/1150 feet. Alternatively, the iCON CC55 can be used as a data logger with the Leica Builder manual total station. Together with the versatile Leica iCON gps 60 SmartAntenna, the iCON CC55 creates a compact and light-weight GPS rover system.
The iCON CC55 runs the state-of-the-art Windows Embedded Handheld 6.5 operating system and comes with 256MB NAND Flash memory and 8 GB of extended storage, enabling extensive data process and storage capacity. An internal WLAN module and Long-Range Bluetooth offer users impressive distance communication, the company said, and the longer life 5.6Ah battery lets users easily complete a full day’s work. The iCON CC55 also comes equipped with a 5-MP camera so users can document their construction projects.
Visual Intelligence has announced that its iOne Software Sensor Tool Kit Architecture (iOne STKA) is available for purchase or licensing by manufacturers of unmanned airborne vehicles (UAVs) who want to deliver an integrated UAV/geospatial imaging solution to customers.
Capturing high-resolution imagery for applications in engineering, construction, urban planning, military missions and other uses is a significant emerging market for UAV manufacturers, and Visual Intelligence’s iOne STKA makes it possible to bring high-resolution geospatial sensors to UAVs, the company said. By purchasing or licensing Visual Intelligence’s geospatial imaging platform, UAV companies can meet emerging demand for geoimaging solutions that combine the benefits of UAVs with the imaging capabilities of a geoimaging platform.
iOne STKA provides the technology foundation to configure a variety of multi-purpose sensors, including miniaturized 2D/3D applications, for the emerging UVS and mobile/handheld markets. The iOne STKA received the Geospatial Forum 2013 World Technology Innovation in Sensors Award, is the first to be considered for NEANY’s Arrow UAV, and is field-proven by the commercial large-format 2D/oblique/3D multipurpose metric mapping systems iOne IMS, iOne Stereo, and iOne n-Oblique.
With the iOne STKA, the same UAS/UAV sensor system architecture can be used for agricultural and forestry mapping, pipeline or corridor monitoring, utility assessments, aerial surveys, research, persistence surveillance and other metric 2D/3D professional applications. The iOne STKA is a modular multipurpose sensor platform reconfigurable for UAVs of any size. With the iOne STKA, UAV manufacturers are no longer limited to offer monolithic, single purpose DSLR type cameras. Using the iOne STKA technology, UAV end users can economically collect high-quality color or infrared NADIR, oblique, or video imagery as well as co-mount and co-register e.g., LiDAR and thermal sensors using the same system architecture.
“By providing UAV manufacturers and end-users with one reliable and performing end-to-end standard digital sensor system solution for MANY applications, we are empowering our customers with a more efficient and standard technology foundation and paradigm to grow their business, enhance their products, and maximize their return,” said Visual Intelligence President and CEO Dr. Armando Guevara.
At the core of the iOne STKA is Visual Intelligence’s Patented Advanced Retinal Camera Array (ARCA). Developed using open systems and object-oriented software engineering principles, the ARCA is “encapsulated” with a rich set of advanced proprietary software methods that integrate camera components. The ARCA enables the collection of different types of imagery, fused in one pass, producing low-cost, extremely accurate, high-resolution products. It also enables unprecedented array-based collection and functional scalability sensor fusion. The arrays made of these varied imaging devices perform like a single camera, producing one single metric, radiometrically and geometrically correct image, or set of co-registered and fused images; such as a Virtual Frame, of higher accuracy, resolution and quality than DSLR-based monolithic cameras.
Adds Guevara, “UAV manufacturers can take advantage and offer bundled with the iOne sensors Visual Intelligence’s advanced computing technology for fast cloud-based basic and advanced actionable information product generation. As a fully automated solution (from the sensor to the cloud), the iOne STKA includes processing software that uses streamlined workflows and processes imagery faster with multicore/multithreaded/GPU computing technology, making it easy to quickly produce and analyze products in a device-content eCosystem environment. This technology/business model is designed to provide UAV manufacturers and users recurrent ROI.”
