New spiral galaxy types rendering

[Cham]

And what if I compile you a Windows version close to the weekend? It's your fault to run OS X though .

Bye Fridger

AAARRrrghh! Teaser ! You deamon !

Dirkpitt ? h-e-l-p !

[selden]

Fridger,

I'm not sure which Messier catalog you used. I created several.

The earliest (v1) catalog should have reasonably accurate positions, I think. It only marked the locations of the Messier objects in Celeatia. I extracted those locations from the original "galaxies.dat" which was created by "Paul" in Australia. I'll admit that I didn't take the time to verify them.

The later catalogs (v2 and later), which included pictures, had the positions adjusted so that the pictures were properly positioned in Celestia. The centers of the pictures usually were not near the cataloged positions of the objects.

Is this consistant with what you see?

[julesstoop]

I have one huge gripe/criticism (though the improvement is huge, don't get me wrong)
The nuclei of the galaxies in the new celestia code from all the comparisons posted by Fridger are by no means dense/strong enough compared to the real thing.

[Cham]

I have one huge gripe/criticism (though the improvement is huge, don't get me wrong)
The nuclei of the galaxies in the new celestia code from all the comparisons posted by Fridger are by no means dense/strong enough compared to the real thing.

Yes, that's what I've said earlier. The galactic center (nucleus) isn't strong enough.

[t00fri]

Fridger,

I'm not sure which Messier catalog you used. I created
several.

The earliest (v1) catalog should have reasonably accurate
positions, I think. It only marked the locations of the Messier
objects in Celeatia. I extracted those locations from the
original "galaxies.dat" which was created by "Paul" in
Australia. I'll admit that I didn't take the time to verify them.


The later catalogs (v2 and later), which included pictures, had
the positions adjusted so that the pictures were properly
positioned in Celestia. The centers of the pictures usually
were not near the cataloged positions of the objects.

Is this consistant with what you see?

Selden,

of course, I used your latest (v3) from the Motherlode and
threw away the pictures (sorry), but we want to make them
here ourselves in thousands

The galaxy input lacks the min/max extension parameters,
hence a proper size and inclination can hardly be computed.
Also the position angle of the major galaxy axis is lacking. So
the resulting orientation is random as far as the info from
your 'messier_galaxies.dsc' file. I am not using anything else
that that for the tests.

Towards the weekend, I shall certainly Perl-extract all
required numbers from Steinicke's catalog, such that we have
a state of the art basis for comparisons available in form of
thousands of galaxies.

Bye Fridger

[t00fri]

I have one huge gripe/criticism (though the improvement is huge, don't get me wrong)
The nuclei of the galaxies in the new celestia code from all the comparisons posted by Fridger are by no means dense/strong enough compared to the real thing.

That's peanuts. Don't worry. Work ahead for the weekend. I described further above what I have in mind concerning colors and luminosity distributions.

Bye Fridger

[julesstoop]

:D

That would be great. I really feel galaxies as they are: mostly with a very dense centre.

[dirkpitt]

And what if I compile you a Windows version close to the weekend? It's your fault to run OS X though .

Bye Fridger

AAARRrrghh! Teaser ! You deamon !

Dirkpitt ? h-e-l-p !

Too bad, like t00fri you'll have to wait until the weekend for an OS X test version. Got an exam tomorrow that is sucking up my time like a supermassive black hole.

[Toti]

Paulo & Toti,

you seem to find the above image a big improvement. Unfortunately, I don't. It doesn't really look much like a galaxy anymore. The boundaries are way to sharp and the "fluffyness" is entirely gone. I agree that one might use /elements/ of this for inside areas of galaxies.

The image was rendered using the same 3d model and color table that I already published. The only change is that I switched back to the old blending mode (used in the standard Celestia code) The new algorithm also sorts the particles in order to achieve certain effects.

It was meant as a quick demonstration of "opaque" blobs blocking light coming from the bulge (ie. it's a rotation/scaling sequence from the bottom-right to the upper-left corner). Unfortunately these days I don't have enough spare time to tweak the color table to enable real dark clouds and make the boundaries more transparent.

