BUGS recognized in SaVi ======================= $Id: BUGS 148 2020-01-18 02:50:25Z lloydwood $ This list of BUGS describes caveats and problems with use of the SaVi satellite visualization software. This document contains the following sections: 1. Caveats in use of SaVi. Be aware of these. 2. Platform-specific issues. a. Mac OS X i. Mac compilation hints -- for SaVi -- for Geomview ii. 10.5 (Leopard)-specific issues -- for SaVi -- for Geomview iii. Other minor Mac-specific issues -- for SaVi -- for Geomview b. Cygwin on Microsoft Windows -- for SaVi -- for Geomview 3. A detailed SaVi wishlist. Notes on issues in these SaVi releases. a. Coding and build issues b. Scalability c. Scriptability d. User interface e. Coverage view improvements f. Fisheye view improvements g. Geomview interaction h. Dynamic texturemapping with Geomview i. Various j. Interaction with other 3D renderers k. Interaction with the network simulator ns l. Desirable constellations to simulate 4. Remaining integration work from unreleased SaVi 1.1. 5. Remaining items from the original SaVi 1.0 wishlist. 1. CAVEATS IN USE OF SAVI ========================= Changing default simulation parameters (central body radius, gravity, etc.) can cause unexpected behaviour; scripts generally describe satellites in circular orbits via an altitude above the body's surface. Use at own risk. If simulating a different planet to Earth, we should force the -orbit-model J0 flag to avoid simulating Earth's oblateness and environment. J0/J2 should be selectable in the params dialog. Any changes should reset time to zero - with a warning. Two-line-element (TLE or 'elset') reading and constellation code in tcl/constellations.tcl still needs considerable work. Reading .tle files is experimental. This is not guaranteed for multiple satellites of different epochs, so you can't really just expect to download a .tle file, load it in and go. Improving this and introducing clock time would make SaVi far more practical. (Sidereal time and the Earth's motion around the sun is not simulated; noted by Tom Tessier.) Selection: selected satellite is not visible as selected in Geomview until a marker type is first selected or satellite orbital elements are edited. Operations on multiple satellites (e.g. Cut) only work on the last satellite selected. Sunlight is approximated by having the sun orbit the Earth as a distant satellite with the appropriate year-long period. This should not be done as a J2 calculation, but should at least be J0. Geomview's lighting rendering needs to be fixed to match this coverage footprint. 2. PLATFORM-SPECIFIC ISSUES =========================== a. MAC OS X i. Mac compilation hints -- for SaVi SaVi and Geomview need Xcode (included in Developer Tools with the Mac OS X system installer copy, or downloadable from Apple) to provide the tools that can compile these and other programs. As of Mac OS X 10.7, Xcode is now an app available from the Mac App Store. As well as downloading and installing the Xcode app, it may be necessary to explicitly enable command-line tools so that e.g. gcc is available. The command line tools must be selected in: Xcode > Preferences > Downloads > Components > Command Line Tools Simply typing 'make' in a Terminal window may generate a dialog to install the app and necessary command-line tools. Alternatively, the command-line tools can be installed by typing: xcode-select --install Although recent releases of Mac OS X include Tcl/Tk headers, they do not include the X11 headers that Tk needs to compile. One way to get these headers is to install the XQuartz package from http://www.xquartz.org/ The XQuartz copies of X11 headers are looked for during compilation. The Tcl/Tk libraries shipped with Mac OS X releases have some user-interface problems and are prone to crashing. It is preferable to install a later ActiveTcl release from http://www.activestate.com/activetcl and then choose to build with that instead; to do so, uncomment the second, commented, TCL_LIBS = line in src/Makefile_defs_macosx before compiling savi by typing make ARCH=macosx Mac Tcl issues fixed in ActiveTcl include: - Mac OS X 10.5 Leopard menu problems - accelerator key crashes - coverage panel angle slider crashing Tcl due to a busy event loop when texturemapping, cone and footprint drawing are on. -- for Geomview On Mac OS X 10.8 or later, you will need to install XQuartz from http://www.xquartz.org/ to provide an X11 environment. To build Geomview on Mac OS X, you must first install a Motif clone such as Lesstif (available via www.geomview.org's Downloads section). In Lesstif's directory you will need to configure make sudo make install and okay the sudo with a password to place Motif files where Geomview expects to find them. Geomview works well with OpenGL, but the OpenGL