UAVs built using sensors based on the iOne STKA have the following features and advantages:
Strong digital obsolescence resilience, extending the useable life of the system while improving operational efficiencies and reducing operating costs for an even better ROI.
In the field:
Collection scalability
Functional scalability
Sensor reconfiguration, e.g. increase collection or functionality as needed or per mission requirements.
Large cross-track and FOV collection through smaller aperture (ARCA enabled).
Ability to collect different sources of metric imagery that can be fused in one pass.
Sensor fusion: Ability to co-mount and co-register in a “small and tight packaging” the EO capability with any other EO or active sensor such as LiDAR, Thermal, IR, etc.
The iOne STKA software architecture is normative across all ARCA-based products; that is, the software is the same for different array configurations or sizes. This reusable component approach yields economies of scale in the manufacturing and use of multipurpose UAV/sensor configurations.
Europe’s next two Galileo satellites are unloaded from the Boeing 747 cargo aircraft at Cayenne. The two satellites are scheduled to be launched together by Soyuz from Europe’s Spaceport this summer.
The first two Galileo Full Operational Capability (FOC) satellites arrived safely at a clean room in Kourou, French Guiana, at 20:00 on Wednesday, May 7, in preparation for launch this summer.
Named “Doresa” and “Milena,” the two Galileo FOC satellites arrived at the Félix Éboué international airport in French Guiana at 02:00 local time. They spent the day in an airlock to acclimatize before being taken to their new home, the S1A clean room, where they could be safely unpacked to begin the launch campaign.
Europe’s two latest Galileo navigation satellites touched down at Europe’s Spaceport in French Guiana packed safely within protective and environmentally controlled containers. The satellites were carried across the Atlantic aboard a 747 cargo carrier, according to the European Space Agency.
Manufactured by OHB in Bremen, Germany, with navigation payloads contributed by Surrey Satellite Technology Ltd. in Guildford, UK, these satellites – the first of 22 full-capability models — had spent several months at ESA’s Technical Centre, ESTEC, in Noordwijk, the Netherlands, where they underwent exhaustive testing in simulated space conditions.
“Adam”, the third Galileo FOC satellite is currently undergoing testing under space conditions at ESTEC. The fourth Galileo FOC satellite, “Anastacia,” will begin final testing at OHB in Bremen before being shipped to ESTEC. The Galileo satellites are named for the children who won a painting competition organized by the European Commission in 2011.
After successfully passing the Flight Readiness Review (FRR) last week, Doresa and Milena were released for shipment to the French overseas department. “Thanks to the good collaboration between the participating industrial teams and the experts at the European Space Agency ESA as our customer, OHB was able to successfully finish the FRR,” says OHB’s Director of Navigation Wolfgang Paetsch who will be personally overseeing the launch preparations in Kourou.
On May 5, the two satellites left on a pair of lorries for Frankfurt Airport in Germany, from where they flew the following evening. After landing in French Guiana, the satellites were driven to the clean room. The pair will be launched together aboard a Soyuz rocket, joining the four Galileos already in orbit. This initial quartet — the minimum number needed for achieving a position fix — has demonstrated the overall system works as planned, while also serving as the operational nucleus of the coming full constellation.
“Similar arrival scenes should become familiar over the next couple of years,” said Giuliano Gatti, Head of ESA’s Galileo Space Segment Procurement Office. “These first two Full Operational Capability satellites are effectively preparing the way for the rest of the constellation, allowing the final validation of assembly, testing and launch preparation procedures. A steady stream of satellites is foreseen, coming from OHB to ESTEC for acceptance testing and then on to French Guiana. Thanks to the preparatory work done with these pioneer satellites, future Galileos will be processed more rapidly.”
The definition, development and in-orbit validation phases of the Galileo programme were carried out by ESA and co-funded by ESA and the EU. The Full Operational Capability phase is managed and fully funded by the European Commission. The commission and ESA have signed a delegation agreement by which ESA acts as design and procurement agent on behalf of the commission. OHB System is the industrial prime contractor responsible for the total of 22 Galileo FOC satellites.