Bye

[t00fri]

Hi all,

since the weekend has arrived, I want to let interested people know what I have decided to work on first and what the inherent challenges are:

In order that we shall be able to judge our progress in galaxy rendering/coding continuously and realistically, I decided to start off with the PERL extraction of 10000+ galaxies from Steinicke's latest catalog (April 2005) with 14000+ deepsky objects.

That is a straightforward task and should be completed within an hour of work. Another straightforward but somewhat more tedious task is the conversion of catalog parameters (RA, DEC, minor major sizes and position angles) referring to the Sky-plane into Celestia's DSC input scheme, based on the ecliptic plane with orientations and sizes given as AXIS [a,b,c] and ANGLE= d [degrees] and RADIUS . Although one may easily get some signs wrong here the manipulations just amount to multiplying a few quaternions together (in the right way ) . That will all be implemented in my PERL code, such that the output will be directly a galaxy.dsc file, readable by Celestia.

The big point is of course what catalog information we want to make use of in addition? Certainly we want besides magnitudes also some color and surface brightness ( Bmag & SB). I shall already extract these quantities now but ask PERL to comment those entries out that Celestia does not know already. Then we may easily experiment with this additional info later.

You see, since PERL is very good at doing also calculations, the idea would be to calculate color profiles (and possibly other features) with PERL for each of the 10000+ galaxies /outside/ of Celestia! This saves CPU time and provides a /human-readable/ documentation of what was actually done.

In general terms (applying e.g. also for binary orbits), the idea would be to eventually include the PERL scripts into the distribution. This is a perfect way of documenting in human-readable form what modifications relative to the published catalog data where applied in Celestia's data displays!

Also I will get hold of alternative names besides NGC and IC, notably the Messier numbers should be there. This might require cross-referencing ...

Earlier in this thread I displayed the available catalog entries so that people may check what might be useful quantities in addition:

http://www.shatters.net/forum/viewtopic.php?t=7012&postdays=0&postorder=asc&start=18


Clearly with very few modifications, I then may go on producing extensive catalog input about open/galactic clusters, (planetary) nebulae etc...

Bye Fridger

[selden]

I'd be quite willing to replace the catalogs that I have with the ones you generate, if you want. Or are you anticipating distributing them with Celestia?

One problem is that displaying a large number of galaxies can slow Celestia significantly. It seems to me that, as others have suggested previously, it'd be really nice if there were some way to select different catalogs to be displayed rather than just all galaxies or none.

[t00fri]

I'd be quite willing to replace the catalogs that I have with the ones you generate, if you want. Or are you anticipating distributing them with Celestia?

One problem is that displaying a large number of galaxies can slow Celestia significantly. It seems to me that, as others have suggested previously, it'd be really nice if there were some way to select different catalogs to be displayed rather than just all galaxies or none.

Selden,

I suppose that stuff should go to the official distribution. We may always discuss whether the number of galaxies (and other deep sky objects) should be cut down to some sensible subset. With Perl this is just one line of code...

I agree, the possibility to select among different catalog data sets should be incorporated via some GUI tool. For me this is the only kind of "justification" for incorporating a loose "relative" of a download manager

Bye Fridger

[t00fri]

Whoever has some interest in the power of PERL,

in PERL, there is a great module for about every sensible task....

I cannot resist showing you, how simple and elegant the task of rotating deep-sky objects from the sky-plane to the Celestia ecliptic coordinate system becomes with the appropriate PERL modules:

Here is the whole script that can do the job for thousands of galaxies, illustrated in case of the Andromeda galaxy (M31) with (RA=0.712h, dec=41.27 deg). The code is the equivalent of Grant's EXCEL worksheet code (dsc.xls), which due to EXEL grammar, looks rather unelegant...