header files needed are not included in Xcode by default. They were an extra optional package provided with the Mac OS X system installer. Building Geomview with ./configure --without-opengl make is a fast way to get started, but the OpenGL rendering is recommended for coverage texturemapping. To build Geomview with OpenGL once these optional header files are installed: ./configure --with-opengl=/usr/X11R6 make and then optionally to make Geomview available from the command line everywhere: sudo make install ii. 10.5 (Leopard)-specific issues -- for SaVi The Tk 8.4.7 supplied with Mac OS X 10.5 (Leopard) has problems displaying SaVi's menubar. To work around this, menu buttons can be put in each SaVi window with: savi -redrawn-menus This is not required on Mac OS X 10.6 (Snow Leopard) or 10.4 (Tiger), where the Mac menubar can be used correctly. The ./savi launch script attempts to detect 10.5, and adds the -redrawn-menus flag to make SaVi usable for Leopard users. This avoids having to add the parameter at the command line each time SaVi is launched. Installing ActiveTcl, uncommenting the TCL_LIBS line before compiling, as described above, and removing the -redrawn-menus flag from the ./savi launch script is the preferred way to work around the user interface problems of the Tk supplied with 10.5. -- for Geomview If doing make of Geomview fails to link at end with a 'cycle in dylib re-exports with /usr/X11/lib/libGL.dylib' error, use the following single-line, no-breaks command: export LDFLAGS="-Wl,-dylib_file,/System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL.dylib:,/System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL.dylib" then repeat the previous instructions. This problem is caused by a linking bug in Leopard. iii. Other minor Mac-specific issues -- for SaVi - Menu shortcuts are disabled on the Mac unless -redrawn-menus is used. This is to prevent a freeze on using a keypress to open a window (seen in 10.6 with Tk 8.5.7). 10.7 is unaffected, and shortcuts can be enabled for ActiveTcl by editing disable_mac in tcl/utils.tcl. - On compilation, two binaries are produced: bin/SaVi-macosx.bin and bin/SaVi. You can rm bin/SaVi-macosx.bin to get just 'SaVi' in the menubar as the application name. - Under the Tcl/Tk supplied with 10.5, coverage colour buttons are only fully coloured when another application is frontmost. - Under the Tcl/Tk supplied with 10.6, menu highlight colours are incorrect; highlighted text remains black. -- for Geomview - With X11 rendering, Geomview does not appear to be able to control its background colour, which is always grey. OpenGL rendering is fine. b. CYGWIN ON MICROSOFT WINDOWS SaVi and Geomview can be installed as packages by the Cygwin installer. 32-bit Cygwin and the newer 64-bit Cygwin can coexist on a Windows PC. 32-bit Cygwin has often had better Geomview interaction in the past, and so was preferable for SaVi. If both 32-bit and 64-bit Cygwin are installed: - Depending on which XWin the Start menu Cygwin-X folder launches, the other can be launched when that is not running by launching the appropriate terminal, then typing startx -- -multiwindow -clipboard & - The Task Manager will indicate whether 32-bit or 64-bit Xwin.exe is running. - uname -a in a terminal indicates whether that terminal is 32-bit or 64-bit; x86_64 is 64-bit. -- for SaVi When expanding the coverage window to show a tiled coverage map, there can be two lines of pixels, one to the left of the map, one to the right, where coverage is not drawn on the background. Satellites and maps are drawn correctly. Oddly, this only appears under the 32-bit Cygwin, not in the newer 64-bit Cygwin. This has not been seen on any platform other than 32-bit Cygwin. Cygwin support isn't seamless, and may need some editing of tcl/Makefile to support the version of Tcl Cygwin uses. This caveat only appears to apply to very old versions of Cygwin; not Cygwin 1.5.6-1 and later. Under cygwin, specifying -mno-cygwin to gcc in src/Makefile in order to build using MinGW generates errors. We're a long way from a standalone Windows executable. -- for Geomview SaVi and Geomview can be installed as packages by the Cygwin installer. The SaVi/Geomview combination took a while to become functional under the new 64-bit Cygwin introduced in March 2013, with OpenGL and piping problems. Under 64-bit Cygwin, you can try building Geomview with: MOTIFLIBS='-lDtPrint -lMrm -lXm -lXt -lXmu -lXp -lXext -lX11 -lSM -lICE' ./configure --with-motif=/usr --with-opengl=/usr CPPFLAGS="-DglBindTextureEXT=glBindTexture -DglDeleteTexturesEXT=glDeleteTextures" make 3. A DETAILED SAVI WISHLIST =========================== This is an additional wishlist of improvements for SaVi originally accumulated during work for the SaVi 1.2 release during October-November 