The two Galileo FOC satellites were enclosed in protective, air-conditioned containers for their flight.“Doresa” and “Milena” head to the clean room.The two satellites in the clean room.Dorese and Milena rest side by side in clean room S1A.
TerraStar is offering GNSS manufacturers revenue sharing opportunities, including the possibility to launch their own precise GNSS augmentation services via endorsed rebranding of TerraStar services as a reseller. According to TerraStar, this will provide an attractive recurring service revenue stream to GNSS manufacturers that was not previously available in the industry.
TerraStar is a brand name of TerraStar GNSS Ltd., which is a wholly owned subsidiary of Veripos Ltd. Following the acquisition of its parent company by Hexagon AB in March, it will continue as a neutral and independent provider of satellite delivered precise positioning augmentation services for land and nearshore markets. It is already well advanced in plans to expand its service offering, the company said.
Gary Wilcock, general manager of TerraStar, renewed the company’s commitment to resellers, integrators and end customers at the Munich Satellite Navigation Summit, held in March. “TerraStar will remain an open system available to all current and future partners,” Wilcock said. “The TerraStar service will remain available to all partners who have a valid contract on a perpetual basis for as long as long as the services continue to be delivered. We intend to be a long-term partner for our customers.”
Walter Steedman, CEO of Veripos Ltd. Added, “All partners will be treated on a level playing field. Strict information firewalls will be maintained for all TerraStar dealings with different business partners so that all can be assured that market or other sensitive information remains confidential.”
GAINS-10 provides accurate inertial navigation in the presence of mechanical shock, transient platform vibrations and extreme magnetic interference. It features high speed, synchronous sampling of all inertial systems combined with high rate coning and sculling compensation and is fully calibrated across temperature.
“The GAINS-10 delivers precise performance in complex environments,” said Jim Lackemacher, Group vice president of Sparton’s Defense & Security Engineered Products. “Sparton’s GAINS-10 provides flexible integration options and platform customization.”
High-speed synchronous sampling of all inertial sensors
Customizable on-board high speed digital filtering
Sculling and coning compensation
High-speed data logging capability to off-board uSD card
Ruggedized, shockproof design, with proprietary seals that allow barometric pressure sensing combined with IP67 performance
Low power consumption with power management functionality (Sleep Mode)
Interface to external GPS receiver
External data interface via Multi-GPIO connectivity
Powerful user programmable customizations via NorthTek(TM) Forth interpreter
Sparton AUVSI 2014 Events Schedule: Sparton Navigation and Exploration will be featured at the “Beyond the Booth” showcase Wednesday, May 14th at 11:30am (EDT).
Throughout the AUVSI show, Sparton will host in-booth presentations along with live demonstrations.
Carrier Phase Compensates for Wind and Wave Motion
Limited landing area as well as interference due to wind disturbance and wave motion make shipboard landings of unmanned aerial vehicles (UAVs) extremely difficult. Use of UAVs at sea can enhance the efficiency of intelligence gathering and surveillance, and could also increase long-range air-strike capability. To successfully land aircraft in such a challenging environment requires a high-precision navigation system; this prototype applies RTK measurements.
By Chiu-Jung Huang and Shau-Shiun Jan
UAVs can perform functions such as surveying, imaging, detection, sensor work, rescue, and geographic information systems (GIS) data collection. The exploitation of UAVs with portable launching and recovery systems using an automatic guidance equipment can enhance their flexibility in many practical applications. In particular, UAVs can achieve great effectiveness from launch and recovery aboard ships at sea. However, the landing area is narrow on a ship, and interference related to the maritime environment due to wind disturbance and wave motions varies greatly, making maritime UAV landings quite difficult. Recovering these aircraft in such a rapid-dynamic environment requires a high-precision UAV navigation system.
