Developing new addon: asteroids larger than 250km

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bdm
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Developing new addon: asteroids larger than 250km

Post #1by bdm » 28.04.2006, 09:27

The standard asteroids list for Celestia only has the first four asteroids discovered (Ceres, Pallas, Juno, Vesta), plus an additional 12 of special interest.

The first four asteroids discovered are not the four largest asteroids. Ceres, Pallas and Vesta are three of the four largest asteroids, but Juno is a substantially smaller body that only ranks ninth in size (about seventh in mass) of the asteroids in the main asteroid belt.

The ten largest asteroids in size order are (source: Wikipedia):
1 Ceres
4 Vesta
2 Pallas
10 Hygiea
511 Davida
704 Interamnia
52 Europa
624 Hektor
3 Juno
87 Sylvia

Juno's ranking ninth in size would surprise many people. This is why I believe the creation of an addon that includes the other asteroids that are larger than Juno would be a valuable addon. It could even be incorporated into Celestia's main asteroid list.

I have tried creating orbits for a couple of the asteroids (I think I used the database at http://ssd.jpl.nasa.gov/sbdb.cgi) but I could not be sure I had the orbits right. When I created Ceres as a test, my version of Ceres was offset from the real Ceres by 30 degrees.
Last edited by bdm on 30.04.2006, 05:29, edited 1 time in total.

Topic author
bdm
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Post #2by bdm » 28.04.2006, 10:01

I found my error in the ssc file for Ceres. I used LongOfPericenter and it should have been ArgOfPericenter. When I made that correction the two copies of Ceres were much closer together.

I also used the database at http://www.alpheratz.net/murison/calcul ... ements.php

Here are two asteroids I have done so far. Are there any improvements I can make before including the orbital elements for the remaining bodies?

Code: Select all

#
# Asteroid list - asteroids with diameters larger than 250 km that are not in Celestia
# Compiled by bdm into celestia format
#
# Data sources
# ============
# List of largest asteroids: http://en.wikipedia.org/wiki/List_of_noteworthy_asteroids
# Orbital elements:          http://www.alpheratz.net/murison/calculators/OrbitalElements.php
# Rotation periods:          http://cfa-www.harvard.edu/iau/lists/LightcurveDat.html
# Albedoes:                  http://www.psi.edu/pds/archive/update05/albedo/data/albedos.tab
#
# There are 13 known asteroids larger than 250 km. Only 1 Ceres, 2 Pallas, 3 Juno and 4 Vesta are in Celestia
# The others are:
#
# 10 Hygiea
# 15 Eunomia
# 16 Psyche
# 31 Euphrosyne
# 52 Europa
# 87 Sylvia
# 511 Davida
# 624 Hektor
# 704 Interamnia
#

"Ceres_test" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.1132
    Radius               203.6
    EllipticalOrbit
    {
        Period           4.59870681
        SemiMajorAxis    2.76539484
        Eccentricity     0.08001022
        Inclination      10.586877
        AscendingNode    80.409695
        MeanAnomaly      129.983355
        ArgOfPericenter  73.231686
        Epoch            2453812
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       9.075
}



"Hygiea" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.0717
    Radius               203.6
    EllipticalOrbit
    {
        Period           5.55729311
        SemiMajorAxis    3.13744077
        Eccentricity     0.11823647
        Inclination      3.841847
        AscendingNode    283.458555
        MeanAnomaly      20.723915
        ArgOfPericenter 313.038262
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       27.623
}




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selden
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Post #3by selden » 28.04.2006, 10:49

bdm,

Rather than using "fan" sites, I'd suggest that you get current ephemeris data from the IAU's Minor Planet Center's database at the Harvard-Smithsonian Center for Astrophysics. That way you reduce the possibility of transcription errors or out of date information.

See http://cfa-www.harvard.edu/iau/mpc.html
and http://cfa-www.harvard.edu/iau/MPEph/MPEph.html
Selden

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bdm
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Post #4by bdm » 28.04.2006, 13:34

The original site I used did not give Julian dates for the epoch so I'm not using it any longer. I've just used this JPL site for orbital elements, with good results: http://ssd.jpl.nasa.gov/sbdb.cgi

With the orbital elements subject to change due to planetary perturbations, long-term accuracy is difficult to achieve.