2001, and kept up-to-date with later development. Development takes place at: http://savi.sourceforge.net/develop/ Many suggestions (such as the user interface and fisheye modifications) should be straightforward if you have some Tcl/Tk/C experience and the spare time and interest. Others are difficult. a. CODING AND BUILD ISSUES - make install is needed. That should probably match the current debian package. Early creation of it may have been able to prevent the previous package problems caused by maintainers unfamiliar with the savi tree, described below. - Binary packages are not created by the SaVi authors. You can always download SaVi from http://savi.sf.net/ and compile it to get all the files created for SaVi. - The savi-1.4.3 package available from getdeb.net from December 2009 onward (and available in Ubuntu's Synaptic package manager) initially removed the textfiles and manual from SaVi. This package installed SaVi under /usr/share/savi, while the COPYRIGHT file was edited, renamed 'copyright' and placed under /usr/share/doc/savi. This broke SaVi's help system by removing all help information. Packaging was fixed in later revisions. These packages were not initially compiled using zlib, although and making zlib a package dependency is straightforward. More details are in the PACKAGING textfile. - $HOST or $HOSTNAME? One or both have the machine info we need for the compile version info preserved in Help/About... - gv_utils.c warning: implicit declaration of functions fileno and fdopen because they're POSIX, not ANSI C, even though they're normally in stdio.h; could set -std=gnu99 flag to relax restriction if this mattered. - The executable bin/SaVi (named for viewing the process name, e.g. in the Mac OS X menubar) is considered the same name as the savi script on case-insensitive file systems (Mac OS X, Windows). This may lead to confusion, particularly if src/Makefile is ever made to build in the savi directory. - Improve open/close filehandling and catch errors. - Under error catching, if SaVi is launched from a terminal window and backgrounded with the & metacharacter, and that terminal window is then closed, writing status messages to stderr, e.g. when loading a new constellation, fails due to a broken pipe. The resulting Tk error dialog stalls SaVi until it is closed. Option to remove ALL output sent to stdout? -quiet? Would need printf varargs wrapper. Could log to file or to a Tk log window instead - but little point sans timestamps? - We should really be using snprintf instead of sprintf. - We should examine jerkiness when used with Geomview, particularly under Cygwin. utils.c::millisleep() calls select() without reference to the state of the pipe to Geomview; how can this be made smarter? Should we sleep after gv_end()/gv_stop() ceases nesting? - Command line handling to note what options are set should note more for hint in About dialog. For debugging purposes, could allow override of existing global variables by writing support for -tclvar -tclvar by setting them near the end of init.tcl init code. Check existence of value set and warn if not already present. - Menu shortcuts don't work while any menu is dropped down. This looks like a Tcl failing crossplatform. - -fisheye and -coverage flags to spawn those windows at startup? How do we set size? -large-map/-snmall-map and -levels handles that... -camera to spawn n geomview cameras at startup? 2nd/3rd could be north/south pole views. How to position windows on screen? - Rewrite README (for building SaVi) and README-TEXTUREMAPPING into README (for building), SAVI-USE, and GEOMVIEW-USE for better online help. - Filehandling: why does the SaVi package installed as a deb say 'File not found' when a file parameter is passed? b. SCALABILITY - Scaling up. Can SaVi detect available CPU power and e.g. scale number of segments in drawn orbit circles/number of sides to a coverage cone appropriately for Geomview? A slider or command switch giving some control over this would be very useful. Scaling up the number of segments when drawing highly-elliptical orbits has been done, but ORBIT_SEGMENTS defined in include/constants.h needs to be passed to Tcl as a variable. More use of Geomview binary format (discussed below) may help. - Scaling down. Geomview rendering is optional; you can conserve CPU by running SaVi standalone. SaVi 1.2 and later don't do Geomview calculations when run standalone, although 1.0 did. Why shouldn't Tk and a graphical display also be optional? You do need a Tcl parser - that's essential - but we can execute scripts to build satellites and get results; we can make use of command-line switches, and we can pipe graphics to stdout for a variety of uses, including building web cgis (a la Chris Meenan's footprint generator). c. SCRIPTABILITY As