Generally, UAVs use a differential GPS (DGPS) aiding station to continuously transmit positioning correction information during landing approach; this method can provide about 0.7 to 1-meter accuracy. However, shipboard landings require more stringent accuracy. According the Joint Precision Approach and Landing System (JPALS), the requirements of shipboard landing include vertical accuracy on the order of 0.3 meters, and the requirement for the vertical protection level is 1.1 meters. To fulfill these accuracy requirements, we have chosen the real-time kinematic (RTK) technique. Recently, researchers have studied the use of RTK satellite navigation. The Boeing Unmanned Little Bird program has been examining shipboard launch and recovery using related navigation techniques.
The accuracy of using RTK navigation is 1 centimeter + 1 part per million.
Figure 1. Flow chart for software-in-the-loop.
Since development of shipboard landing is costly in terms of time and many resources, including human resources, this research is an attempt to evolve a software-in-the-loop (SIL) simulation system to analyze the accuracy of using RTK for landing navigation. The SIL system uses the MATLAB Simulink interface becasue of its helpfulgraphic user interface and block diagrams. A flowchart of the SIL system is shown in Figure 1.
The simulated RTK message provides the navigational data used as the analysis results from the experiments. To ensure the stability of the landing process, the aircraft models were control by a linear quadratic Gaussian regulator (LQG), which is able to reject the environmental disturbances encountered in the landing process. The ship motions were simulated using the factors and the model formulated by the International Towing Tank Conference. A combined position error consisting of the aircraft controls and ship motions was calculated and then fed back to the RTK navigation message.
RTK Performance
RTK navigation provides high positioning performance in the range of a few centimeters; the technique can eliminate main errors, including ionospheric and tropospheric errors and satellite clock errors, among others. A base station and a rover station can cover a service area of about 10 to 20 square kilometers. The data transition should be in real time using a wireless VHF or Wi-Fi modem.
Because data for shipboard landings are difficult to acquire, the navigation message in the SIL was simulated using experiments involving a variety of conditions. In this article, four kinds of experiments were included to help verify the availability and reliability of using RTK information as a navigational message.
We started with a basic kinematic experiment, which was simply used to assess the RTK performance. Next, a relative positioning experiment was conducted to ensure the RTK relative positioning accuracy was adequate. After that, an antenna reversal experiment was designed in order to understand the ship’s swing effect in which aircraft altitude might cause a lack of common view satellites. Finally, an antenna forward flip experiment was conducted intended to show the different RTK positioning results for a variety of sea state effects.
All of the experimental data were collected by a workshop computer through a program data file. The analyses of the results included the mean, standard deviations of positioning error, unavailable RTK percentages and the positioning accuracy when RTK was unavailable. All of the analysis results were imported to the SIL simulation using the Gaussian random variable model.
Figure 2. Kinematic experimental setup.
Kinematic Experiment. The base station setup included an antenna, tripod, and receiver. The rover station setup included a portable vehicle with a battery, antenna, and receiver placed as shown in Figure 2. The data were transmitted and received using a wireless modem for which the transmitted rate was 115200 bps. The receiver was connected to a laptop used as a workshop to monitor satellite quality and collect the data. The region in which the experiment took place is shown in Figure 3: on the roof of the Aeronautics and Astronautics department building at National Cheng Kung University in Taiwan. The red star is the known position of the base station. The broken rectangular red line is 25 meters by 10 meters along which the moving rover station moved clockwise.
Figure 3. Kinematic experimental region.
However, it is difficult to show the true positions of the experiment. In this article, we tried to get the true position by using a linear regression method which used the time, t, as the explanatory variable and the position, y(t), as the dependent variable. The linear regression used the past five epoch positions as the dependent variables by which to obtain the linear polynomial, and the fifth position was put into the polynomial to get the position error. For example, in order to calculate an error at t=4, the position results from t=0 to t=4 must be taken into Equation (1) to form the second order polynomials with parameters P, Q, and R
(1)
The experimental results are shown in Figure 4, which is the ENU positioning error, and Table 1 shows the analysis error mean and standard deviations. The experimental results show that the horizontal positioning accuracy is 0.037 meters (95 percent).
