The Designing and Realizing of the Satellite Navigation Simulation System

8/3/2019 The Designing and Realizing of the Satellite Navigation Simulation System

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The Designing and Realizing

of the Satellite Navigation

Simulation System

Visualization Software

Tao Liu, Yushan Zhao and Shijie Xu

School of Astronautics

Beihang University, BUAA

Beij ing 100191, China

[email protected]
mailto:[email protected]:[email protected]


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Abstract

In order to visualize the satellite navigation simulation

system, the framework of a distributed satellite navigation

simulation system composed of multi-platform systems was

analyzed. The composition and the functions of the satellite

navigation simulation system visualization software were

illuminated. Based on MFC, presented the designing and realizing

methods of the system information display program and the 2D

display program. The Vega Prime program designing methods,


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using the Visual C++, were introduced, and also the structure, the

designing and realizing methods of the 3D display program were

proposed. Based on OpenGL, Vega Prime and Visual C++, using

the designing and developing methods discussed in this paper,the satellite navigation simulation system visualization software

was developed. Practical application of the software shows that

the visualization scheme proposed here is entirely feasible for

practical engineering application.

I. INTRODUCTIONModeling and simulation plays an essential role in the designing stage of

the aerospace engineering. An accurate and vivid simulative description of a

system provides the design engineer the possibility to expedite the design

process. The visualization software, based on visual reality technology, can

show the working states and mission progress of an astronautic system

intuitively to users, and help them gain the general information about the

system quickly, and is a useful tool for the design and analysis of the

astronautic system.

Until now, in china, almost all the visualization software for aerospace

engineering are developed for one given mission, without flexibility, as in [1-

3]. And the spacecraft simulation software developed by foreign commercial

companies, e.g. Satellite Tool Kit (STK), comprehensive but not accurate

enough for some special tasks. Take the satellite navigation system serving

for ground users for example; the visual effect of STK is not good enough.


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Under the background, the satellite navigation simulation system visualization

software was developed, which has three kinds of functions, namely system

information display, 2D display and 3D, could visualize realistically all of the

working states of the satellite navigation simulation system and the whole

procedures it serves for users. The software has sufficient flexibility and could

be used for other aerospace visualization mission after little change.

This paper discussed the structure of the satellite navigation simulation

system and the functions of its subsystems To satisfy the needs of the

satellite navigation simulation system, the satellite navigation simulation

system visualization software was designed, which is composed of three

programs, namely the system information display program, the 2D display

program and the 3D display program. The design of the functions, the

developing procedures, the data structures and the realizing methods of the

system information display program as well as the 2D display program, basedon the Graphical Device Interface (GDI) of Microsoft Foundation Class

(MFC), were presented. Then the techniques to design Vega Prime programs

based on the Visual C++ were introduced, and also the functions, the

structure, the developing procedures and realizing methods of the 3D display

program were proposed. Finally, by simulating the process of navigating

multiple users, this satellite navigation simulation system visualization

software supplied vivid display effect, and it validated the feasibility of the

designing methods and techniques discussed here.

II. THE STRUCTURE OF SATELLITENAVIGATION SIMULATION SYSTEM

In space mission simulation, a whole satellite navigation simulatIon

system consists of multiple subsystems: navigation satellite simulator,

constellation simulator, telecontrol and telemetry system simulator, user

simulator, visualization software, data server and so on, as in [4].

Navigation satellite simulator is used to simulate all the subsystems of a

navigation satellite in semi-physical and mathematical manners.

Constellation simulator can complete the mathematic simulation of the

constellation, like the signal coverage percentage of the constellation,


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communications between the satellites of the constellation, the analysis of the

navigation characteristics, and so on.

Telecontrol and telemetry system simulator is used to simulate the

management of the data flow of the satellite navigation system, the sending

and management of the telecontrol instructions, the processing and

management of the telemetry data.

User simulator is used to generate the simulation data of the tracks, the

attitude, the running states of all kinds of users which move on the ground, or

fly in the air, or else sail the oceans. The visualization software provides a

method to visualize all of the working states of the satellite navigation

simulation system and verify the whole system in a visual manner. At the

beginning of the virtualization simulation, across the local Ethernet, the

visualization software firstly associates its virtual reality objects with thesimulation data in the database of the data server, and then the software

receives packets from the data server and drives the virtual reality

objects and updates the display.

All the subsystems above communicate and are synchronized with each

other through data server. Simultaneously, the data server also is responsible

for the data stream of the satellite navigation simulation system under control,

and has to preside over parameter setting for all of the simulation

subsystems. These subsystems compose a distributed simulation condition

as shown in Fig. 1.


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III. THE DESIGNING AND REALIZING OFTHE

VISUALIZATION SOFTWAREAs described in the introduction, the satellite navigation simulation system

visualization software is composed of three programs, the system information display

program, the 2D display program and the 3D display program. The functions, the

structures, the designing and realizing methods of those programs will be discussed in

detail in this chapter.

