The International Federation of Congress Automatic Control Proceedings of 20th Proceedings of the the 20th World World The International Federation of Congress Automatic Control Toulouse, France, July 9-14, 2017 The International Federation of Proceedings of the 20th World Congress The International of Automatic Automatic Control Control Toulouse, France,Federation July 9-14, 2017 Available online at www.sciencedirect.com Toulouse, France, July 9-14, 2017 The International of Automatic Control Toulouse, France,Federation July 9-14, 2017 Toulouse, France, July 9-14, 2017 ScienceDirect IFAC PapersOnLine 50-1 (2017) 15627–15632 Improved Trajectory Prediction and Improved Trajectory Prediction and Improved Trajectory Prediction and Improved Trajectory Prediction and Simplification Analysis for ATM System Improved Trajectory Prediction and Simplification Analysis for ATM System Simplification Analysis for ATM System Simplification Analysis for ATM System Modernization Simplification Analysis for ATM System Modernization Modernization Modernization Modernization ∗ ∗ ∗ Eric Conrado de Souza ∗ Caio Cesar Fattori ∗ Suely Silva ∗ Eric Conrado de Souza ∗∗ Caio Cesar Fattori ∗ Suely Silva ∗ Eric Eric Conrado Conrado de de Souza Souza ∗ Caio Caio Cesar Cesar Fattori Fattori ∗∗ Suely Suely Silva Silva ∗∗ de Souza Caio Cesar Fattori Silva em Tecnologias S/A, Rua do Rócio Suely 313, 4th floor, em Tecnologias S/A, Rua do Rócio 313, 4th floor, Atech Negócios em Tecnologias S/A, Rua do Rócio 313, 4th floor, São Paulo/SP, Brazil (e-mail: ecsouza@atech.com.br; Atech Negócios em Tecnologias S/A, Rua do Rócio 313, 4th floor, São Paulo/SP, Brazil (e-mail: ecsouza@atech.com.br; ∗ Atech São Negócios em Tecnologias S/A, Rua do Rócio 313, 4th floor, Paulo/SP, Brazil (e-mail: ecsouza@atech.com.br; cfattori@atech.com.br; ssilva@atech.com.br). São cfattori@atech.com.br; Paulo/SP, Brazil (e-mail: ecsouza@atech.com.br; ssilva@atech.com.br). São cfattori@atech.com.br; Paulo/SP, Brazil (e-mail: ecsouza@atech.com.br; ssilva@atech.com.br). cfattori@atech.com.br; ssilva@atech.com.br). cfattori@atech.com.br; ssilva@atech.com.br). Abstract: Flight trajectory prediction is improved by additional modeling of flight dynamics, Abstract: Flight trajectory prediction is improved by additional modeling of flight flight dynamics, Abstract: trajectory improved by of allowing theFlight aircraft model toprediction cope with is input saturation caused bymodeling poor flight modeling. Abstract: Flight trajectory prediction is improved by additional additional modeling of intent flight dynamics, dynamics, allowing the aircraft model to cope with input saturation caused by poor flight intent modeling. Abstract: Flight trajectory prediction is improved by additional modeling of flight dynamics, allowing the aircraft model to cope cope with with input saturation saturation causeddata. by poor poor flight intent intent modeling. Accuracythe of aircraft prediction evaluation is addressed with flight Trajectory simplification allowing model to input caused by flight modeling. Accuracy of aircraft prediction evaluation isand addressed with flight flight data. Trajectory simplification allowing the model to cope with input saturation caused by poor flight intent modeling. Accuracy of prediction evaluation is addressed with data. Trajectory simplification methods are additionally considered a novel technique is proposed and implemented for Accuracy of additionally prediction evaluation isand addressed with flightis data. Trajectory simplification methods are considered aa novel technique proposed and implemented for Accuracy of prediction evaluation is addressed with flight data. Trajectory simplification methods are additionally considered and novel technique is proposed and implemented numerical investigations, yelding satisfactory results. methods are additionally yelding considered and a novel technique is proposed and implemented for for numerical investigations, satisfactory results. methods are additionally yelding considered and a novel technique is proposed and implemented for numerical investigations, satisfactory results. numerical investigations, yelding satisfactory results. © 2017, IFAC (International yelding Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. numerical Keywords: investigations, Aerospace trajectories,satisfactory Prediction results. problems, Data reduction, Aerospace control, Keywords: Aerospace trajectories, Prediction problems, Data reduction, Aerospace control, Keywords: Aerospace trajectories, reduction, Aerospace Aerospace control, control, Process Automation. Keywords: Aerospace trajectories, Prediction Prediction problems, problems, Data Data reduction, Process Automation. Keywords: Aerospace trajectories, Prediction problems, Data reduction, Aerospace control, Process Automation. Process Automation. Process 1. Automation. INTRODUCTION and Management operations and represents the core asset 1. INTRODUCTION and Management operations and represents the core asset 1. and Management operations and represents the asset of many control and planning services in these 1. INTRODUCTION INTRODUCTION and Management operations andsystem represents the core core asset of many control and planning system services in these 1. INTRODUCTION and Management operations represents the core asset many control and planning system services in these modernization programs. It isand claimed that advanced DeThere is widespread consensus, for some time now, that of of many control and planning system services in these modernization programs. It is claimed that advanced DeThere is widespread widespread consensus, forManagement some time time now, now, that of many control and planning system services in these modernization programs. It is claimed that advanced Decision Support Tools (DST) based upon TP are capable There is consensus, for some that the current approach to Air Traffic (ATM) is modernization programs. It isbased claimed that advanced DeThere is widespread consensus, forManagement some time now, that cision Support Tools (DST) upon TP are capable the current approach to Air Traffic (ATM) is modernization programs. It