bugs

卫星仿真软件 卫星仿真软件 卫星仿真软件

desired? Probably a lot.

Opening the coverage window when animating means that the coverage
playbar is not immediately updated with playbar status, and
playbars only sync when the next playbar button is pressed.



f. FISHEYE VIEW IMPROVEMENTS

Under Insight Tk running under Cygwin, SaVi spawns a window native
to Windows. However, the fisheye view relies on X, and opening the
fisheye view would crash SaVi. Tcl/Tk can be compiled, or the xtcltk
package used, so that SaVi lives in the X window with Geomview.
With -no-X and detection we decide that the Tk window is not in an X
display and disable the fisheye menu option as a short-term option.

As a longer-term effort replacing this undesirable -no-X option,
we need to rewrite the fisheye to depend on pure Tk rather
than on Tk and X, or at least make the fisheye and X dependency a
compile-time option. (This problem may also affect building SaVi with
native Cocoa or similar Tk under Mac OS X, but that has not yet been
tried.)

Open fisheye does not update automatically when new constellation is
loaded in.

Mask elevation/satellite cone selection in coverage does not update
the fisheye mask circle. If satellite cone is selected, could disable
green mask circle and use of mask option.
(COVERAGE_ANGLE_TYPE is unused in C.)

Provide dropdown menu of large cities that sets latitude and
longitude for the ground terminal.

Now that the fisheye window is resizable, having controls partially
obscured at small sizes is messy. Can this be improved? Not resizing
the window when recording tracks is a deliberate choice, given the
complexity of the alternative.

Add slider to select size of fisheye crosshairs; will need to adjust
text positioning slightly. Can we add this on buttonbar?

How much work would be required to enable multiple fisheye windows
to be spawned? Probably a lot, if pass times are to be recorded in the
SL list structures on a per-view basis.



g. GEOMVIEW INTERACTION

Under Cygwin, the large list structures used in writing footprints and
cones cause complaints about not being able to seek back far enough in
pipe. This appears to relate to how piping is handled under Windows;
an alternative to the oogl used in:
footprints.c::write_footprints_geom()
cones.c::write_cones_geom()
would be good to have. Footprints and cones are off by default to
avoid this problem.

Geomview binary format is only used in one place at present (the
default satellite marker if the architecture permits it), but
offers a scaling advantage. Note that e.g. Geomview 1.8.0 (Linux,
some glibc) has problems with handling binary format; selecting
a more complicated marker type than the default green dot avoids
use of binary format entirely, but an explicit option would be
better.

Rotation of satellite markers as they approach the poles is inaccurate;
detailed satellite solar panels should be at right angles to the ecliptic
and rotate to follow the sun (if there's a sun...), rather than pointing
east-west, in order to get maximum sunlight. That's reality; for
visualization, having panels at right angles to the planes
increases visibility - when the planes are drawn.
Could use inclination of orbit.

Make this unwieldy SaVi/Geomview combination run in root window under
Xscreensaver, in long tradition of overdone OpenGL hacks. To do that,
more command switches (script filename, at least) must be passed to
SaVi through Geomview.

Can central blue sphere rendering be rotated so that lat/long
lines map to barely-visible rendering of sphere segments?
Can we draw latitude/longitude lines that rotate with the
central body as an option? This would be like Geomview's
'Draw Unit Sphere Projection' Camera menu option, but rotating
with the Earth.

Replace equatorial plane with more detailed sectored concentric
circles.

Can Geomview postscript output be improved and made useful by
tweaking SaVi's oogl? This probably requires work on Geomview.

Translucent surfaces (e.g. yellow selection cubes) may not
be that visible in some renderers.

Cone segment rendering can be smoothed by issuing the command:
(merge-baseap appearance { shading smooth })
to Geomview. This could be made an option in the rendering menu.