well as scripts that get results there needs to be a scriptable interface to record tracefiles. Scriptable recording of satellite-related values over time periods would be very useful; the self-scheduling Tcl procedure model that is used in the network simulator ns-2 (see below) may be worth emulating. Having Tcl/C interaction daisy-chained as keywords off the 'satellites' keyword is awkward, particularly for Geomview interaction, where a 'geomview' keyword would seem more intuitive. Perhaps a 'C' keyword? d. USER INTERFACE A user manual has been written and placed in the manual/ directory, but more detail is needed. The manual is not yet directly accessible from SaVi; could SaVi find and spawn a web browser? Building a web browser into SaVi seems a bit much. The Tk procedures in tcl/tcl_utils.tcl (inherited from dsTool) are straightforward to use, but are not that efficient in using screen real estate. This makes SaVi cluttered, even on a 1024x768 display. SaVi 1.2 has improved things, but this still needs more work. * Main panel: A realtime push-hold button next to Time Interval would be useful; removes Rendering menu (->Geomview menu) when Geomview is not present. Move current time into reworked playbar line instead? Cutting to remove a satellite jumps to end of (long) list, unless start of list is shown. Bindings are needed for cursor up/down so that satellite selection moves. * Coverage panel: Some wasted space here. When -large-map is selected the playbar at end is drawn below the bottom of a 1024x768 screen, which is a problem if you can't move windows from available edges - which is why the buttons are also listed as commands in a menu. Reaching the coverage angle options also becomes tricky. Clicking and dragging the map sideways to shift the view would be cool - esa's Space Trajectory Analysis v3.0 does this. Bindings are needed for cursor left/right (forwards/back) and shift-cursor left-right (single step forwards/back) * Edit satellite: Dialog layout can be improved, with better alignment of captions, text boxes and sliders. Apply button was removed since values do update live - but does that also hold for older versions of Tcl? There's no easy way to select multiple satellites so that you can change a checkbox setting for all of them. Panel can be left open when inappropriate, e.g. when a new constellation is loaded in. Should switch to editing a new satellite. * Rosette and crude star generators: Dialog layout can be improved, with better alignment of captions, text boxes and sliders. Slider positions do not update to match text value changes. Create overriding 'Show all {satellites | orbits | coverage }' checkboxes that, when checked, force related checkbox (in satellite Edit parameters) on and the feature visible for all satellites. When checked off, disable the feature for all satellites. These would be entries on the Rendering menu, under 'Real-time mode'. Provide menu of colour choices for pane backgrounds, highlights etc. It's possible to type into the help menu text windows. That should be prevented. But that is not simple in Tk: http://wiki.tcl.tk/1152 Ballard/crude star generators need to create info text in "About constellation" window. Look at how the initial LEO satellite text is created. Need to create info text separately from function that we may in future call from scripts that we collapsse down to Ballard? e. COVERAGE VIEW IMPROVEMENTS Now that we have satellite names, an option to show them in the coverage view would be useful. The satellite plot scripts do this for print via xfig. Could blend coverage maps somehow with the detailed map, but that means uncompressing it and blending on a pixel-by-pixel basis, or setting alpha transparency in Geomview for a coverage sphere over the earth sphere. Decay/sunlight options are really mutually exclusive, and could be done via a popup menu: No coverage (all-white background) Coverage (white background) Coverage and decay (default) Coverage and sunlight (two shades of decay) Coverage over land and sea (blue background) but we need masking for all supported projections first. Drawing the Earth map last in each rastering is nice for sending to Geomview earlier, where the vector Earth can be overlaid instead - but means that green satellite cross markers are behind and occluded by continent/country outlines. Ideally we have subsatellite nadir markers drawn by Geomview, with bitmap crosses drawn after the bitmap Earth maps, and not sent to Geomview either. Could fix coverage satellites drawn behind map bitmap outline problem. In map-drawing section, test value in lookup table, i.e. that it's not green, before plotting. Or could move loop of detect-and-draw-green-crosses after map drawing loop, at cost of not drawing them in Geomview. If "use sunlight" is on, why