Orbit Visualization Tool (2nd generation),  Copyright © 2000 by the OVT Team.

User Guide

(Version 1.0, June 15,  2000, prepared by K. Stasiewicz)


Contents:

What is OVT-2?

The Orbit Visualization Tool is computer software that makes it possible to show satellite orbits in the Earth's magnetospheric field. The program can display satellite orbits in five coordinate systems (GEI,GEO,GSM,SMC,GSE), satellite footprints projected on the Earth's surface and shown in either geographic (GEO) or geomagnetic (SMC) coordinates. In addition to satellite orbits the software computes and displays various models of magnetospheric structures, magnetopause, and the bow shock for specified time, geomagnetic activity, and interplanetary field conditions. The models are time-dependent through user-editable activity files which control models structure and properties. The program can be used to plan operations or interpret measurements from scientific satellites,  to prepare  ground-based satellite coordination, or as educational tool in astronomy and geophysics.

Operating system and graphics

The OVT software can be installed on any Unix based machine, or on a PC computer under Windows 95, 98, or NT. The graphics used in this program is based on a higher level Visualization Toolkit (VTK), which is build on OpenGL, and Java. Thus, to run the OVT one has to install certain libraries which are distributed free of charge by the Kitware (VTK), and the Sun corporation (Java). The second generation OVT is re-written in object oriented programming language Java and it implements event handlers which propagate time/coordinate/parameters changes to all affected actors on the graphical scene. The graphics is mouse maneuverable: left mouse button to rotate the picture and right mouse button to zoom in and out.

Coordinate systems

The graphics window shows objects in one of five geocentric Cartesian coordinates described below. Let us denote the unit vector toward the Sun by S and the unit vector along the magnetic dipole axis by D (positive northward).
GEI: Geocentric Equatorial Inertial with the X-axis pointing toward the first point of Aries (the position of Sun at vernal equinox). The Z-axis points toward geographic north.
GEO: geographic coordinates have the Z-axis along the geographic north pole and the X-axis in the equatorial plane at the Greenwich meridian (longitude=0).
GSM: Geocentric Solar Magnetospheric coordinates have the X-axis pointing toward the Sun, and the Y-axis perpendicular to the Earth magnetic dipole and the Sun direction (Y=DxX).
SMC: Solar Magnetic Coordinates have Z=D and Y=ZxS. The difference between GSM and SMC is rotation around the common Y axis by the dipole tilt angle.
GSE: Geocentric Solar Ecliptic. The X-axis points toward the Sun and the Z-axis points toward the ecliptic north.
In all coordinates the third axis, not mentioned above, completes the right handed Cartesian triad (X,Y,Z).

The footprint projections on the Earth are shown at an altitude of 100 km above the average sphere of 6373.2 km in two coordinates system: geographic GEO (longitude and latitude), and magnetic SMC (magnetic local time and magnetic latitude). Field line tracing is done with the selected magnetospheric model (internal + external). Please note that in SMC coordinates  footprints are shown as MLT (magnetic local time) and MLAT (magnetic latitude) that are equivalent to dipole geomagnetic coordinates. The corrected geomagnetic coordinates are not used for display purposes because they do not represent an orthogonal transformation and therefore cannot be included in the global coordinate transformation matrices.

Magnetic models

The magnetic models include standard internal field model IGRF 1950-2000 and Tsyganenko models of the external magnetospheric field: T87, T89, and T96. The bow shock model is according to Farris et al, GRL, v. 18, p.1821, 1991, and Cairns et al., JGR, v.100, p.47,  1995. The magnetopause model is according to Shue et al., JGR, v. 103, p. 17691, 1998. All these model implementations have user-editable time-dependent property files.

Satellite orbits and attitude

The orbital programs include a standard ESOC program for computing Cluster position. Other satellites included in the distributions (Polar, Interball, Fast, Freja, Astrid-2) use standard NORAD two-line elements and SGP4 orbit propagator. The satellite menu is constructed automatically from the configuration file (sats.conf) which looks like:

OrbitDirectory=odata
# Sats
#Cluster Sats
Cluster1.OrbitFile=cluster1.cl
Cluster2.OrbitFile=cluster2.cl
Cluster3.OrbitFile=cluster3.cl
Cluster4.OrbitFile=cluster4.cl
# Other Sats
Polar.OrbitFile=Polar.tle
InterballAuroral.OrbitFile=IBaurora.tle
InterballTail.OrbitFile=IBtail.tle
Fast.OrbitFile=Fast.tle
Freja.OrbitFile=freja.tle
Astrid.OrbitFile=astrid.tle

Addition/deletion of a record in the configuration file would create/delete a satellite from the main actors menu.
If a spin data file (e.g Freja.spin) is present in the OrbitDirectory, then this information is used to compute orientation of the spin axis in respect to the magnetic field, velocity vector, and the sun direction. The .spin files must be in the format required for CLUSTER project, i.e.