is claimed that advanced Decision Support Tools (DST) based upon TP are capable of reducing controller workload and, thus, for decreasThere is widespread consensus, for some time now, that the current approach to Air Traffic Management (ATM) is unable to meet expected capacity, safety, and environmencision Support Tools (DST) based upon TP are capable the current approach to Air Traffic Management (ATM) is of reducing controller workload and, thus, for decreasunable to meet meet expected capacity, safety, and environmencision Support Tools (DST) based upon TP are capable of reducing controller workload and, thus, for decreasing airspace capacity limitation, (Schuster and Porretta, the current approach to Air Traffic Management (ATM) is unable to expected capacity, safety, and environmental demands, (Enea and Porretta, 2012). Many authors of reducing controller workload and, thus, for decreasunable to meet(Enea expected safety, and environmening airspace capacity limitation, (Schuster Porretta, tal demands, andcapacity, Porretta, 2012). Many authors of reducing workload and, thus, for decreasairspace capacity limitation, (Schuster and Porretta, 2010). DSTs controller have required specific levels ofand accuracy in unable to meet expected capacity, safety, and environmental demands, (Enea and Porretta, 2012). Many authors believe that accommodation of future demands by the ing ing airspace capacity limitation, (Schuster and Porretta, tal demands, (Enea and Porretta, 2012). Many authors 2010). DSTs have required specific levels of accuracy in believe that accommodation of future demands by the ing airspace capacity limitation, (Schuster and Porretta, 2010). DSTs have required specific levels of accuracy in terms of trajectory predictions, (Paglione and Oaks, 2007), tal demands, (Enea and Porretta, 2012). Many authors believe that accommodation of future demands by the ATM systems is only possible with increased automation DSTs have predictions, required specific levelsand of Oaks, accuracy in believe that accommodation of future demands by the 2010). terms of trajectory (Paglione 2007), ATM systems is only possible with increased automation 2010). DSTs have required specific levels of accuracy in terms of trajectory predictions, (Paglione and Oaks, 2007), and therefore pose stringent accuracy performance requirebelieve that accommodation of future demands by the ATM systems is only possible with increased automation and collaboration through interoperability of flight inforterms of trajectory predictions, (Paglione and Oaks, 2007), ATM systems is only possible with increased automation and therefore pose stringent accuracy performance requireand collaboration through interoperability of Kirk, flight 2012). infor- and terms of trajectory predictions, (Paglione and Oaks, 2007), therefore pose stringent accuracy performance requirements to provide prediction services to meet their needs ATM systems is only possible with increased automation and collaboration through interoperability of flight information between stakeholders, (Mondoloni and and therefore pose stringent accuracy performance requireand collaboration through interoperability of Kirk, flight 2012). infor- ments to provide prediction services to meet their needs mation between stakeholders, (Mondoloni and and therefore pose prediction stringent accuracy performance requireto services to their needs accordingly. This dependence, it is thought, become and collaboration through interoperability ofconcepts flight 2012). information between (Mondoloni and Kirk, Hence, the need stakeholders, for modernized ATM related and ments to provide provide prediction services to meet meet will their needs mation between stakeholders, (Mondoloni and Kirk, 2012). accordingly. This dependence, it is thought, will become Hence, the need for modernized ATM related concepts and ments ments to provide prediction services to meet their needs accordingly. This dependence, it is thought, will become more outstanding with increased modernization and intermation between stakeholders, (Mondoloni and Kirk, 2012). Hence, the need for modernized ATM related concepts and systems throughout. ATM modernization is a global effort, accordingly. This dependence, it is thought, will become Hence, the need for modernized ATM related concepts and more outstanding with increased modernization and intersystems throughout. ATM modernization modernization is aa concepts global flights effort, accordingly. This dependence, it is thought, will become more outstanding with increased modernization and operability. Hence, the need for modernized ATM related and systems throughout. ATM is global effort, with worldwide implications: local and international more outstanding with increased modernization and interintersystems throughout. ATM modernization is a global flights effort, operability. with worldwide implications: local and international more outstanding with increased modernization and interoperability. systems throughout. ATM modernization is a global flights effort, with worldwide implications: local are tightly coupled almost everywhere. Additionally, Air operability. with worldwide implications: local and and international international flights The core paper objective revolves on presenting perforare tightly coupled almost everywhere. Additionally, Air operability. with worldwide implications: local and international flights are tightly coupled almost everywhere. Additionally, Air Traffic in general is largely influenced by local projected core paper objective on presenting perforare tightly coupledis almost everywhere. Additionally, Air The The paper objective revolves on performance analysis a flightrevolves trajectory predictor and its Traffic indemands general largely influenced by by local projected projected The core core paper of objective revolves on presenting presenting perforare tightly coupledis almost everywhere. Additionally, Air mance Traffic in general largely influenced local airspace and by international trends. As such, analysis of aa flight trajectory predictor and its Traffic in general is largely influenced by local projected The