is change shading only restricted to land/satellite coverage only? For land/sea both should change; debatable for others. But labels need to update to show 1/2 sats etc. Could implement 0 satellites in view/0 intervals as two white boxes, not given in color swaths, but colors set individually by clicking buttons. Possibly better as menu option spawning color box? Set uncovered map color? Should intervals off default to 4+ colors, not 1? Add greyscale option for colors? diversity is white? Unless land/sea? As well as allowing coverage angles to be set per satellite, having multiple fooprints per satellite at set elevation angles (5 degrees, 10 degrees) would be very useful. Either approach could be used to build traditional geostationary iso-coverage maps, marked out with diversity colours. What is the diversity/decay value of the pixel that we have clicked? Report it next to fisheye lat/long coords. Unlike coords, this would need to be updated in real time. If fisheye is open, then we likely already know it from within the red circle, and can just repeat it in coverage? Useful reality check by comparing the two. Should opening coverage panel turn on vector Geomview map overlay? Saving maps now supports .gif, as that's integral to Tcl. Support for handling .png requires a non-buggy version of Tcl 8.6 or later, and produces larger non-indexed files, so it's not a menu option - but if .png is given in the filename, an attempt to save as .png will be made. May need to revisit filetypes here at some much later point. There are alternatives to plotting full circular footprints: - just plotting only edges of footprints - hollow circles. - plotting imaging swath widths, i.e. a line perpendicular to the orbit inclination, width diameter footprint. - plotting complex spotbeams, again aligned with respect to to the orbit inclination. (Chris Meenan's footprint generator demonstrated hexagonal arrays.) This would involve making changes to e.g. src/stats_utils.c::fill_grid() and intensity_circle_footprint() Look at masking SaVi logo onto coverage maps - this makes most sense in corners of spherical and sinusoidal maps, but area used would need to be discounted from coverage calculations. Update all Earth maps to track more recent political boundaries. A couple of pixels of west Mexican coastline are missing from the 1024 unprojected map. Consider producing better outline and landmass mask maps across all projections, and even new projections, by generating them using the d3.js map drawing functionality. Unfortunately, this means first understanding d3.js. The coverage slider position should be updated when a script loaded from the menu changes the coverage angle. Threshold altitudes for enabling coverage footprints and cones are useful for elliptical orbits where satellites only transmit at apogee, but is currently only a command-line option. This may be more useful for a mix of orbits if specified as an angle around apogee, rather than as an altitude. Similar thresholds could be implemented for latitude and longitude, based on satellite position, and implemented as command-line options to start with, or a Coverage constraints coverage panel menu option. -coverage-latitude-max, -coverage-latitude-min, -coverage-longitude-max, -coverage-longitude-min, with -coverage-altitude-max, -coverage-altitude-min renaming the transmit-altitude-max/-min already implemented to fit the set. Longitude calculation for spherical fisheye clicks are inaccurate. Edge calculation methods have visible differences (as does sinusoidal). Area calculation hasn't been attempted; calculations of areas in general for all projections are poor estimates anyway. Using sinusoidal coverage map, full coverage reads from 99.6% to 99.8% due to rounding at curved edges of map. Coverage calculations for all projections are estimates at best, reflect the map projection in use by changing with latitude, and are limited to not exceed the 100% threshold. Calculations should really reflect degree of coverage overlap and be consistent across all views. Working off stats_utils.c::footprint_circle_radius() when that is computed, not off a distorted map, can give total coverage for each small circle that coverage generates. These can be summed to give overlapping coverage. Calculating amount of coverage overlap for 1/2/3 etc. satellites is possible by counting pixels, but still depends on choice of projection and latitude of satellite. For handling overlap, see Kantsiper and Weiss, An Analytic Approach to Calculating Earth Coverage, AAS 97-620, while they were at MIT, for an analytical integration approach using the inclusion/exclusion principle. Also Brian Kantsiper, A Systematic Approach to Station-Keeping of Constellations of Satellites, PhD dissertation, MIT, Feb 1998. See also