A.System Information Display Program1)function

This program is used to display the working information of the simulation

system, including data sources, simulation time, and configuration information

and so on. In order to improve visual effect and the flexibility of the program, itprovides a control library, which contains text control, curve control, radar control,

and other basic controls. Utilizing the control library, users can design the most

appropriate visual interfaces according to their requirements.

2) The Design of Control Classes

In order to manage controls efficiently, the interface designing module is

designed and embedded in the program as a dynamic-link library (DLL). Pleaserefer to [5] for more details about DLL. The module encapsulates different types

of controls, and interface functions for modifying the control properties. The

structure of those control classes is shown in Fig. 2.


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In accordance with object-oriented programming methods, all the controls

and their interface functions are derived from the base class named

CBaseControl, which provides a basic public data set and a set of functions

which supports such operations as adjusting the location, size and other

visualization properties of controls, updating the controls' states, and so on. Butthose functions of CBaseControl class are virtual and are not defined yet. All

control classes derived from CBaseControl, for example, CMeterControl class for

meter control and CCurveControl class for curve control, must provide the

implementations of those virtual functions according to their own characters, by

overloading the virtual member functions of the base class. As an illustration, the

virtual function, Show (CDC* pDC), used to redrawing controls, has been

differently implemented in different derived control classes. Besides virtual

functions, the control classes also contain their own unique attributes and

operations.

3)structureThe system information display program is designed based on MFC. The

Device Context (DC) and GDI are used. Please refer to [5] for more details about

MFC, DC and GDI. By Windows message-mapping machinery, the program can


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update and redraw various controls simultaneously via the view class in the

program, to achieve visualization capabilities.

During the simulation process, the program is required to not only interact

with the user, but also receive simulation packets across the Ethernet. Therefore,

the program uses multi-threaded architecture. The first thread, called main

thread, is started when the program is initiated, then creates the MFC frame

window, after that users can design and save the visual interface which is used

for the display of the system information. The design process is as follows. First,

create a blank display interface, add controls and modify the controls' properties,

and then, design the layout of the visual interface. After that, establish the

mapping of control set to data-base data set, and then the system information

interface is ready for displaying. The other thread, started in the main thread, is

network client thread, which is made to receive packets and transmit useful data

to the main thread via the shared memory. The working procedures of the twothreads are shown in Fig. 3.


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B) 2d display programThe 2D display program is employed to draw planar images, such as the

world map, the ground tracks, the coverage areas and the covering characters of

the satellites or the constellation. Moreover, the program is also able to display

the working states, orbit parameters and attitude parameters of various

spacecrafts.

The designing and realizing methods of the 2D display program are simIlar

to those of the system information display program, also using the DC as well as

the GDI of MFC and via Windows message-mapping machinery to fimsh ItSfunctions. Fig. 4 Illustrates the basic processing flow of the 2D display program.

This program has two threads, the display thread and the network client thread.

As shown in Fig. 4, the relationship between the two threads likes that of the

system information display program. The GDI plotting loop is the core of the 2D

display thread, and it responds to the user's inputs and uses the network packets

to carry out the main functions of the program, such as drawing ground tracks,

coverage areas of the satellites, drawing communicatIOn lmks between the

ground stations and the satellites; besides, it makes use of the inside calculating

module to finish the calculation and display of the covering characters of the

satellites or the constellation.

To keep the properties and operations for the objects that need to be

plotted, the C++ classes have been designed, as shown m Fig. 5. The

CBaseObject class is the base class which defines the general properties of all

objects, such as name, position as well as data identification and so on. The

CMobileObject class derived from the CBaseObject is designed for the moving

objects, and it has functions of updating the properties and plotting, but those

functions are virtual functions. The implementations of them are provided by the

classes derived from the CMobileObject class; for instance, the CSatellite classis used to keep properties related to satellite, and provides functions for drawing

the orbits, the coverage areas and so on. The CGroundStation class keeps

properties for ground stations.


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c) 3d display program1)function

This program has the following functions: the 3D display of the movements

of satellites, users (e.g., cars, planes, ships) and so on, which are built in 3D

models; providing multiple scenes and various viewpoints display abilities

building on the fundament of the 3D model library; could switch among the multi

scenes, including: the launch phase of satellite, the working phase of satellite in

orbit, the phase of the navigation constellation working in orbit and serving the

users. The 3D display program also provides multi-window display for a certain

simulation stage, in order to observe the simulation process from various

viewpoints simultaneously.

2)structure

The 3D display program is a Vega Prime display program based on MFC, so

when the program starts to run, it requires thee Vega Prime to start a thread for

scene rendering, Which is independent from the user thread, as in [2]. Except

for the two threads mentioned above, this program still needs to begin a network

client thread to receive the simulation data. The framework of the program is

shown in Fig. 6.


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The 3D display program transmits the packets and user' s controlling

instructions to the Vega Prime thread via the user thread, and then the Vega

Prime thread completes the rendering of the 3D objects as well as the controlling

of the movements of those objects, using the scene rendering interface functions

provided by Vega Prime. The scene rendering effects are shown to users via the

3D scenes in the view window. The program based on MFC could respond to

keyboard and mouse messages, and that is what makes it is possible for the user

to control the display of the 3D scenes by inputting the controlling instruments

according to the operation of simulation.