To test the accuracy, I've included the JPL and IAU orbital elements for the first four asteroids in one file. The JPL and IAU elements give orbits that are fairly close together, and the Celestia asteroids are relatively far away. Perhaps Chris needs to update the orbital elements for the main asteroids?

The orbital elements for the first four asteroids are given here. The IAU elements are given as-is, whereas the JPL elements were rounded to 8 decimal places.

Code: Select all

# 1 Ceres
"Ceres_jpl" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.1132
    Radius               424.20
    EllipticalOrbit
    {
        Period             4.59879365
        SemiMajorAxis      2.76539484
        Eccentricity       0.08001016
        Inclination       10.58687960
        AscendingNode     80.40969394
        MeanAnomaly      129.98335927
        ArgOfPericenter   73.23169434
        Epoch            2453800.5  # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       9.075
}
"Ceres_iau" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.1132
    Radius               424.20
    EllipticalOrbit
    {
        Period             4.60
        SemiMajorAxis      2.7653949
        Eccentricity       0.0800102
        Inclination       10.58687
        AscendingNode     80.40970
        MeanAnomaly      129.98342
        ArgOfPericenter   73.23162
        Epoch            2453800.5  # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       9.075
}


# 2 Pallas
"Pallas_jpl" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.1587
    Radius               249.03
    EllipticalOrbit
    {
        Period             4.61591668
        SemiMajorAxis      2.77225498
        Eccentricity       0.23064442
        Inclination       34.84025148
        AscendingNode    173.14463064
        MeanAnomaly      114.18321229
        ArgOfPericenter  310.41822729
        Epoch            2453800.5 # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       7.8132
}
"Pallas_iau" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.1587
    Radius               249.03
    EllipticalOrbit
    {
        Period             4.62
        SemiMajorAxis      2.7722550
        Eccentricity       0.2306445
        Inclination       34.84024
        AscendingNode    173.14461
        MeanAnomaly      114.18325   
        ArgOfPericenter  310.41822
        Epoch            2453800.5 # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       7.8132
}

# 3 Juno
"Juno_jpl" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.1587
    Radius               249.03
    EllipticalOrbit
    {
        Period             4.35778813
        SemiMajorAxis      2.66791470
        Eccentricity       0.25827561
        Inclination       12.97125069
        AscendingNode    170.12397558
        MeanAnomaly       30.72778180
        ArgOfPericenter  247.83526289
        Epoch            2453800.5 # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       7.210
}
"Juno_iau" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.1587
    Radius               249.03
    EllipticalOrbit
    {
        Period             4.36
        SemiMajorAxis      2.6679148
        Eccentricity       0.2582755
        Inclination       12.97124
        AscendingNode    170.12404
        MeanAnomaly       30.72777   
        ArgOfPericenter  247.83519 
        Epoch            2453800.5 # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       7.210
}


# 4 Vesta
"Vesta_jpl" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.4228
    Radius               234.15
    EllipticalOrbit
    {
        Period             3.62857694
        SemiMajorAxis      2.36130502
        Eccentricity       0.08908830
        Inclination        7.13351097
        AscendingNode    103.92603212
        MeanAnomaly      232.80482680
        ArgOfPericenter  150.30944698
        Epoch            2453800.5 # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       5.342
}
"Vesta_iau" "Sun"
{
    Class                "asteroid"
    # Texture - goes here
    Color [0.5 0.5 0.5 ]            # Color is likely incorrect, assuming flat grey here
    # Mesh - goes here

    Albedo               0.4228
    Radius               234.15
    EllipticalOrbit
    {
        Period             3.63
        SemiMajorAxis      2.3613051 
        Eccentricity       0.0890882
        Inclination        7.13351
        AscendingNode    103.92607
        MeanAnomaly      232.80490
        ArgOfPericenter  150.30933
        Epoch            2453800.5 # 2006-Mar-06.0
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       5.342
}

Dollan
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Post #5by Dollan » 28.04.2006, 13:59

This sounds like an exciting project! I've always thought that the asteroids received something of a less-than-fair shake, and will be glad to see some accurate orbital representations of these subjects!