A. Gonzalez, Measurement of areas on a sphere using Fibonacci and latitude-longitude lattices, Mathematical Geosciences, January 2010, pp. 42-49. http://arxiv.org/abs/0912.4540 The correct way to count coverage overlap is debatable. Counting pixel intensities and saying X% of the earth has single satellite coverage, Y% of the earth has double coverage... could be useful - and these percentages could then be overlaid on the colour key wells. But counting pixels from a map still introduces some distortion. When choosing new colour shades after animating forwards then stopping, the satellites move on an interval unexpectedly as the map is updated with new colours. Is this due to computed coverage finally being shown by tk_update()? Project groundtracks for the next n hours only projects forwards in time, even if the simulator is currently being run backwards - is this the least confusing approach? Enter negative number to project backwards. When altering the coverage map and tiling, remember to run the Teledesic (840) simulation to check that the top and bottom of the map are visible as a single line of uncovered (blue or white) pixels in cylindrical view. Tk does require a unit offset. Add option to fade groundtracks to background over time, just as interval decay works for coverage areas. When recording groundtracks, erase the cross arms and leave only the subsatellite point. Coverage areas of the selected satellite(s) can be shown in different shades - possibly shades of green. Add optional latitude/longitude lines. Could add equator line to match showing equator in fisheye view. Earth outline on sinusoidal map is drawn using different algorithm to backdrop. Overlap is poor; both should be drawn on the cached map, rather than on each coverage map drawn. This matters less when the backdrop is set to black to match the outline. How much work would be required to enable multiple coverage windows to be spawned, so that multiple projections could be seen, and any available cylindrical or unprojected projection is used for texturemapping if 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. Menu options invoking popup windows to control project groundtrack, coverage angle slider, and minimum transmit altitude slide would be useful on small screens where these controls are offscreen at the bottom. Minimum transmit altitude is of minority interest, does not require slider to always be onscreen. f. FISHEYE VIEW IMPROVEMENTS 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 would be a deliberate choice, given the complexity of the alternative.) New cross location in coverage map is not removed immediately when checkbox is turned off. Add slider to select size of fisheye crosshairs; will need to adjust text positioning slightly. Can we add this on buttonbar? When equatorial exclusion zone is shown, satellites are not indicated as within or outside it. This needs to be figured out. Equator altitude should be figured out from first principles in case simulation constants get changed and we're not simulating Earth. We support minimum elevation of the terminal, i.e. whether the terminal can see each satellite, but do not consider half-angle of the satellite, i.e. whether each satellite can see the terminal. Considering both would be ideal, and useful as a prelude to connectivity/link work. Could create fisheye orbit markers to show trajectory of currently selected satellite, if any. Would need to be a separate satellite marker list, since parallels table wraps around. Do we space markers in RAAN or time? Would need to cut down on satellite info to just the minimum and create a special marker group, then simplify equator code to use it? Would this even make sense with HEO orbits, where markers won't be spaced evenly? Could we create markers for each satellite as lists hanging off the Satellite in the satellites list? Hard to keep updated. 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. A fisheye view that wandered (randomly?) over time would be nice to have, as it could show the equator and latitude lines moving smoothly. This would probably require a simulation event scheduler to be implemented so that commands could be executed on repeat intervals. The -debug flag outputs information about satellite positions, but it's verbose, showing angle to all satellites, even those below the horizon, and lots of debugging information for visible satellites. A decent log format for visible satellites and their angles above the horizon is needed. Saving bitmaps would be nice to have as an option. Postscript can always be converted to a bitmap via GhostScript: gs -dNOPAUSE -sDEVICE=png256 -r300x300 -sOutputFile=out.png -q -dBATCH out.ps but Ghostscript is a tad unwieldy, and since you'll end up cropping the results anyway... it's simpler to