core paper objective revolves on presenting performance analysis of flight trajectory predictor and its integration to a post-processing trajectory simplification airspace demands and by international trends. As such, mance analysis of a flight trajectory predictor and its Traffic in general is largely influenced by local projected airspace demands and by international trends. As such, tactical and strategic system services are being revisited integration to a post-processing trajectory simplification airspace demands and by international trends. As such, mance analysis of a flight trajectory predictor and its integration to a post-processing trajectory simplification engine. These are part of an analysis and systems develtactical and strategic system services are being revisited integration to a post-processing trajectory simplification airspace demands andsystem by international trends. As such, engine. tactical and strategic services being revisited in current modernization programs, such as NextGen, These are part of an analysis and systems develtactical and strategic system services are are being revisited integration to a post-processing trajectory simplification engine. These are part of an analysis and systems development framework being devised in which accurate flight in current modernization programs, such as NextGen, These are part of devised an analysis and systems develtactical and strategic system services are revisited in current programs, such as NextGen, SESAR, andmodernization Brazil’s SIRIUS. These programs based engine. opment framework being which accurate flight in current programs, suchbeing as are NextGen, engine. These part of devised an analysis and systems development framework being devised inprovided which accurate flight predictions andare time estimates arein to a conflict SESAR, andmodernization Brazil’s SIRIUS. SIRIUS. These programs programs are based opment framework being in which accurate flight in current modernization programs, such as NextGen, SESAR, and Brazil’s These are based on full 4D Trajectory Based Operations, or TBO. The predictions and time estimates are provided to a conflict SESAR, and Brazil’s SIRIUS. These programs are based opment framework being devised in which accurate flight predictions and time estimates are provided to a conflict detection module under development and intended to be on full 4D Trajectory Based Operations, or TBO. The predictions and time estimates are provided to a conflict SESAR, andTrajectory Brazil’s SIRIUS. TheseBased programs are based on full 4D Operations, or TBO. The fundamental element ofBased Trajectory Operations is detection module under development and intended to be on full 4D Trajectory Based Operations, or TBO. The predictions and time estimates are provided to a conflict detection module under development and intended to be employed for tactical operations within the existing Air fundamental element of Trajectory Based Operations is detection module under development andthe intended toAir be on 4D Trajectory Based Operations, or TBO. fundamental element Trajectory Based Operations is thatfull airlines and the of ATM system will agree about The the employed for tactical operations within existing fundamental element of Trajectory Based Operations is detection module under development and intended to be employed for tactical operations within the existing Air Traffic Control (ATC) system, (Fattori et al., 2017). that airlines and the ATM system will agree about the employed for tactical operations within the existing Air fundamental element of Trajectory Based Operations is that airlines and the ATM system will agree about the trajectory that will be followed by an aircraft. Trajectory Traffic (ATC) system, al., 2017). that airlines and the ATM system will agree Trajectory about the employed for tactical withinet Traffic Control Control (ATC) operations system, (Fattori (Fattori etthe al., existing 2017). Air trajectory that will be followed by an aircraft. Traffic Control (ATC) system, (Fattori et al., 2017). that airlines and the system agree about prethe The aircraft trajectory that will be followed by aircraft. Trajectory model in (Fattori the TP ethas may also include additional constraints for improved trajectory that will be ATM followed by an anwill aircraft. Trajectory Controlflight (ATC) system, al.,evolved 2017). and The aircraft flight model in the TP has evolved and may also include include additional constraints for improved improved pre- Traffic trajectory that will be followed by an aircraft. Trajectory The aircraft flight model in the TP has evolved and may also additional constraints for prematured to include extended modeling in a more robust dictability, thus aiding in workload reduction for air traffic The aircraft flight extended model in modeling the TP in hasa evolved and may also include additional constraints for improved pre- matured to include more robust dictability, thus aiding in workload reduction for air traffic The aircraft flight model in the TP has evolved and may also include additional constraints for improved prematured to include extended aa more robust dictability, in workload for air traffic implementation intended for modeling prediction.in This evolution controllers. thus It is aiding envisioned that in reduction the new ATM system matured to include extended modeling in more robust dictability, thus aiding in workload reduction for air traffic implementation intended for prediction. This evolution controllers. It is envisioned that in the new ATM system matured to include extended modeling in a more robust dictability, thus aiding in workload reduction for air traffic implementation intended for prediction. This evolution controllers. It is envisioned that in the new ATM system alone is responsible for improved prediction accuracy. airlines and Air Navigation Service Providers will optimize intended for prediction. This accuracy. evolution controllers. It isNavigation envisioned Service that inProviders the new ATM system implementation is responsible for improved airlines and Air will optimize implementation intended foradds prediction. This