Add a 'Sky view' rendering option that combines the following:
  - switches Geomview to spherical geometry, so we're looking
    out from the centre of the Earth;
  - turns off central body, so that we look through outline
    continents.
  - turns on footprints, turns off spotbeams.



h. DYNAMIC TEXTUREMAPPING WITH GEOMVIEW

Dynamic texturemapping is described in the file
README-COVERAGE-TEXTUREMAP
which can be found in the same directory as this README file.

Dynamic satellite coverage passing over the poles shows an interesting
'circle' effect where coverage diversity appears to be evaluated once
for the entire around-the-pole circular region. Look into this.

When detail Earth is turned off and Geomview is drawing a simple blue
sphere, we could choose to show coverage sans map via a texturemapped
sphere sans Earth map.



i. VARIOUS

Improve time display, so that groundtrack drawing has useful
'elapsed time', and the time that the fisheye and coverage
displays are stopped can be easily read from their respective
windows. Average coverage display needs to count number of intervals
sampled, since time between intervals can be changed.

Allow switching between a set of default values for various planets
(e.g. Venus, Earth, Mars) with matching surface maps, and even a default
Constellations menu for each planet. Accurate gravitational models for
each planet would be useful.

Makefiles, header files and #include dependencies could be much better.
There's little attempt to optimise with judicious use of inlines,
but since we spend most of our time in the Tcl interpreter, gains
could be minimal. Adding -O2 in src/Makefile (and turning off -g debug)
has produced a smaller and faster executable.



j. INTERACTION WITH OTHER 3D RENDERERS

Are there other 3D renderers with piped input for which SaVi could
add support?



k. INTERACTION WITH OTHER SIMULATORS

network simulator ns - http://www.isi.edu/nsnam/

SaVi could generate output in a format suitable for Lloyd Wood's perl
ns satplotscripts. This really requires working intersatellite-link
functionality to be useful; satellite positions alone doesn't give
much unless you need a postscript map.

ns could write the simplest SaVi format that describes satellites
(the simple Tcl scripts that SaVi saves files as...) to allow SaVi
to show where ns satellites are. Over time the ns and SaVi simulations
will diverge, since SaVi has the more complex orbital model -
a simple model could be made an option in SaVi.

As of ns 2.1b8, the default ns output format for Lloyd Wood's perl ns
satplotscripts describes long/lat position, but does not include
orbital information such as altitude, making it useless for SaVi as
it stands. A new format is needed.



3. REMAINING INTEGRATION WORK FROM UNRELEASED SAVI 1.1
======================================================

This work requires detailed knowledge of relevant geometry,
satellite requirements, SaVi and Geomview in order to build on
Patrick Worfolk's efforts.

- Intersatellite link simulation in SaVi and Geomview - although
  this really needs a good scripting interface, and must also
  consider visibility, handoff, and configuration.

- Sunlight simulation for Geomview. An accurate terminator a la
  the coverage-panel-like sunclock would be nice; the sun can be
  thought of as a very distant satellite in an orbit inc 23.5 deg
  from an Earth-fixed frame of reference, and this has been
  simulated with a simple Tcl script. Problems with Geomview's
  lighting remaining consistent when the Earth is rotated in
  Geomview have prevented this being added to SaVi.
  (use of merge-ap instead of merge-baseap may be related here.)



4. THE ORIGINAL SAVI 1.0 WISHLIST
=================================

- A user manual!

- Ability to input satellite positions correctly in two-line-element
  format, allowing multiple satellites with different epoch
  times to be simulated correctly simultaneously.

- Incorporation of actual time into program so that the evolution
  of real satellites can be monitored.

- Ability to change lighting in 3D view to visualize night and day
  on the Earth and dynamic evolution of the sunlight.
  (This has been prototyped in Patrick Worfolk's unreleased SaVi 1.1.)

- Full incorporation of NORAD SGP4/SDP4 propagation models for
  NORAD two-line element sets for added realism.

- Additional map projections for the coverage display.
  (An unprojected map has since been added as of SaVi 1.2.2.)


Lloyd Wood <[e-mail]>