...John...
"To make an apple pie from scratch, you must first create the universe..."
--Carl Sagan

Topic author
bdm
Posts: 461
Joined: 22.07.2005
With us: 14 years 1 month
Location: Australia

Post #6by bdm » 28.04.2006, 23:48

I've got orbital elements for the 13 asteroids that have a radius larger than 125 km. A few notes:
  • This list has nine asteroids, not six.
  • I have not yet verified these for correctness. My method involved manual cut and paste, and it's possible I've made one or two errors.
  • All asteroids in this list are given with their name only, except for Europa, which is given as "52 Europa". This is necessary because this asteroid shares a name with a well-known moon of Jupiter.
  • I don't know how to assign colours to the asteroids. This is why all of them are grey. The source I have has U-B and B-V color indices but I don't know how to convert these to RGB, nor whether such conversion is possible with any degree of accuracy.
  • The source for the orbital data was the "JPL Small-Body Database Browser", http://ssd.jpl.nasa.gov/sbdb.cgi
  • Asteroids are given with radii, but most of the asteroids are not spherical. The actual shapes of the asteroids vary, but I lack the expertise to create suitable models.
  • All orbital elements are subject to significant change over time. This will be most noticeable with 624 Hektor, which is a Trojan asteroid.


Code: Select all

#
# Asteroid list - asteroids with diameters larger than 250 km that are not in Celestia
# Compiled by bdm into celestia format
#
# Data sources
# ============
# List of largest asteroids: http://en.wikipedia.org/wiki/List_of_noteworthy_asteroids
# Orbital elements:          http://ssd.jpl.nasa.gov/sbdb.cgi
# Rotation periods:          http://ssd.jpl.nasa.gov/sbdb.cgi
# Albedoes:                  http://ssd.jpl.nasa.gov/sbdb.cgi
#
# There are 13 known asteroids larger than 250 km. Only 1 Ceres, 2 Pallas, 3 Juno and 4 Vesta are in Celestia
# The others are:
#
# 10 Hygiea
# 15 Eunomia
# 16 Psyche
# 31 Euphrosyne
# 52 Europa
# 87 Sylvia
# 511 Davida
# 624 Hektor
# 704 Interamnia



# 10 Hygiea
"Hygiea" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.0717
    Radius               203.6
    EllipticalOrbit
    {
        Period             5.55739809
        SemiMajorAxis      3.13744078
        Eccentricity       0.11823654
        Inclination        3.84184137
        AscendingNode    283.45855625
        MeanAnomaly       20.72388364
        ArgOfPericenter  313.03828971
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       27.623
}


# 15 Eunomia
"Eunomia" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.2094
    Radius               127.67
    EllipticalOrbit
    {
        Period             4.29775312
        SemiMajorAxis      2.64335509
        Eccentricity       0.18707559
        Inclination       11.73780835
        AscendingNode    293.27363054
        MeanAnomaly      263.17170406
        ArgOfPericenter   97.89824531
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       6.083
}


# 16 Psyche
"Psyche" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.1203
    Radius               126.58
    EllipticalOrbit
    {
        Period             4.99046084
        SemiMajorAxis      2.92026076
        Eccentricity       0.13946251
        Inclination        3.09537975
        AscendingNode    150.34748320
        MeanAnomaly       62.21109199
        ArgOfPericenter  227.93351284
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       4.196
}


# 31 Euphrosyne
"Euphrosyne" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.0543
    Radius               127.95
    EllipticalOrbit
    {
        Period             5.59102942
        SemiMajorAxis      3.15008581
        Eccentricity       0.22600684
        Inclination       26.31714294
        AscendingNode     31.24084936
        MeanAnomaly      321.59775936
        ArgOfPericenter   62.01617773
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       5.531
}