accuracy. evolution controllers. isNavigation envisioned that inthrough the newa ATM system alone is responsible for improved prediction airlines Air Service Providers will optimize Flight intent modeling also toprediction increased businessand andIt mission trajectories common 4D alone alone is responsible for improved prediction accuracy. airlines and Air Navigation Service Providers will optimize intent modeling also adds to increased accuracy. business and mission trajectories through a will common 4D Flight alone is responsible for improved prediction airlines and Air Navigation Service Providers optimize Flight intent modeling also adds to increased accuracy. business and mission trajectories through a common 4D Accuracy, however, is not the only main concern here; trajectory information network. This entails a systematic Flight intent modeling alsothe adds to main increased accuracy. business and mission trajectories through common 4D Accuracy, however, is not only concern here; trajectory information network. This entailsa systematic Flight intent modeling also adds increased accuracy. business and mission trajectories through a aaacommon 4D Accuracy, however, is not only main concern here; trajectory information network. This entails systematic the associated flexibility of the use of to the flight model as a dissemination or sharing of aircraft trajectory data beAccuracy, however, is not the only main concern here; trajectory information network. This entails systematic the associated flexibility of use of the flight model as a dissemination or sharing of aircraft trajectory data beAccuracy, however, is not the only main concern here; trajectory information network. This entails a systematic the associated flexibility of use of the flight model as dissemination or sharing of aircraft trajectory data betrajectory predictor is further investigated. tween various stakeholders involved in ATM operations. the associated flexibility of use of the flight model as a a dissemination or sharing of aircraft trajectory data betrajectory predictor is further investigated. tween various stakeholders involved in ATM operations. the associated flexibility of use of the flight model as a dissemination or sharing ofinvolved aircraft trajectory dataoperbe- trajectory predictor is further investigated. tween various stakeholders in ATM operations. Operations range from strategic planning to tactical trajectory predictor is further investigated. tween various stakeholders involved in ATM operations. Operations range from strategic strategic planning to tactical tactical oper2. TRAJECTORY PREDICTION is further investigated. tween stakeholders involved in ATM operations. Operations from to operations, various fromrange decision to planning execution and are trajectory predictor Operations range frommaking strategic planning tophases tactical oper2. TRAJECTORY PREDICTION ations, from decision making to execution phases and are 2. TRAJECTORY PREDICTION Operations range from strategic planning to tactical operations, from decision making to execution phases and are based on the decision most recent datatoavailable. 2. TRAJECTORY PREDICTION ations, from making execution phases and are based on the most recent data available. 2. TRAJECTORY PREDICTION The ability to accurately forecast future aircraft trajectoations, from decision making to execution phases and are based on the most recent data available. based on the most recent data available. ability to accurately forecast future aircraft Trajectory Prediction (TP) is available. an important part in the The The ability to accurately forecast future trajectories is central to a myriad of ATM subsystems and trajectoservices, based on the most recent data Trajectory Prediction (TP) is an important part in the Theisability totoaccurately forecast future aircraft aircraft trajectories central a myriad of ATM subsystems services, Trajectory Prediction (TP) an important part in the ATM community vision for is modern Air Traffic Control Trajectory Prediction (TP) is an important part in the The ability to accurately forecast future aircraft trajectories is central to a myriad of ATM subsystems and services, such as the traffic load forecasting, weatherand assessment, ATM community vision for modern Air Traffic Control ries is central to a myriad of ATM subsystems and services, Trajectory Prediction (TP) is an important part in the such as the traffic load forecasting, weather assessment, ATM community vision for modern Air Traffic Control ATM community vision for modern Air Traffic Control ries is central to a myriad of ATM subsystems and services, such as the traffic load forecasting, weather assessment, conflict detection and resolution, to name a few. ATM Partially sponsored by CNPq Brazil under RHAE Program; such as the traffic load forecasting, weather assessment, ATM community vision for modern Air Traffic Control conflict detection and resolution, to name aa assessment, few. ATM Partially sponsored by CNPq Brazil under RHAE Program; such as the traffic load forecasting, weather conflict detection and resolution, to name few. ATM systems, such as conflict probe, metering and spacing, Project Grant n. 472504/2014-2. Partially sponsored by CNPq Brazil under RHAE Program; conflict detection and resolution, to name and a few. ATM Partially sponsored by CNPq Brazil under RHAE Program; systems, such as conflict probe, metering spacing, Project Grant n. 472504/2014-2. conflict detection and resolution, to name a few. ATM systems, such as conflict probe, metering and spacing, Project Grant n. 472504/2014-2. Partially sponsored by CNPq Brazil under RHAE Program; systems, such as conflict probe, metering and spacing, Project Grant n. 472504/2014-2. Project Grant n. 472504/2014-2. Copyright © 2017 IFAC 16197systems, such as conflict probe, metering and spacing, ∗Eric Conrado ∗ Atech Negócios ∗ Atech Negócios ∗ Copyright © 2017 IFAC 16197 2405-8963 © IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Copyright 2017 16197 Copyright © 2017, 2017 IFAC IFAC 16197 Peer review under responsibility of International Federation of Automatic Control. Copyright © 2017 IFAC 16197 10.1016/j.ifacol.2017.08.1900 Proceedings of the 20th IFAC World Congress 15628 Eric Conrado de Souza et al. / IFAC PapersOnLine 50-1 (2017) 15627–15632 Toulouse, France, July 9-14, 2017 air traffic advisory DSTs, and Traffic Flow Management systems, depend on provision of prediction estimates as a service, (Mondoloni and Kirk, 2012). 