just take a screen capture. g. GEOMVIEW INTERACTION Geomview coverage cones and footprints are dynamically updated when the coverage view angle slider is moved. For cones, this is computationally laggy for large constellations. Speed it up by forcing a delay and scheduling a later update after a timer expires? We're already collapsing it in BEGIN/END. Should gv_end force a texturemap update for after e.g. loading a constellation? Should footprints be turned on if dynamic texturemapping and switching to a projection that cannot be texturemapped? Fisheye location(s) should be shown in Geomview - another colored line? Now that we have satellite names, an option to show them in Geomview would be useful. This would be even harder than showing in the coverage view - look at how The Orrery, another Geomview module, renders fonts and text. Could make markers distinguish satellites - a satellite struct field holding a number mapping to dot/sphere/box/sat or colour (since shades of black aren't useful), and text column saying marker type if geomview is running. Selecting marker could ask for all, or operate on highlighted selection of satellites. This looks hard. Look at altering sleep code to give longer sleeps when Geomview is running and animating, so that more CPU time is devoted to Geomview and overall performance is made more responsive. Being able to control and program camera position, to e.g. show exactly what a satellite sees at nadir as the satellite moves, would be very useful to have. Geomview's light source positioning appears to be buggy at present, as shown by savi -geomview -sun-lighting. Could implement a terminator plane at right angles to the sun pointer, reusing equatorial plane code. Quitting SaVi as a Geomview module can leave the blue Earth sphere behind. This was identified as a bug in Geomview exposed by chosen -O3 optimisation when building, which vanishes when -O2 is chosen - see the January 2012 geomview-users archives. Running under Geomview with -fake-geomview flag on as well leads to weird behaviour, so don't do that. One or the other! Should be able to scale one or all satellites in size. Being able to scale one spherical satellite to large could be useful for simulating the Moon. But would need to match position to J2 model. 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. (Face on to the sun at right angles to the ecliptic is at 67.5 degrees to the equator, which is 22.5 degrees to the ecliptic.) 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 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, or with a translucent circle sized to the current stationary orbit as set in parameters. Translucent surfaces (e.g. yellow selection cubes) may not be that visible in some renderers. 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. Can Geomview postscript output be improved and made useful by tweaking SaVi's oogl? This probably requires work on Geomview On Mac OS X, Geomview does not support the Mac menubar, but uses its own Motif menus in its main window. This means that switching between SaVi and Geomview is a little disruptive to the user experience. This cannot be fixed only in SaVi. Check deleting central body and turning off simple earth. only works in one order, should work in both. Loading in constellation updates texturemapped coverage slowly. Because we need to change earth types? Geomview 1.8.1 points: These are unlikely to be dealt with, as 1.8.1 no longer builds with modern compilers. With Geomview 1.8.1, the large list structures used in writing footprints and cones cause complaints about not being able to 'seek back far enough in pipe.' This is related to how piping is handled, and the piping code rewrite by Claus-Justus Heine in Geomview 1.8.2 release candidates for the 1.9 releases appears to have fixed this. An alternative to the oogl used in: footprints.c::write_footprints_geom() cones.c::write_cones_geom() would be good to have for remaining Geomview 1.8.1 users. 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. 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 BUGS 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. This may be dependent on Geomview rendering options. Coverage texturemap is not immediately updated when turning 'project groundtracks forward in time' on or off, so it is out of sync with coverage window until the next animation step. i. VARIOUS Constellation generation tools should be working at a higher level of abstraction: generating constellation to match input properties for behaviour and characteristics, rather than just taking orbital parameters as input without calculating what is needed and then generating those parameters to give a desired outcome. Implement per-satellite coverage angles, as a property of each satellite when it is created, like the name. But global coverage properties for constellations are useful, and the global slider will be hard to give up - how do we do both? Do we need to store half-angle/mask setting on a per-satellite basis? 