Fig 7 gives the basic processing flow chat of the program. The program finishes

the tasks related to the display of the Vega Prime scenes in a separate thread.

By this way, the scene rendering and processing speed could be accelerated;

furthermore it could alleviate the burden of scene display for the user thread, so

the responding to user's operations speeds up. The user thread is mainly

responsible to respond to the messages from computer systems. Because the

network client thread and the Vega Prime thread are separated, it is necessary

that the program provides shared memory for the two threads to share mutual

data with each other, and moreover, the message passing machinery is used to


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pass the user control instructions received by the user thread to the Vega Prime

thread.


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3)class designOn the basis of the structure design and the process analysis, in order to

realize all of the functions mentioned above, the 3D display program needs many

classes. The relationships among the main classes are shown in Fig. 8. As seen

in Fig. 8, the chasses in the dashed frame are Vega Prime classes which are

defined and realized by the Vega Prime, and the others are user-defined.

Among all the user-defmed classes, the CDataBase class is the base class,

which defines the general properties of all the objects, such as the name, theposition and so on. The CObject class, the CObserver class and the CDofDbj

class are derived from the CDataBase class, and they are used to keep the

information about 3D objects, viewpoints, and DOF nodes, respectively. The

CScene class defmes all of the properties needed to render 3D scenes, such as

the name, the locations and some Vega Prime objects. The CObsMgr class,the

CObjMgr class, the CDofMgr class and the CSceneMgr class, called controlling

classes, could control the viewpoints, the 3D objects, the DOF nodes and the 3D

scenes respectively, by the function call of Vega Prime API. Based on OpenGL,

the CVpOpenGL class is developed to get some special rendering effects, like

orbit drawing, star field simulation, the rendering of rocket flame and radar wave,for example. Please refer to [6] for more details about OpenGL. The CVpOpenGL

class functions are called via channel callback function mechanism, so these in-

class functions of the CVpOpenGL class must subscribe to the channel events

first.

The CVpApp class is derived from vpApp---the Vega Prime core class. Besides

aggregating the controlling classes and the CVpOpenGL class mentioned above,

the CVpApp class calls the in-class functions of these aggregated classes to

accomplish the rendering of all of the scenes, and the detailed works include the

configuration of the 3D scenes, adding subscribers to channel events, the control

of the object movement, updating the frames and so on.

The 3D model database used in the scenes is established by applying the

three-dimensional modeling software MultiGen Creator, and the model is formed

by multiple tiny triangles.


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IV. SIMULATION INSTANCE AND EFFECTAccording to the designing and realizing methods discussed above, using

Visual C++ and Windows XP as the software developing platform, based on

Vega Prime and OpenGL, the satellite navigation simulation system visualization

software are developed. The running result of the software is shown in Fig. 9. Fig.

9(a), (b) and (c) are the program running screenshots of the system information

display program, the 2D display program and the 3D display program,

respectively.


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V. RESULTSAim the visualization of the satellite navigation simulation system, the

structure of a distributed satellite navigation simulation system composed of

multi-platform subsystems was analyzed. Then associating the techniques of

visual simulation with the techniques of satellite navigation, designed the satellite

navigation simulation system visualization software, and discussed the

developing technique as well as the realizing methods.

Based on the scheme and techniques mentioned above, the satellite

navigation simulation system visualization software has been realized, and it has

spectacular visual effect. After simulation verification, it is proved that the

visualization scheme of the software stated above is feasible. Nowadays, the

software has already been employed in engineering area, and facilitates the

design and analysis of the aerospace system. Besides, the above-mentioned

designing and realizing methods as well as the applied techniques are useful for

developing the similar systems.


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(a) (b)

(c)

Figure 9. Visualization softwares' display effects: (a) the running effect of the system

information display program. (b) The running effect of the 2D display program. (c) Therunning effect of the 3D display program.


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[2] J.-Y. Zhou, Y.-F. Wang, and R.-B. Luo, "Design and Realization of Missile Attack andDefense Visual Simulation System," Journal of System Simulation vol. 21, no. 18, pp.5779-5782, Sep., 2009.

[3] F.-L. Xia, Y.-S. Zhao, "Space Mission Simulation System Based on HLA," Journal ofSystem Simulation vol. 19, no. 24, pp. 5710-5714, Dec., 2007.

[4] E.-D. Kaplan, C.-J. Hegarty, Understanding GPS: Principles and Applications,Second Edition, Beijing: Publishing House of Electronics Industry, 2007, in Chinese.

[5] G. Shepherd, D. Kruglinski, Programming with Microsoft Visual C++.NET, SixthEdition (Core Reference), Beijing: Tsinghua University Press, 2004, in Chinese.

[6] R.-S. Wright, B. Lipchak, N. Haemel, OpenGL superbible: comprehensive tutorialand reference, Fourth Edition, Boston, MA:Addison Wesley, 2007.

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