2.1 Flight Modeling A kinetic approach to trajectory prediction is considered: a set of deterministic, point-mass equations of motion, based on the flight dynamics presented below, was employed to model the arbitrary airliner. The Flight Model implemented in the Trajectory Predictor is a six degreeof-freedom, nonlinear dynamical model of commercial aircraft in trimmed flight, see Glover and Lygeros (2004). The resulting aircraft model is a set of continuous-time ODEs defined by Eq. 1: ż(t) = f (z(t), u(t), t), z0 = z(t0 ) (1) where f is, in general, a non-autonomous mapping between the aircraft state z, input u, time t, and the time rate of state ż. A minimal realization of the state vector z usually comprises aircraft position written in the Cartesian representation of the Earth geographical coordinates, altitude, aircraft true airspeed, heading, and aircraft mass. Aircraft engine thrust, roll angle, and wind velocity vector are considered model inputs and are lumped together in the input vector u. Model parameters are obtained from Base of Aircraft Data (BADA) 3, (Eurocontrol, 2015). Atmospheric modeling is integrated to the above aircraft flight model. This modeling provides parameters for conversion between aircraft calibrated and true airspeed figures, provides atmospheric states’ values for the computation of lift & drag forces acting on the aircraft model and provides intermediate states for determining mass variation dynamics. See also Porretta et al. (2008). 2.2 Intent Modeling The Intent model describes how the aircraft is to be flown. The intent model is as necessary as the aircraft flight model for a successful prediction process. Standard flight plan information - such as, aircraft type, onboard navigational equipment, expected route waypoints, and anticipated cruise altitude and airspeed - is insufficient for satisfactory trajectory estimation because flight plans do “not contain enough information to build from it an unambiguous rendition of the flight path in 4D”, (Klooster et al., 2010). Intent data complements the flight plan with information that can impact the predicted aircraft path, (Schuster and Porretta, 2010), including controller issued altitude and time constraints, settings for flight guidance, speed profile intent, thrust and drag performance factors, aircraft weight, and aircraft maneuvering procedure over the temporal horizon for prediction. These may vary greatly with the application operational environment and include pilot and controller preferences and objectives. Flight intent modeling here is based on the analysis of flight data, to determine aircraft rates of climb and descent, and contain estimates of Top-of-Climb and Top-ofDescent. An equally important matter concerns the speed schedule itself. In this case, aircraft speed intent is modeled by data mining flight data. The tangible advantage of this approach is that typical aircraft speed, climb and descent rates, and other figures are available to describe flight intent. These intent measures represent the best description of flight intent, along with other prediction parameters, and are introduced into the Trajectory Predictor in the form of a flight intent model. This proved to be more effective means to describe intent than the Energy Share Factor (ESF), see Schuster et al. (2012). Additional intent information is coded into the model in the form of aircraft guidance laws. Feedback loops are also in place to reject disturbances and regulate cross-track and heading deviations to zero w.r.t. a nominal trajectory given by the expected flight route. No aircraft flight speed scheduling look-up table was employed directly: the flight control system was used to regulate aircraft velocity based on intent modeling. In the early stages of research, prediction trajectories were created by inputting a sequence of route waypoints to the predictor engine. These waypoints are based on flight history (tracks) analysis and contain more than just geographical coordinates of aircraft position: altitude and speed are also provided to indicate main aircraft motion over the flight period considered. Moreover, these waypoints were transformed into continuously differentiable class functions to be used by the guidance and control laws in the flight model for input tracking and aid the trajectory reconstruction process. The prediction results presented here, on the other hand, require only discrete waypoints as intent input, and not through specific class functions, and are less dependent on flight history information. Intent modeling with data from departure and approach procedures will also be considered in future developments to enhance the flight intention information being input to the Predictor, as mentioned above. Under the speed scheduling context, trajectory prediction is, generally, posed as the following problem: Claim 1. Predict aircraft trajectory with Look-AheadTime T considering the aircraft is expected to perform the provided speed schedule. Considering that an aircraft is always able to perform the provided speed schedule is, in general, a strong prediction problem hypothesis. Instead, the proposed TP solves the more general problem: Claim 2. Predict aircraft trajectory with Look-AheadTime T by attempting to fly the provided speed schedule though limited to flight dynamics and envelope. This second prediction problem will answer “Can the aircraft model strictly fly the provided intent?” If not, it is likely the model input will saturate and the aircraft model will fly differently from what the intent model required it to. Thus, the aircraft, incidental to the modeled aircraft performance, and given mass and atmospheric conditions, may or may not fly the provided arbitrary speed schedule. This requires extra flight dynamics modeling not usually accompanying kinetic based predictors, such as the Total Energy Model (TEM). A control strategy was devised to cope with aircraft model input saturation, i.e., engine thrust saturation. During saturation, the available propulsive energy is appropriately allocated to climb and acceleration motions by some ad hoc criterion. In this case the original flight intent model provided is broken in the sense that the coupling between different intent states, 16198 Proceedings of the 20th IFAC World Congress Eric Conrado de Souza et al. / IFAC PapersOnLine 50-1 (2017) 15627–15632 Toulouse, France, July 9-14, 2017 REV Files such as required altitude and speed, will not be maintained. Current TP enables the flexibility to achieve the intent flight states, albeit in saturation, in an independent fashion. 