FAQs
Sure! The installation is complex, and you'll need to have an already running copy of IDL, Apache,
SPICE, and subversion. But if you're interested, be in touch. Several users have installed their own.
I want your suggestions! Please let me know. If you want to add a new feature which you've written, by
all means be in touch.
Yes! All of GV's parameters for the current plot are passed on the URL. If you copy that URL, you can
e-mail to others, save it yourself, bookmark it, or anything else you'd like to do.
You're probably using GV's Rectangular display projection. Switch to Spherical mode and to reduce
apparent distortion. Rectangular mode is useful because lines of RA/Dec are straight when projected onto
the sky. Spherical mode preserves the shape of planetary bodies, but distortis lines of RA/Dec to be
curved. Calculations and positions are equally accurate in both modes.
The slowest portions of the code relate to rendering large wireframe images (e.g., ones that fill the
screen), and to searching a large portion of the sky with the HD or USNO-B1.0 star catalogs (e.g., >5
deg for HD, or >1 deg for USNO-B1.0). To speed things up, zoom out from planets, zoom in on stars, and
change the star catalog to Tycho-2. Turn off star plotting and/or planet plotting. Data tables of planet
positions are made regardless of whether the planets themselves are plotted.
There is a bug which occasionally causes GV to timeout, and reloading the page does not work. If this
fails, it can almost always be fixed by quitting your browser entirely (copy the URL first), and then
reloading the same URL.
Please report it! I get a lot of bug reports, and they all help to make GV better.
GV's bottleneck is surface rendering. Loading large HTML tables is a close second, along with star
catalog searching. To speed things up, turn off Draw Planets and Draw Satellites. Turn off all 'Show
data tables...' options. Then hit Plot. Tables of planetary positions take ~15 seconds to generate for
1000 timesteps. Once generated, the tables can be downloaded as CSV files, even when they're not
displayed to the screen by GV.
Nix & Hydra have non-keplerian orbits. GV computes the positions accurately (they're taken directly from
SPICE), but uses its own routines to plot the orbit ellipses. The ellipses drawn assume circular,
non-inclined orbits, and differ by a few pixels for some satellites, like Pluto's. For other satellites
(Moon, Himalia, Elara), the orbit ellipses would be far off, and are not drawn at all.