1 P 1994-09-01T00:00:00Z 1994-09-07T12:30:00Z 341.00 77.00 14.000000 333.800 776.1 0.0 0.0 0.00 0.00 1994-09-01T01:10:00Z

User Interface

User interface consists of one graphics window integrated with a control panel. Objects in the graphics window are mouse maneuverable: use left button to rotate the picture and right button to zoom in and out. The middle button on Unix systems can be used to change the focus of the viewing scene.

 

Actors and Scene



The picture shows orbit of the POLAR satellite in GEI coordinates, current satellite position at time 2000-01-01T00:00:00Z and the magnetic field line passing through the satellite at this position. The footprints are shown in GEO coordinates.

The left-side panel shows list of actors that can be displayed on the right-hand side scene. Each actor has some editable properties and can be shown/hidden on the scene. This popup menu is activated with right-side mouse button, after a selection click with left-side button.

 

The bow shock and the magnetopause

The bow shock and the magnetopause have editable properties that control their shape and positions. SWP is the solar wind pressure (nPa) and IMF stands for Interplanetary Magnetic Field. The checked MP clipping means that the terrestrial magnetic field lines are not allowed to go outside the MP surface (more than 0.5 Re).

 

Magnetic Models

Magnetic models are controlled by the property editor shown in the left. Each model has an associated set of parameters which can be edited by the user. At present we have three version of the Tsyganenko models, which can be combined with IGRF or dipole internal field models.

Magnetic activity data editor makes it possible to create a time dependent activity file which is used for magnetic model determination and field line tracing. The current model settings are computed with interpolated parameters from the data file.

 

Magnetospheric structure

Magnetospheric structure represents a shell of outermost field-lines which are determined from current model parameters. If MP clipping is set in the Magnetopause property editor, then the field lines are not permitted to extend outside the MP model. If the MP clipping is off, then the field-lines derived from the magnetospheric model can extend significantly beyond the MP model. However in such a case their footprint is very narrow and corresponds to the topological magnetic cusp (for models T87, T89).

 

Time Control

The time setting (left) is self-explanatory. The maximum time step is 60 min, and the stop time must imply number of steps not exceeding 200. The satellite menu (see e.g. Actors and Scene above) is shown in italic  in case when there is no orbit elements data for the time specified.

 

Orbit Monitor

Orbit monitor is activated when show satellite sub-menu is selected. It shows the satellite position (current coordinates and time), velocity and footprint coordinates. The footprints are shown for both hemispheres, if exist. In addition, the orbit monitor shows the estimated radial distance to the current model of the magnetopause and the angle of the satellite spin axes with respect to the magnetic field vector, satellite velocity, and the sun direction. The later data require presence of the spin axis attitude file in the ODATA directory. The spin attitude file has suffix .spin and must be in the format required by the CLUSTER project. The .spin files included in the distribution contain artificial data for demonstration purposes. They should be removed or replaced by real data.

 

Dumping of orbit data

Under satellite popup menu one can select dump data, which activates the dialog shown in the left hand side. This will dump the data contained in the orbit monitor to a selected file in ovt/userdata directory. The dumping can be done manually; step by step or by cartoon mode, for the whole time interval. In the manual mode logging to the dump file occurs only when the logg button is pressed.

 

Footprints

The picture shows footprint of CLUSTER1 over northern polar regions expected for date 2001-01-01. The tic marks are every 50 minutes. The Z-axis is in GSM coordinates. Footprints can be shown either in GEO or in SMC coordinates.

 

CLUSTER configuration

Zooming at the CLUSTER spacecraft shows the spacecraft trajectories (red) and the threading field-lines (green). The satellites are depicted as balls or as arrowheads, depending on the absence or presence of the spin attitude files. In the later case, the arrow shows the actual orientation of the spin axis. The color markup corresponds to the satellite name: C1 (red), C2 (green), C3 (yellow), C4 (magneta). The observed bending of the field lines is a graphical display step problem. The actual field-line tracing is done with high accuracy.

 

The CLUSTER configuration window shows configuration parameters of the four spacecraft.
XYZ box shows the minimum box size in current coordinates that will confine all four spacecraft.
Ellipsoid shows three axes of an ellipsoid that will confine all spacecraft.
FAC box shows a box in local field-aligned coordinates around the gravity centre that will confine four spacecraft: dB-along the field-lines, dA-in the azimuthal (LT) direction, and dR-in the dBxdA, pseudo-radial direction. The configuration parameters are automatically saved in file ovt/userdata/clusters.conf.

 

Miscellaneous

Buttons Save/Export image and Print are duplicated in the file menu. When printing or saving image make sure that the graphics is not covered by other window. The resolution of the hard copy corresponds to the resolution of screen objects. The print option does not work properly under Windows 98. One can export image to a file and print or edit it with another program.

The graphics window is mouse resizable under Unix and NT systems. This does not work properly under Windows 98 and the window size can be modified only through a special file/setting window (see left). The new settings will be valid for the next OVT session.


Time advance arrows < and > change time by one step within the requested interval. Double arrows << and >> move to the start or end points, respectively.

The Earth can be shown either as continents, or as geographic/polar grid.
The axis XYZ can be hidden/shown and refer to the current selection of space coordinates.
Frame grid in three space planes can be also shown in the picture.

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