15629 Aircraft Database Aircraft Interpreter Formal description of intent is not a sought for objective here; this step in modeling is bypassed and intent numerics directly feed the TP instead. Aircraft Intent Description Language (AIDL) can be used for this purpose, (Bronsvoort et al., 2015). Also, the sole purpose of this study is to evaluate ground-based system prediction performance. Air-ground downlink issues, such as ground/FMS trajectory synchronization, is outside the scope of this investigation. PLN Interpreter Procedure Interpreter Coordinates Pre Processor AISWeb Coordinates Interface Trajectory Predictor ATC Changes 2.3 The Prediction Process Fig. 1. The Trajectory Prediction Process. The prediction process involves the fast-time solution, or simulation, of an Initial Value Problem (IVP) with initial values z0 , yielding the state z(t) as a function of time. The time horizon for this estimate varies from problem to problem. For example, gate-to-gate prediction would involve a time horizon of many hours; while conflict detection would require flight state estimation of 20 to 40 minutes of look-ahead-time from current aircraft position. Prediction assumes the initial position and look-ahead time are known, though important sources of uncertainty. departs from SBGR towards SBRP at 11h55 with an estimated flight time of only 0h41 and a cruising flight level of FL240 at 342kn. Intent for prediction is given in the form of an extended route, a sequence of points detailing spatial, speed, and altitude rate profiles. Prediction results are, amongst many others, used to feed the conflict detection service in tactical operations. For acceptable prediction accuracy, a high-order aircraft model is used for short, long look-ahead times. Therefore, the numerical integration routines used for solving the IVP are based on a 4th order Runge-Kutta integration method with an adaptive timestep size control for integration performance accuracy and runtime efficiency. Similar methods for numerical integration in trajectory prediction have been documented in the literature, (Hadjaz et al., 2012). Figure 1 provides a schematic diagram of the subcomponents of the Trajectory Predictor. Predicting the aircraft future position is regarded as a difficult endeavor. This difficulty is related specially to the estimation of perturbations influencing its motion. Aircraft flight is affected by uncertainty in wind, for the most part, and also by errors in navigation, guidance and control. Ground speed data is used to feed the TP directly and the prediction analyses with wind data, though an important source of uncertainty, is not presented at this moment. Navigation error is outside paper scope, guidance and control are addressed with intent modeling. 3. PREDICTION EVALUATION RESULTS The prediction performance analysis considered a selection of three regular commercial flights over the Brazilian territory. The first flight, callsign XXX1111, departs from SBGO towards São Paulo (SBSP) at 11h50 (EOBT) with an estimated time of flight of 1h15 (EET) and a cruising flight level of FL390 at 450kn. The second flight, YYY2222, departs from SBCF towards SBEG also at 11h50 with an estimated flight time of 3h32 and a cruising flight level of FL340 at 462kn. This flight involves two Area Control Centers (ACC) and analysis here will cover only the ACC Brasilia branch. The third flight, ZZZ3333, 3.1 Accuracy Analyses The performance analyses employs selected spatial and temporal metrics for the comparison of TP trajectory evaluations against flight track (measured) data. The motivating objective behind this comparison is to show some level of accuracy performance the kinetic flight model is able to deliver by reproducing real flight trajectory with a small number of input waypoints as the main representation of intent, i.e., input to TP. Ryan et al. (2004) and Paglione and Oaks (2007) have presented useful definitions of metrics and related criteria, for metrics application, to the problem of trajectory accuracy evaluation. Metrics for quantifying the error of the predicted trajectory to a reference trajectory, flight tracks typically, are categorized in two groups: Spatial Errors, Horizontal (HE), AlongTrack (AE), Cross-Track (CE), Vertical Errors (VE), and Temporal Errors (TE). Two general criteria are used to employ metrics for spatial and temporal metrics; results below use the closest segment for spatial metrics and the closest point for the temporal metric. The trajectories for flights XXX1111 and ZZZ3333 posses a descent phase; flight YYY2222 does not have its descent phase analysed. Flight intent modeling captured major low frequency motions for every flight phase available. Table 1 yield RMS results for the computed spatial and temporal errors. Notice that RMS errors should be evaluated in light of flight duration times, since, due to its accumulative nature, these increase with the flight duration considered in the analysis. Hence, RMS figures for each flight instance should not be contrasted to each other directly. Similarly, in the TP context, a temporal metric would indicate flight performance for distinct aircrafts flights reaching intermediate waypoints or a final destination as a function of their adopted trajectories. The error values disclosed in Table 1 are normalized with the number of trajectory