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. Implement a -start <+/- seconds> switch, so that a simulation can be loaded at a specific point. Also -coverage, -fisheye, -edit to open up the various windows on startup; can these be scripted? 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. This wuold involve changing the body gravity/spin defaults and possibly adding a finetuned special-case per-planet orbit model to handle the equivalent of Earth's J2 precession. A different default colour scheme to indicate 'not Earth' is probably also a good idea. A number of scripts - Clarke geostationary, Draim, possibly Molnya/Tundra - could compute from the defaults and generalise to any planet; three-satellite Mars stationary would be the first target. Other constellation scripts would be Earth-specific. More accurate Earth gravitational models than J2, e.g. J20, could be implemented via the new -orbit-model flag and the switch cases in orbit_utils.c::oe_time_to_oe(). Related to that, the faked 'sun' satellite should always be running off the simplest Keplerian J0, to avoid amplifying Earth oddities. Accurate gravitational models for each planet would be useful. Maps for each planet can be obtained from e.g. Stuart Levy's The Orrery for Geomview, or from James Hastings-Trew at http://planetpixelemporium.com/ JHT's maps are unprojected, so require STSPHERE CYLINDRICAL 1 0 0 0 rather than { : numesh_h } in oogl/earth.oogl, which means at least Geomview 1.9.0 for support. They're large, even once run through jpegtopnm and compressed, so would have to be optional. A way of drawing coverage on a translucent sphere just over the planet map (but just under e.g. the Earth boundary vectors) would be useful, so that colourful maps could be combined with coverage and diversity. But this needs alpha rendering support; easier to do the maths and mapping upfront when drawing a single coverage map. TLE loading code is inelegant; a new popup function tying menu name and url to load together would be desirable and easier to maintain. Makefiles, header files and #include dependencies could be much better. There's no attempt to optimise with judicious use of inlines, but since we spend most of our time in the Tcl interpreter, gains would be minimal and we can't inline functions in other files anyway. 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? An alternative is to simply render the constellation in a web browser using d3.js. This is shown to be possible by the animations in: Ashlee Vance, The New Space Race: One Man's Mission To Build A Galactic Internet, Bloomberg News, 23 January 2015. http://www.bloomberg.com/news/features/2015-01-22/the-new-space-race-one-man-s-mission-to-build-a-galactic-internet-i58i2dp6 so scripts in Javascript would replace Tcl, and d3 driving the browser would replace Geomview. k. INTERACTION WITH OTHER SIMULATORS network simulator ns-2 - http://www.isi.edu/nsnam/ SaVi can generate output in a format suitable for Lloyd Wood's perl ns-2 satplotscripts. This really requires working intersatellite-link functionality to be useful; drawing satellite positions alone doesn't give much over the coverage panel, other than satellite names, unless you need a postscript map. ns-2 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-2 satellites are. Over time the ns-2 and SaVi simulations will diverge if SaVi is using the more complex J2 orbital model - the simpler J0 model should be preferable in this case. The default ns output format for Lloyd Wood's perl ns-2 satplotscripts describes long/lat position, but does not include orbital information such as altitude, making it useless for SaVi to simulate from files in that format as it stands. A new format would be needed. The later ns-3 does not yet include satellite simulation functionality. l. DESIRABLE CONSTELLATIONS TO SIMULATE Many newly-announced large satellite constellations can be simulated, and there's a backlog of FCC filings with technical supplements to find, read, and create outline simulations from. Add a Chinese BeiDou-2 navigation constellation simulation script. The complete perfect BeiDou-2 constellation has five geostationary, three inclined geosynchronous, and 27 medium earth orbit satellites. 4. 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. 5. REMAINING ITEMS FROM THE ORIGINAL SAVI 1.0 WISHLIST ====================================================== - 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. - Full incorporation of NORAD SGP4/SDP4 propagation models for NORAD two-line element sets for added realism. Lloyd Wood