# 52 Europa
"52 Europa" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.0578
    Radius               151.25
    EllipticalOrbit
    {
        Period             5.46453419
        SemiMajorAxis      3.10239170
        Eccentricity       0.10223880
        Inclination        7.46441555
        AscendingNode    128.95110760
        MeanAnomaly       88.52907454
        ArgOfPericenter  343.80533806
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       5.633
}


# 87 Sylvia
"Sylvia" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.0435
    Radius               130.47
    EllipticalOrbit
    {
        Period             6.51965067
        SemiMajorAxis      3.48988205
        Eccentricity       0.07971455
        Inclination       10.85685528
        AscendingNode     73.32899323
        MeanAnomaly       83.67460324
        ArgOfPericenter  265.95387233
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       5.184
}


# 511 Davida
"Davida" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.0540     
    Radius               163.03
    EllipticalOrbit
    {
        Period             5.63252329
        SemiMajorAxis      3.16565218
        Eccentricity       0.18561868
        Inclination       15.93890365
        AscendingNode    107.67208427
        MeanAnomaly      212.66376281
        ArgOfPericenter  338.56251275
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       5.1294
}


# 624 Hektor
"Hektor" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.025
    Radius               112.5
    EllipticalOrbit
    {
        Period            11.94604323
        SemiMajorAxis      5.22569333
        Eccentricity       0.02383973
        Inclination       18.19597287
        AscendingNode    342.80080721
        MeanAnomaly      134.73336010
        ArgOfPericenter  184.89172567
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       6.921
}


# 704 Interamnia
"Interamnia" "Sun"
{
    Class                "asteroid"
    Texture              "asteroid.*"
    Color [0.5 0.5 0.5 ] # Color is incorrect, assuming flat grey here
    # Mesh - goes here when created

    Albedo               0.0742
    Radius               158.31
    EllipticalOrbit
    {
        Period             5.35573480
        SemiMajorAxis      3.06107456
        Eccentricity       0.14965904
        Inclination       17.29208993
        AscendingNode    280.39627099
        MeanAnomaly      295.98816393
        ArgOfPericenter   95.80656116
    }
    Obliquity            0          # True value not known
    EquatorAscendingNode 0          # True value not known
    RotationPeriod       8.727
}
Last edited by bdm on 08.05.2006, 08:46, edited 2 times in total.

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Post #7by bdm » 29.04.2006, 02:22

If anyone is up to the challenge of preparing asteroid models, here is a scientific paper that models the shapes of some of these asteroids. This paper also provides axial tilts for some of these asteroids.

http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf

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Post #8by bdm » 30.04.2006, 08:38

UPDATE: I have checked the orbit figures given above. 511 Davida had the figure for the semimajor axis copied to the ascending node; the other figures were correct. I have corrected the figures.

All we need are textures and colours and it's good to go. Models would be good as well but they are not essential.

Can anyone offer suggestions on what would be suitable textures to use for these asteroids? I also don't know what colour they should be other than most of them being very dark.

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Post #9by bdm » 08.05.2006, 08:51

I have edited the list to include textures for the asteroids. Without knowing their true textures, I've chosen to give them the usual "asteroid.*" texture.

Most of these asteroids require models but I cannot make models for myself. So these will render as spheres, even though that is not really accurate. Juno is treated this way in the Celestia asteroids.ssc file so I think that should be OK.

I don't know what colour to set the asteroids, so I have left them with 50% grey. I notice that many of the asteroids in the Celestia asteroids file also skimps on colour information so I guess that's OK.

Would this be good enough for release?

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Post #10by ElChristou » 08.05.2006, 12:43

Bdm, for your asteroids model you can always use the default asteroid.cms; open it with a text editor and play with the values. You can do irregular spheres or whatever shape.

Concerning the whole addon, you should ask someone well skilled on those topics for a revision of your work before releasing (Grant Hutchinson?); this just to be sure all is 100% ok...

Anyway, Tx for the effort.
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Post #11by t00fri » 08.05.2006, 13:08

In early 2002 I have extracted already 7309 asteroids from the
official published scientific resources and produced a corresponding .ssc
file.