points; and are of qualitative nature only: The amount of flight intent information supplied to the predictor model is of great significance when interpreting these numbers, since they are relative to the quality of intent information 16199 Proceedings of the 20th IFAC World Congress 15630 Eric Conrado de Souza et al. / IFAC PapersOnLine 50-1 (2017) 15627–15632 Toulouse, France, July 9-14, 2017 Fig. 2. Prediction horizontal (CE, AE, HE) & vertical (VE) errors. used in each prediction. Hence, a relative importance should be given to the analysis of absolute error values, for this presentation, commensurate to the intent models provided to each flight. Table 1. Relative RMS error analysis. Callsign XXX1111 Climb Cruise Descent YYY2222 Climb Cruise ZZZ3333 Climb Cruise Descent HE(nm) 1.2946 1.4951 1.5305 0.9553 0.7810 0.5264 0.8469 1.4450 1.6090 1.6188 1.1092 AE(nm) 1.2793 1.4939 1.5145 0.9270 0.1487 0.1769 0.1383 1.4370 1.5995 1.6173 1.0943 CE(nm) 0.1824 0.0602 0.2210 0.1988 0.1068 0.1553 0.0855 0.1169 0.1360 0.0699 0.1321 VE(ft) 593.54 991.17 547.52 196.35 92.59 183.02 24.10 181.25 233.75 62.83 202.55 TE(s) 10.64 11.64 11.48 9.39 6.92 5.54 7.31 12.60 15.26 12.37 10.26 Spatial prediction errors are illustrated in Fig. 2, as histograms for the cross-track (CE), along-track (AE) and vertical (VE) errors. The horizontal error as a function of flight normalized time of flight is also depicted there. Figure 3 shows the temporal error as a function of the normalized time of flight. These results compare well with the literature. Errors tend to be greater during climb and descent, as expected: close to terminal areas where procedures are followed; en-route (cruise) prediction is easier (YYY2222). XXX1111 intent for climb can be improved. Observe, moreover, that horizontal errors peak when time errors correspondingly also reach maximums. The closest segment was the adopted criteria for these analyses, (Ryan et al., 2004). In a conceptual exercise, flight intent were also deliberately under-modeled, i.e., poor modeling was considered for their prediction. In these cases, prediction showed poor prediction performance during all flight phases, as expected, demonstrating the need for fine-tuned intent modeling for improved performance with respect to a specific metric employed for error computation. 4. GENERAL COMMENTS It is easily observed that the quality of input data directly affects trajectory prediction accuracy, this claim agrees Fig. 3. Prediction Time errors and normalized flight time. with reports elsewhere, (Mondoloni et al., 2005). Despite results with wind are not exploited here, the uncertainty related to the wind-field estimation greatly impacts alongtrack and time-of-arrival errors; this has also been observed previously, (Mondoloni et al., 2005). In contrast, the wind influence on cross-track and altitude errors are less apparent. Therefore, in order to mitigate differences between true, or observed, aircraft behavior from theoretical prediction one must provide a satisfactory uncertainty model. Intent seems to impact long term predictions more prominently than flight dynamics. The kinetic approach to TP, although flexible in terms of parametrization of a wide range of different flight conditions and intent scenarios, demands more knowledge about these same conditions and scenarios and how to best employ this knowledge to correctly parametrize the flight model. In many cases, the underlying predictor flight model is significantly sensitive to this parametrization. It is recognized, nevertheless, that through a collaborative environment for the flow of information, this demand for flight related knowledge will be supplied and that modernization of ATM systems will be ready to fulfill new operational expectations. Trajectory prediction in the context of medium-term conflict detection should consider typical look-ahead-times of 20, up to 40, minutes; see Fattori et al. (2017) for TP integration with conflict probe. However, in order to validate prediction accuracy, prediction performance are evaluated with longer flight periods. The flight model considered currently is able to cope with input saturation. A heuristic for replanning, even, of flight intent with the objective of reducing undesirable effects of saturation is being designed and tested. This is only relevant if it mimics aircraft FMS behavior. 5. TRAJECTORY SIMPLIFICATION The predictor provides trajectory estimates to the conflict probe, amongst other ATM subsystems, (Fattori et al., 2017). The trajectories are simplified before being fed into the conflict detection process, instead of a direct input, in order to remove excessive number of points which defines the trajectories themselves. This simplification decreases 16200 Proceedings of the 20th IFAC World Congress Eric Conrado de Souza et al. / IFAC PapersOnLine 50-1 (2017) 15627–15632 Toulouse, France, July 9-14, 2017 p1 net computation, subsequently to prediction, required for conflict probing. p3 5.1 The Douglas-Peucker (DP) Algorithm p2 The Douglas-Peucker (DP) algorithm (Katsikouli et al., 2014) is applied to map reduction problems by removing data, or contour points, while keeping deviations from the original small. This reduction takes into account the relevancy of a single point to the map as a whole. The relevancy factor is given by the distance of one point to the set of previous relevant points. The method goes as follows: the initial and final map points are connected (these are compulsorily relevant points). The distance between each point and the lines connecting relevant points is computed. The most relevant point are defined as those with the greatest computed distance. If the point distance is above a given threshold, this point is considered relevant and belongs to the simplified map. Point distances and lines are re-calculated and the process iterates. Figure 4 illustrates the Douglas-Peucker algorithm. p1 p3 p2 1 - Calculating Distances p1 d2 p3 d3 p2 p5 A2 p3 p2 A3 A4 p2 p2 p5 A3 Fig. 5. Visvalingam-Whyatt algorithm demonstration. a measure of relevancy. This Euclidean distance quantifies the range between one point and a virtual point located on the line segment considered at a position proportional to the times of the initial and final points. Figure 6 shows the computation of the Euclidean distance. p2',t2 p3,t3 d2 Fig. 6. The Euclidean distance definition. p5 d3 p3 p4 p2,t2 p3 A2 p1 p5 p1,t1 2 - Adding p2 and recalculating distances 2 - Removing p4 and recalculating Areas 3 - Repeting steps p4 d4 p4 p1 p5 p4 1 - Calculating Areas p5 p1 15631 d4 p4 3 - Repeting steps Fig. 4. Douglas-Peucker algorithm demonstration. 