improvements for the forthcoming Celestia release
from the "galaxy front".
There are two aspects to the present galaxy project:
I) Code
--------
Since several months, I have implemented the
support of standard, (binary) PNG format for our
galaxy templates. As compared to the previous,
/non-standard/ pts format of Celestia 1.4.1, there are
many advantages, as I described in various previous
posts. Here is a brief summary:
-- storage requirements are only << 1/10 of the .pts
format! Hence many more templates beyond the
standard Hubble classes may be designed easily.
-- since PNG is a standard format (unlike .pts)
everyone may use his favored image manipulation
program and play with or design new templates. All the
fancy options like layers etc may be applied and are of
paramount importance, in fact, for good
brightness-normalized designs.
--I have recently added the often requested option of
custom templates for any of the 10000+ galaxies of
my deepsky.dsc catalog. Notably, this is crucial for the
MilkyWay (see below)!
--PNG's can carry color and alpha, i.e. useful additional
degrees of freedom for future improvements/
enhancements of our templates!
II) Template design
--------------------
Well this is a most enjoyable scrupoulos joint project
with ElChristou (aka Christophe) since quite a while.
Christophe has invented a systematic layer design
algorithm for PNG galaxy templates that is really great.
He (and I?) will soon write a tutorial in CelestialMatters
as soon as some spare time pops up!
As soon as possible, Christophe and/or I will present
here a more systematic status report about our new
PNG templates.
Obviously, I can only commit the new galaxy code once
our joint template design effort is completed as well
We are working hard to finish it ASAP!
++++++++++++++++++++++++++++++++++++++
Today, I want to focus on some exciting new display
improvement for our galaxies that I discovered only a
few days ago.
++++++++++++++++++++++++++++++++++++++
What does it amount to??
It concerns making our galaxy templates "voluminous" in just the right way:
Remember our galaxy templates are only 2-dimensional
to start!
The idea is absolutely simple. In galaxy.cpp, I calculate
the 3rd coordinate (i.e. the "thickness" of the spirals)
proportional to the read-in template brightness value at
the point (x,y)! Unlike previously, where the spiral
"thickness" was generated randomly as a (thin)
uniform Gaussian shape in an initialization method, it's
now mainly the /bright center and the bright arms/
that become "non flat".
So let me list the recent progress as emerging from my
new code in turn:
A) First, here you see the present status of ElChristou's
actual custom template design of our new MilkyWay,
that contains ALL scientifically established arms, the
correct size and inclination of the central bar and, of
course, the Sun in proper location. Lots of joint tuning
and discussions went into that! I now display our latest
MilkyWay with annotations of arms etc, according to
my new 3d code. Note the enhanced 3d impression in
the central region:
B) The next striking benefit of my new code is this:
If spirals are now viewed /sideways/, one notices these
typical thin dark regions that were badly missing so
far. This is illustrated in the next composite image. The
top galaxy is the custom MilkyWay from A) viewed
sideways! Note the dark central lane! The next one is a
different Hubble class and compares well to an actual
photo in the lowest image!
C) It turns out that my new code gives not only a great
3d impression, but also precisely the right /transverse
widening/ of the MilkyWay arms as is observed from
Earth! The latter constraint gave us quite some
headache, as you may see first from ElChristou's nice
comparison with a photo mosaic (exaggerated colors!)
of the center of the MilkyWay as seen from Earth
With my new code the central part of the Milky way is
almost spot on, shows the striking dark lane and even
about the right colors!
So I am busy to try some further explorations of this
idea and to implement some fine tuning.
To end, here are just two "appetizers" in form of two of
our new PNG templates: Hubble class Sc (M74) on top
and SBc, with a conspicuous bar.
Cheers,
Fridger
!, no ?