Here is a funny image from the time, where I artificially enhanced the
albedo of all these asteroids such that all of them could be seen at the
same time!

Image

Bye Fridger
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Post #12by ElChristou » 08.05.2006, 19:41

t00fri wrote:In early 2002 I have extracted already 7309 asteroids from the
official published scientific resources and produced a corresponding .ssc
file...


I suppose this mean the asteroids Bdm has extracted are already part of those 7309 bodies?
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Post #13by t00fri » 08.05.2006, 20:23

ElChristou wrote:
t00fri wrote:In early 2002 I have extracted already 7309 asteroids from the
official published scientific resources and produced a corresponding .ssc
file...

I suppose this mean the asteroids Bdm has extracted are already part of those 7309 bodies?


Certainly. The Universe is full of Asteroids. 13 are a rather small fraction...

Seriously: mass rendering of asteroids, say 250000 (!), are high on my todo list. But this is among the hardest mass-rendering tasks. The reason is that a proper octree structure (required for superfast rendering) is difficult to realize, since the asteroids are moving (unlike galaxies, for example!) . Yet I have some ideas to explore. We had that topic before, so I'll shut up now...

http://www.celestiaproject.net/forum/viewtopic ... sc&start=0

Bye Fridger
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Post #14by bdm » 09.05.2006, 03:22

ElChristou wrote:Bdm, for your asteroids model you can always use the default asteroid.cms; open it with a text editor and play with the values. You can do irregular spheres or whatever shape.

Concerning the whole addon, you should ask someone well skilled on those topics for a revision of your work before releasing (Grant Hutchinson?); this just to be sure all is 100% ok...

Anyway, Tx for the effort.

I didn't know that cms files were text files, thanks for the tip. Now all I need is to figure out how they work.

I have bookmarked on my other computer a scientific paper that gives approximate shapes for the majority of these asteroids based on light curve studies. Who knows, I may yet have reasonably accurate shapes for these asteroids.

Toofri's big list of asteroids would be useful for people who require many asteroids, but that's not what I need. My needs are a complete list of the largest asteroids which Celestia currently doesn't provide. In particular, I needed 10 Hygiea to be included because it's the largest asteroid that's not included in Celestia's standard list of asteroids. I chose to include other asteroids as well to show 3 Juno in its proper place as the ninth largest asteroid.

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Post #15by bdm » 14.05.2006, 06:35

I have a preliminary version of the addon available for download and evaluation at the following location: http://www.bdm.id.au/download/large%20asteroids%201-0.zip

Size of addon: 5 kb
Includes CMS models for 10 Hygiea, 15 Eunomia, 16 Psyche, 52 Europa, 87 Sylvia. (being CMS models, these models are very approximate)

I have checked the positions of 10 Hygiea and 15 Eunomia against asteroid ephemerides at http://cfa-www.harvard.edu/iau/MPEph/MPEph.html#summary

The SSC descriptions include rotation periods but not axial tilts and nodes.

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Post #16by t00fri » 14.05.2006, 09:35

bdm wrote:Toofri's big list of asteroids would be useful for people who require many asteroids, but that's not what I need. My needs are a complete list of the largest asteroids which Celestia currently doesn't provide.


My big list of course included also ALL the largest asteroids and the PERL script can easily sort and cut that list in size or magnitude according to individual needs! The list represented a complete, official asteroid catalogue. In addition an upgrade of respective ephemerides is only a CLICK in my case! Finally, no numbers were touched manually which greatly helps to avoid typos...

In general it is always a good idea to start Celestia projects from the /general/ side and specialize later. More people can profit this way and the solution is usually more versatile & "elegant" ;-)

If I'll find some spare time, I'll get back on this interesting culling task with /many/ moving asteroids. An appropriate octree structure in this case is kind of a math & coding challenge.

Bye Fridger
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Post #17by bdm » 14.05.2006, 11:10

Toofri, how detailed is your large asteroid addon? My addon includes rotation periods for all nine asteroids, and rough CMS models for five of them. At present I don't have Color, EquatorAscendingNode or Obliquity, nor do I have different textures.