Figure 4. ENU error results for the kinematic experiment.Table 1. Positioning results for the kinematic experiment.
Relative Experiment. This experiment had one base station as before and included two rover stations which were placed on a T-bar, the relative distance being known, on a portable cart as shown in Figure 5. The region of the experiment is shown in Figure 6, where the star marks the location of the base station, with the rover station moving along the black arrow.
The relative error was calculated using a known distance, 0.72 meters, to compare the two rover station positions. Figure 7 shows the relative results of the experiment for which the mean value and standard deviations were recorded in Table 2. In this experiment, only about 4.5 percent of the positioning results failed to meet the requirement of 0.3 meters.
Figure 7. Relative error results.Table 2. Positioning results for the relative experiment.
Common-View Satellite Experiment. Aircraft landing altitude and the ship’s swing motion caused by the state of the sea might affect GNSS information received by the antenna. This experiment had one base station and one rover station at fixed positions as before, but we attempted to flip the antenna of the base station toward the north by 80 degrees, as shown in Figure 8, and the rover station changed direction according to Table 3. The antenna directional change of 80 degrees were chosen for the extreme case that the base station and rover station could experience completely different satellites in view.
Table 3. Common view satellite experimental setup for antenna.Figure 8. Common view satellite experimental setup.
Results of the experiment are shown in Figure 9, in which the vertical lines indicate antenna directional changes. For this experiment, every change is 30 seconds. This experiment demonstrates that the position performance definitely varies. The position analysis is shown in Table 4, which shows a horizontal error of 0.116meters (95 percent).
Figure 9. ENU results of the common view satellite experiment.Table 4. Positioning results for the common view satellite experiment.
Sea-State Experiment. In this experiment, one base station and one rover station were required in a fixed position, but the rover station changed the direction of the antenna, as shown in Figure 10, where the angle of x is decided according to the sea state in Table 5. On the other hand, the antenna changing toward a different direction simulated the swing motion of the boat.
Figure 10. Swing experimental setup.Table 5. Antenna angle in the swing experiment.
The experimental results shown in Table 6 are the mean values, and Table 7 shows the standard deviations. The simulation provides the analysis results in order to authenticate the integration simulations. The results show that the sea state slightly influences RTK positioning.
UAV and Ship Motion Simulations
During shipboard landing processing, many complicated conditions must be taken into account, including crosswinds, an air-wake model, wind gusts, and deck motion. The ship deck motion and crosswind effects are two key factors that further increase the difficulty of ship-borne operations.
For this reason, the UAV controller must have anti- interference features. An LQG controller is able to reject the environmental disturbances encountered during landing in a lateral motion. For the ship deck motion, the chosen spectrum (the International Towing Tank Conference, or ITTC two-parameter spectrum) was used as the power spectrum of the sea waves to be simulated.
Aircraft Simulation. The aircraft was in the simulation, the SP.X-6, was designed by the Remotely Piloted Vehicle and Microsatellite Research Laboratory of National Cheng Kung University (see opening photo and cover). For the longitudinal motion, a combination of a linear quadratic integral (LQI) controller and a Kalman filter in the inner-loop system was used to control the vertical velocity and height mainly using an elevator. For the lateral motion, the LQG autopilots were designed with guaranteed robustness properties that allowed quick return to the designed point.
The SP.X-6 aircraft state functions are shown in Equation 2, in which the x, u, y, w, and v mean the system state vector, input, measurement, process error vector, and the measurement error, respectively. A, B, C, and K refer to the system state matrices, which can be evaluated by the system identifications that are derived by using the subspace identification to obtain an initial model. After that, the initial model will feed into the recursive prediction error method algorithm in order to arrive at further refined models.
(2)
Figure 11. Linear quadratic Gaussian regulator block diagram.
After obtaining the aircraft’s model, the LQG controller is used, a block diagram for which is shown in Figure 11 and for which the close-loop dynamic is given by Equation 3. The means the estimated states are feedback by which to form the optimal control law, u=−K. The y means the output command with the LQG variables F, G, K, and L.