5.2 The Visvalingam-Whyatt (VW) Algorithm The Visvalingam-Whyatt (VW) algorithm (Visvalingam and Williamson, 1995) is also applied to the map reduction by removing data without losing geometric features. Differently to the DP case, which employs distances between points and lines as the criterion for relevant points determination, this second algorithm uses the computed area one point defines with its adjacent neighboring points as a measure of lesser relevancy. If the computed area attributed to a point is smaller than the corresponding areas of its neighbors and, similarly, if the computed area is inferior to a given threshold, this point is removed from the solution and the areas for the remaining points are recalculated. Figure 5 illustrates the VW algorithm. The dynamical modification for the VW algorithm, intended for trajectory simplification, has not been discussed in the literature. The proposition of the dynamic term is addressed here as the composition of the area defined by one point and its neighbors and the area defined by a pair of points with a specific external point. For trajectories given by geodesics, the center of the Earth was chosen as the common external point. Figure 7 depicts the areas considered in the computation of the dynamical term for the VW algorithm. In Fig. 7, the difference of areas A1O2 and t3−t2 A2O3, which are averaged by the factors t2−t1 t3−t1 and t3−t1 , respectively, provides the definition for the dynamical term in trajectory simplification based on the VW algorithm. p1,t1 p2,t2 p3,t3 A2O3 A1O2 O Fig. 7. Dynamic term used adopted in VisvalingamWhyatt algorithm for trajectory simplification. 5.4 Performance Comparison 5.3 The Dynamical Term The map reduction algorithm cannot be employed for trajectory simplification directly, this requires the introduction of a dynamic term to the map method, (Long et al., 2013). Map data are given by location coordinates. Alternatively, trajectories are defined by coordinates and time measures. The Douglas-Peucker algorithm is modified to incorporate this term by applying the Euclidean distance in the place of the standard point-line distance as Trajectory simplification performance evaluations were carried out by fixing a number points for the simplified trajectory and varying the thresholds parameters (distance and area). Runtime figures were logged and the (simplified) output trajectories were plotted over the original. Measuring execution time reveals agility performance during trajectory simplification. This is an important matter since the simplification process output can be used 16201 Proceedings of the 20th IFAC World Congress 15632 Eric Conrado de Souza et al. / IFAC PapersOnLine 50-1 (2017) 15627–15632 Toulouse, France, July 9-14, 2017 to improve performance for subsequent processes. Both algorithms were coded in C language and processed the same predicted trajectory. Runtime measures were obtained with the OS built-in time routines. The VW based solution underperformed for simplified trajectories with up to 7 points, though performed better with a greater number of points. For 18-point trajectories, the solution based on VW’s performed up to 5% faster than DP’s. This mixed-performance behavior, parametrized by the number of trajectory points for simplification, is due to the nature of both algorithms: area calculations are more complex than distance ones and, for each iteration with the DP algorithm, when a new point is added to the output a recomputation of distances for all points follows. In contrast, when a trajectory point is removed with VW’s based solution, area calculations occur for only its two neighboring points in each iteration. Hence, for a small number of points (≤7), DP’s solution has good performance; for trajectories with >7 points, VW performs better. Trajectory accuracy performance evaluations considered qualitative graphical analysis. The original trajectory is contrasted to the simplified trajectories obtained from the two algorithms discussed. The simplified trajectories are defined by the interpolation of the output points from the simplification process. Simplification results for 18 points, along with the original, are considered in Fig. 8. (m) (km) 5 000 640 Original VW DP 500 0 400 500 800 (km) 500 700 (km) Fig. 8. Accuracy test for methods based on VW and DP approaches: the vertical (left) & horizontal planes. Observations indicate that the VW based algorithm outperformed the other for a benchmark number of points. A second test seeking to obtain the same level of accuracy with the DP based algorithm indicated the need for over 50 additional points to match accuracy obtained with the VW based simplification. 6. CONCLUSION This note on trajectory prediction and simplification represents a continued and systematic effort on devising effective methods to address prediction accuracy requirements for future ATM demands. Future research and project development include implementation code optimization and tuning refinements for improved ATM system performance. Additional methods for flight state estimation and wind data treatment are also being considered and will be included in a forthcoming presentation. ACKNOWLEDGEMENTS Thanks to the Product Eng. and Innovations group at Atech. This research is partially funded by the CNPq/MCTI, Brazil under RHAE Program, grant 472504/2014-2. REFERENCES Bronsvoort, J., McDonald, G., Paglione, M., Young, C., Boucquey, J., Hochwarth, J., and Gallo, E. (2015). Realtime trajectory predictor calibration through extended projected profile down-link. In ATM R&D Seminar. Enea, G. and Porretta, M.A. (2012). 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