The approach I have taken for my addon was to provide a complete inventory of the large asteroids, and provide some detail where I could find it. I wanted to have a small addon that could provide some extra asteroids that I believe should be in Celestia by default. I'm hoping that the addon could be developed to the point where it could be incorporated into the default installation of Celestia. If not, it will provide a choice of addons for those that may need it.

Oh, and Toofri, could you kindly post a download link for your addon if you haven't already?

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Post #18by t00fri » 14.05.2006, 12:17

bdm wrote:Toofri, how detailed is your large asteroid addon? My addon includes rotation periods for all nine asteroids, and rough CMS models for five of them. At present I don't have Color, EquatorAscendingNode or Obliquity, nor do I have different textures.

But why did you leave out EquatorAscendingNode and Obliquity? To reconstruct the complete orbits /precisely/ you need ALL orbital parameters and MUST transform them from the skyplane frame to the Celestia frame as usual, using quaternions. I suppose you did not ignore these required transformations?

The orbital parameters in the *.ssc files refer to the Celestia frame, while the ephemerides in the catalogs refer to the skyplane frame!

The approach I have taken for my addon was to provide a complete inventory of the large asteroids, and provide some detail where I could find it. I wanted to have a small addon that could provide some extra asteroids that I believe should be in Celestia by default. I'm hoping that the addon could be developed to the point where it could be incorporated into the default installation of Celestia. If not, it will provide a choice of addons for those that may need it.
The lack of asteroidal data in the Celestia distribution is just due to lack of (qualified) developer time. Like we have recently incorporated the /complete/ revised NGC/IC catalog of galaxies, Celestia's data base will certainly be expanded to also include entire published catalogs with planetary nebulae, galactic clusters...and asteroids.

We certainly would not deal with just a few at this advanced point of code development. As I said, if you have any clever ideas about how an octree might be constructed for asteroids that would be extremely helpful!

Oh, and Toofri, could you kindly post a download link for your addon if you haven't already?


[ note my username is t00fri NOT Toofri ;-) , but never mind]

I did that work on asteroids ~4 years ago and the actual .ssc file + PERL script must be dumped somewhere on some media. All I can readily find now was my asteroid image from that time.

Meanwhile we have changed the respective code structure completely (octree culling!) such that these lists have to be regenerated anyhow (which is very easy with PERL).

Also I am usually not involved with making add-ons. As a Celestia developer, my work will be rather integrated into the official distribution when everyone is content with the state of the art.

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Post #19by bdm » 15.05.2006, 00:42

t00fri wrote:But why did you leave out EquatorAscendingNode and Obliquity?
I think you have confused EquatorAscendingNode and Obliquity with Ascending Node and Inclination here. EAN and Obliquity defined the rotation axis of the body, and Ascending Node and Inclination are orbital parameters.

I don't ever intend to release any addon, no matter how incomplete, without a full set of orbital parameters.

On the other hand, I have omitted the rotation parameters because I have not yet found good data for these.

t00fri wrote:[ note my username is t00fri NOT Toofri Wink , but never mind]

Noted ... if you're particular about using zeroes instead of oes then I will take care to include them.

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Post #20by bdm » 15.05.2006, 00:55

t00fri wrote:To reconstruct the complete orbits /precisely/ you need ALL orbital parameters and MUST transform them from the skyplane frame to the Celestia frame as usual, using quaternions. I suppose you did not ignore these required transformations?

The orbital parameters in the *.ssc files refer to the Celestia frame, while the ephemerides in the catalogs refer to the skyplane frame!

What is the difference between the skyplane frame and the Celestia frame? I thought Celestia used orbital parameters in relation to the ecliptic.

I have checked the methodology by rendering Ceres, Pallas, Juno and Vesta in the same way and comparing the positions of these asteroids. The test asteroids were very close to the Celestia versions of the asteroids. I also checked two asteroids by using online ephemerides to compute the positions, and then comparing the positions in Celestia with the ephemerides. These also checked out to good accuracy. I intend to check the other seven in the next few days.


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