(3)
The aircraft landing controls were divided into the longitudinal and lateral dynamics. For the longitudinal dynamics, the landing command was the vertical discrete height. In the case of the lateral dynamics, the stable condition was used when disturbances were encountered.
Up till now, navigation of SP.X-6 relied solely on the GPS signal. Using RTK technique for the landing process will enhance navigation accuracy. The navigation method is the point-to-point guidance law illustrated in Figure 12.
Figure 12. The point-to-point guidance law.
The basic concept of the point-to-point guidance law can be derived from the aircraft initial position A and the target position B in two-dimensional coordinate frame at every epoch. Desired heading angle θT and the distance between two points d can computed at each control loop via Equation 4.
(4)
The navigation signal used in the simulation is of 20 Hz.
Deck Motion Simulation. Variations in waves are formed by the wind, and waves do not propagate only in one direction; the other direction will also affect wave propagation. The wave always is set as a stationary random process for the purpose of processing. The Longuet-Higgins model assumes that random waves are composed of many different wavelengths and harmonic amplitude superposition. Assuming the wave travels in a fixed direction, the peaks and troughs of the wave lines are parallel to each other and perpendicular to the forward direction of the waves, which are called two irregular waves or crested waves. Crested waves cause greater ship motion. The crested wave model indicates that point a at t epoch on a random sea wave height can be expressed as Equation 5, where ai-th represents harmonic waves with ωi frequency and εi initial condition.
(5)
It can be seen that the wave function can be expressed as a superposition of individual harmonics, so as long as waves establishing harmonic amplitudes and harmonic frequencies can be simulated in order to create the wave model. In this research, the amplitudes and the initial conditions are obtained from the sea wave spectrum of the ITTC model:
(6)
Four different sea state conditions were designed, as shown in Table 8 in the integrated simulation. Using the parameters from the spectrum analysis and the frequency divide method, the sea wave simulation could be obtained. Figures 13 and 14 show the simulation results of sea state A. Figure 15 shows all four state spectrum simulations results, and Figure 16 shows the sea wave height.
Figure 13. Sea State A spectrum.Figure 14. Sea State A wave height.Figure 15. Wave spectrum simulation results.Figure 16. Wave height simulation results.
Integrated Simulations
In the integrated simulation, first the health of the RTK information was examined, and then, according the environment parameter settings, sea wave simulations were conducted. Subsequently, the aircraft landing process errors were presented using the experimental positioning analysis.
The integrated simulation system is shown in Figure 17; it can be divided into three parts. The first part is the sea state options shown in the black line region, and the sea wave change is displayed and the maximum changing rate is calculated after the sea state option is selected. The second part is shown in the green line region that is the landing analysis which includes RTK health status, ENU error size. The last part is the landing animation which is enclosed in the red line region.
Figure 17. Integrated simulations graphic user interface.
Four sea-wave height simulation statuses can be selected, and the chosen sea state can be used to determine the corresponding landing environment, as shown in Figure 18, which illustrates the ship motion simulated by the wave height.
Figure 18. Sea wave change.
RTK health information was simulated according to the experimental results in Table 9, in which the RTK information unavailability was 1.1 percent. A random Gaussian number was used to simulate the health of the RTK satellite information.
After the sea-wave simulation and the RTK health simulation, the second concern was the landing process simulation. The landing process simulation has two conditions, namely the “normal landing” condition and the “landing with common-view satellite problem” condition. The normal landing process errors were presented using the Sea State Experiment results, while the landing with common-view satellite problem process errors was simulated by the result of Common View Satellite Experiment positioning analysis.
For example, a ship was traveling at a velocity of 10 m/s in East, and an aircraft was cruising at a velocity of 20 m/s toward the East. The initial position of the ship was at (ES, NS, US) = (200, 0, 0) and the aircraft was at (EA, NA, UA) = (0,150,100). In the landing process, the desired heading angle and the distance to the waypoint were evaluated every epoch. The simulated landing process example is shown in Figure 19; the blue line is the ship’s trajectory and the red line indicates the aircraft’s trajectory.