----------------rot.pl------

Code: Select all

use Math::Trig;
use Math::Quaternion qw(slerp);

$decrot = Math::Quaternion::rotation(deg2rad(41.27-90),1,0,0);
$rarot  = Math::Quaternion::rotation(deg2rad(0.712*15-90),0,1,0);
$eclipticsrot = Math::Quaternion::rotation(deg2rad(-23.4392911),1,0,0);
$rot=Math::Quaternion::multiply(Math::Quaternion::multiply($eclipticsrot,$rarot),$decrot);
$angle=$rot->rotation_angle*180/pi;
@v=$rot->rotation_axis;
print "Axis = [@v],\nAngle = $angle\n";


-----------------
The output is the desired Angle-Axis quaternion:

Code: Select all

Axis = [-0.579159397502715 -0.795440302826062 -0.178463208881482],
Angle = 103.053563075768


This corresponds to an object pointing towards North and being "face-on" to the sun. With just another quaternion one now may implement the galaxy's position angle and inclination (computed from the major and minor extensions given in the catalog) ... it's as simple as that.

Bye Fridger

[maxim]

I agree, the possibility to select among different catalog data sets should be incorporated via some GUI tool. For me this is the only kind of "justification" for incorporating a loose "relative" of a download manager

Summarizing this comment and a discussion from another thread, I'd say this is the central point of creating an addon manager utility - it's purpose would be shurely not to ease the collecting of oh-so-many addons for noobs, but to deal with the 3245. version of a certain addon or addon catalog ('do I have the latest update, or do I not?'). For any reason you always neglected that point.

maxim

[danielj]

Very well,but I would like to see pictures of different galaxy types,side by side,showing the differences in rendering between a Sa,Sb,Sc,SBa and so on.Is it possible?

[t00fri]

Very well,but I would like to see pictures of different galaxy types,side by side,showing the differences in rendering between a Sa,Sb,Sc,SBa and so on.Is it possible?

Almost everything is possible it just takes time. Why should I do that? Just to please you?

Actually, further up in this thread I compared the rendering of a number of well-known galaxies to their DSS photographic images. Mostly they corresponded to different Hubble types.

That's almost what you asked for.

Bye Fridger

[danielj]

Sorry,I didn??t saw all the pages of this thread

Very well,but I would like to see pictures of different galaxy types,side by side,showing the differences in rendering between a Sa,Sb,Sc,SBa and so on.Is it possible?

Almost everything is possible it just takes time. Why should I do that? Just to please you?

Actually, further up in this thread I compared the rendering of a number of well-known galaxies to their DSS photographic images. Mostly they corresponded to different Hubble types.

That's almost what you asked for.

Bye Fridger

[ArneB]

I love the new looks of the galaxies! Better visuals make Celestia so much more fun. And the depth sorting will make sideviews truly stunning. One thing though, is it possible to replace the blobs with custom bitmaps? (of low quality) That could make the galaxies more whispy and less blobby. Anyhow, the new rendering is really great!

[dirkpitt]

I managed to eliminate color fringing and galaxy flickering. This patch file should be applied immediately after applying Toti's galaxy patch:

* galaxyPatchPatch.diff

The color fringing was caused by a buffer overrun when looking up the color table (index could be > 255).
The flickering was caused by a classic perspective projection imprecision problem. I modified render.cpp to
enable the existing fix that moves the near clip plane closer to the object. Previously it would only apply the
fix when the object radius was < 10, but now it also checks if the object's projected size is very small compared
to its actual size.

[Cham]

I managed to eliminate color fringing and galaxy flickering. This patch file should be applied immediately after applying Toti's galaxy patch:

* galaxyPatchPatch.diff

The color fringing was caused by a buffer overrun when looking up the color table (index could be > 255).
The flickering was caused by a classic perspective projection imprecision problem. I modified render.cpp to
enable the existing fix that moves the near clip plane closer to the object. Previously it would only apply the
fix when the object radius was < 10, but now it also checks if the object's projected size is very small compared
to its actual size.

Dirkpitt,

how do you apply this patch on the OS X version ? I guess it's only for the developpers ?