Corrected Eros model and rotational parameters

[granthutchison]

Celestia's Eros model is mirror-reversed, again, I think, because the original shape data are provided in east longitude rather than west longitude. I've generated a detailed replacement shape model (mapped at 2-degree resolution), and Selden has made it available on his site:
http://www.lns.cornell.edu/~seb/celestia/hutchison/#4.1
This one won't accept a texture in Celestia (I've been unable to export the big VRML file to 3ds), but it really doesn't need one - the crater detail on the model is quite impressive. The only textures for Eros I've seen so far are a shaded-relief map and very lo-res photomosaic prepared by Phil Stooke after the 1998 NEAR fly-by, and a rather horrible gridded and labelled photomosaic showing suggested feature names. I've tried all of these in VRML, and they just obscure the detail of the hi-res shape model. There are also noticeable errors in Stooke's old shaded-relief map when it's laid on to the current detailed shape model. However, I'm hoping to make a 5-degree shape model available soon, which will accept textures for those that want to use them.

I've generated correct rotation parameters for Eros, and I've also downloaded the correct orbital parameters for the date of the 1998 NEAR fly-by. The Eros definition for solarsys.ssc looks like this:

Code: Select all

"Eros" "Sol"
{
   Class "asteroid"
   Mesh   "eros2.3ds" #corrected mesh
   # Color sampled from true color photo taken by NEAR
   Color   [ 0.52 0.47 0.42 ]
   BlendTexture true
   Radius 16.5

   EllipticalOrbit
   {
   Epoch           2451171 #23 Dec 1998 12:00 
   Period            1.761
   SemiMajorAxis     1.458261
   Eccentricity      0.222885
   Inclination      10.830143
   AscendingNode   304.430882
   ArgOfPericenter 178.613184
   MeanAnomaly     208.403434
   }

   RotationPeriod         5.270
   Obliquity             78.70
   EquatorAscendingNode 107.23
   RotationOffset       158.16

   Albedo            0.16
}


This recreates the 1998 NEAR encounter quite nicely. (So you can check this out easily, I've included a sampled orbit for NEAR in the zip file along with the Eros model, covering the three days around the Eros fly-by.)
But I'd guess that to recreate the complexities of the 2000 orbits and "landing" we're going to need sampled orbits for both NEAR and Eros, and a bit of tweaking of the rotation parameters - I'm off to start playing around with that now.

Grant

[granthutchison]

As promised, a lower resolution shape model for Eros that does take a texture in Celestia:
http://www.lns.cornell.edu/~seb/celestia/hutchison/#4.2

In the absence of any good Eros textures I can find, I've made one myself -I've included it along with the above shape model. It's a 2k shaded-relief map, prepared from the one-eighth-degree NEAR altimetry data, and it makes the small shape model look rather nice.

Grant

[chris]

As promised, a lower resolution shape model for Eros that does take a texture in Celestia:
http://www.lns.cornell.edu/~seb/celestia/hutchison/#4.2

In the absence of any good Eros textures I can find, I've made one myself -I've included it along with the above shape model. It's a 2k shaded-relief map, prepared from the one-eighth-degree NEAR altimetry data, and it makes the small shape model look rather nice.

Grant

The texture map looks great . . . But what would be ideal is a 2k x 1k bump map generated from the one eighth degree altimetry data. The elevations in the bump map could be generated by computing the difference between 1/8 degree samples and linear interpolation of 2 degree samples. Or you could just compute the gradients directly for a normal map . . . that might be easiest. Where is the one eight degree data set?

--Chris

[granthutchison]

Where is the one eight degree data set?

http://pdssbn.astro.umd.edu/NEARdb/nlr/#shape
It's in a mildly user-belligerent file format, with a scale factor and an offset applied to the data.

Grant

[chris]

Well, I created a bump map from the one eighth degree altimeter data, and then realized that Celestia doesn't currently support bump mapping on non-spherical objects. So, that's something that I'll have to implement now :>

Using the pbm tools on Linux, I converted the .img file into a 16-bit TIFF and then generated a normal map with the NVIDIA tools. In case anyone's interested, the 2880x1440 16-bit TIFF is here:

http://www.celestiaproject.net/~claurel/pics/foo.tif

--Chris