Figure 19. The simulated landing process example.
The guidance accuracy includes the control accuracy and the navigation sensor measurement accuracy. In the simulation result, the control accuracy (that is, controller error) was neglected. Therefore, the error for the landing process becomes only the navigation sensor measurement error which was the RTK error in this article. Users have the options to add different controllers as well as the controller error in the simulations.
The landing positioning error was simulated using the imported analysis results in the correspondence sea state included in the RTK status shown in Figure 20 and the landing ENU errors are shown in Figure 21.
Figure 20. RTK state simulation results.Figure 21. The ENU errors of the simulated landing process example.
Red stars in Figure 20 indicate the warning window when the simulated RTK statuses were unhealthy. For example, the 114th, 126th, 169th and 240th epochs in Figure 21 indicate that RTK data is unavailable during this time simulation. The unhealthy RTK signal might cause interruptions in navigation service in the landing process, as shown as the red stars in Figure 21. For the epochs with red stars, the simulated position results were exceeding the performance requirement for RTK shipboard landing. When this situation happened, the monitoring system might raise a flag to the aircraft’s guidance system not to use the RTK signal for landing at this period of time. Excluding these unhealthy RTK epochs, the simulated landing errors were well met the performance requirement for RTK shipboard landing, as shown in Figure 22.
Figure 22. The ENU errors of the simulated landing process after excluding the unhealthy RTK results.
An overall simulation result is illustrated in Figure 23, when the successful landing message was shown in a pop-up window, the landing information of the whole landing process would be shown in the graphic user interface.
Figure 23. Example simulation result.
Conclusions
Experimental results showed that 99 percent of the horizontal positioning was in the range requirement of 0.3 meters. Using the common view satellite experiment and the sea state variation experiment conducted in this study, the limitations of RTK positioning can be understood. Monitoring the RTK status can provide high-quality accuracy with regard to guidance of the landing process. We hope that the results of this study will become a reference for building a shipboard landing system in Taiwan.
Manufacturers
All of the experimental data were collected by a workshop computer through a NovAtel (www.novatel.com) Connect program data file. The base station setup included a NovAtel GPS-703-GGG antenna with a Sokkia tripod and the NovAtel Propak-V3 RT2-G receiver. The rover station setup included a portable vehicle with a battery, a NovAtel GPS-703-GGG antenna and the NovAtel Propak-V3 RT2-G receiver.
Chiu-Jung Huang received her B.S. degree from National Cheng Kung University (NCKU) in Taiwan. She is currently studying for her M.S. degree in aeronautics and astronautics at NCKU.
Shau-Shiun Jan is an associate professor of aeronautics and astronautics at NCKU. He directs the NCKU Communication and Navigation Systems Laboratory (CNSL). His research focuses on GNSS augmentation system design, analysis, and application. He received his Ph.D. degree in aeronautics and astronautics from Stanford University.
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Dave and Arnold Bansemer prepare the X100 for the survey.
Surveying an open-pit mine can be a hazardous undertaking. To obtain accurate volume measurements, it is necessary to pick up edges, known in the industry as “toes and crests,” as well as heaps. These are important features, since they provide a way to verify the current shape of a mine; but in light of increasingly stringent safety regulations and penalties, some companies refuse to let the surveyor get too close to such areas. Surveying the site from the air is an effective solution to this challenge.
It’s also a cost-effective solution. Namibian Mining Survey Services (NMSS) estimates that using an unmanned aerial system (UAS) can save more than 95 percent in mobilization costs, that is, bringing in resources from outside the country to conduct a lidar/photogrammetric survey. Believing UAS to be an important part of the future of surveying, NMSS had been investigating the technology for some time, and a recent project provided the perfect opportunity to try it out.
NMSS selected the Gatewing X100 for the job based on a demo at a platinum mine, where the results closely tracked those of a previous lidar survey.
The Project
The project was to survey a portion of Abenab Mine, a vanadium-lead mine owned by South West Africa Company and located just west of Tsumeb. The mine had been closed in the 1960s, but feasibility studies were underway to see if it would be viable to reopen the operation. Mine management needed to know volumes of all waste and tailings dumps, slimes, dams, and open-pit excavations. The main pit was roughly circular, about 60 meters deep and 120 meters across. Two smaller pits were covered in fairly thick vegetation but had enough ground showing to provide an accurate shape.
The survey area was approximately 100 hectares. The flying height was set at 150 meters in order to provide a ground separation distance of 5 centimeters. Ground control points (GCPs) were constructed from 1-meter lengths of masonite cut into 10-centimeter-wide strips; painted bright red, the strips were designed to provide 20 x 2 pixel coverage on the images. A total of 10 GCPs were set out in strategic positions covering a wide range of elevations, with points on top of the dumps, on undisturbed ground level, and in the pits. The points were fixed from existing control on the UTM34S coordinate system, by fast static techniques.
Launching the X100
The X100 prepares for flight.
Based on the Gatewing training received, basic photogrammetry principles and a few trials, NMSS determined that 9 a.m. to 3 p.m. was the best time to fly in order to avoid shadow. The flight area, including a previously surveyed area that would serve as a check, covered 140 hectares. Assuming favorable wind conditions, NMSS expected to cover the area on a single flight.
Arriving on site at 7 a.m., Dave Bansemer of NMSS started setting out the GCPs while his colleague performed the fast static survey. By 10 a.m., all GCPs had been placed and fixed. Having identified a suitable take-off and landing spot (a farm road), they proceeded through the pre-flight and flight checklist, and then launched the X100 at 11 a.m.. After completing the flight in around 35 minutes, with some turbulence at the 150-meter flying altitude, the X100 landed safely, albeit short of the goal, in an open area.
Once the data was downloaded, the team returned to Tsumeb to begin the processing. They started with the post-processing of the GCPs, and then moved to the coordinates obtained in the photo-control identification process. NMSS used Gatewing Stretchout Pro software for the photogrammetrical processing.
After specifying the coordinate system and identifying the GCPs, number-crunching began; the processing ran for around seven hours before the final point cloud and orthomosaics were created. The mean horizontal error was 3 centimeters and the vertical error was 9 centimeters, well within the error budget.
Results
Aerial image of the X100 survey.
The first check was to see if all areas had been covered. NMSS then checked the point cloud against the previous survey. The tie-in was perfect. Some gaps in the point cloud seemed to correspond with tree canopy areas; to ensure complete accuracy, the team resurveyed a few areas using a spatial station.
NMSS learned some important lessons from using UAV technology for survey, which Bansemer lists for the benefit of future users:
Make sure you have enough control. It is sometimes difficult to place your control points exactly in the corners of your flight and one in the center, as the actual flight is influenced by wind direction and the shape of the flight may change accordingly. Put down more points than recommended.
Make sure that your ground control point size is relevant to your flying height. You will not be able to identify a 10-centimeter wide strip if you fly at 300 meters.
Check the completeness of the job before you leave the area.
Make sure there is sufficient area for a safe landing. Bansemer recommends at least a 300-meter strip, taking obstacles into account in the event of a short landing.)
Manufacturers
The fast static techniques described were carried out with Trimble R6 GPS systems. Re-survey was done with the Trimble VX spatial station. The Gateway X100 is manufactured by Trimble.
Leica Geosystems now offers the 
The Leica iCON CC55 can be used to control the Leica iCON robot total stations, enabling one-person operation, saving time and increasing productivity for construction layout tasks and as-built checks, the company said. The optional Long-Range Bluetooth allows communication with the iCON robot 50 at distances of more than 350 m/1150 feet. Alternatively, the iCON CC55 can be used as a data logger with the Leica Builder manual total station. Together with the versatile Leica iCON gps 60 SmartAntenna, the iCON CC55 creates a compact and light-weight GPS rover system.
