Celestia Forums

Hello t00fri,
Thank you for the work done on the Moon's textures. This thread has
a purpose. A calm, articulate discussion may occur here about logical
and scientific displays of the Moon in Celestia 1.4.1 and in general.

What does a bump jpeg texture do?

Does it interact with the rays from the Sun to cast shadows in variable
directions?

In a few months, a greatly improved "2006 topo" database will be
published by USGS., according to :


Dr. Randolph L. Kirk
Astrogeology Team
U.S. Geological Survey
2255 N. Gemini Dr.
Flagstaff, AZ 86001 USA

He will notify me when it is published. It is expected between
February and June 2006.
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2106.pdf

The Celestia 1.4.1 Moon uses a 2002 elevation model that is noted in the README file.
I looked at the gif and jpeg gray images and they are
appalling. Take a look :
ftp://ftpflag.wr.usgs.gov/dist/pigpen/m ... po/global/
The text file burys the sad news about the inaccuracy of this 2002 model:

"the Clementine laser altimeter collected an elevation value for
every 514 km2; and the photogrammetric data collected an
elevation value for every 1.3 km2"

This mismatch is easy to see in the jpeg pictures.

Also, get this :

"For the south pole region the stereo topographic data is an
average of 163 m lower than the Clementine laser altimeter points,
with a standard deviation of 1005 m. "

If I am interpretting this correctly, the topo model is severely flawed.
In the Users Forum, I asked some questions :

1
Is the Clementine data from the 1996 publication? No, 2002

2
Is there new topo data from Clementine from 2005-2006? No, but soon.

3
Where can I get any new 2005-2006 published topo data from Clementine? Dr. Randolph Kirk.

4
What should I see on the New Improved Moon that is better than the
old Moon? It looks smoother. It is less bumpy.

5
Is it the bump jpg that is improved? Yes.

But what does a bump map do, in detail? I assume that a jpeg bump
file does not make 3D shapes be displayed in Celestia on my 2D monitor.
Does Celestia use the jpeg bump info to draw shadows according to the Sun's rays?
I would appreciate an articulate description. Are shadows imposed on the
Moon image according to rays and tilt of the limb at each latitude and longitude?

GM,

since the concept of bump mapping is a most basic subject in any image manipulation tutorial, it would be a vaste of my time to repeat this once more, while it takes you a few clicks in the net to retrieve good respective explanations. I gave the first "lectures" about this stuff here almost 4 years ago...

GM wrote:n a few months, a greatly improved "2006 topo" database will be
published by USGS., according to :


Dr. Randolph L. Kirk
Astrogeology Team
U.S. Geological Survey
2255 N. Gemini Dr.
Flagstaff, AZ 86001 USA

That is indeed VERY good news. I can't wait to see these new data.

GM wrote:I looked at the gif and jpeg gray images and they are
appalling.

That is of course NOT what I committed to CVS. There was quite a lot of tuning, repairing and polishing work in between the original (raw) data referred to in the README and what I finally submitted to CVS. Yet I cannot make the content of these files "richer" than what it is...Nevertheless, the result based on my /2k/ bump-map is WAY better than what we had before. There is NO doubt about that. I repeat that with only /1k/ base textures the "3d" lever arm is kind of marginal...

A good way of visualizing the effects of the bump map is to switch from the OPENGL 2.0 render path to the Basic rendering by a single CTRL+V hit. The "Basic" render path cannot handle bump maps. So you can compare their effect well.

Bye Fridger

Hi t00fri,
Thank you for pointing out the render path's effect on the bumps on the Moon.
This is the first time the "control v" had any effect on something I
was looking at. Also I read up on what bump jpegs do : they make
the normals change directions.

Now for the bad news : the new bump jpeg file is worse than the old one.
It is true that the new one more accurately shows that state of the art
Clementine topo data, but that Clementine data is severely flawed. The
Celestia users can easily look at the Moon's limb under grazing sun ray
incidence and see the vertical stripes. These clear vertical stripes are not
realistic. They are the result of the defective Clementine data. Please
consider reverting to the old bump jpeg file. The old one does not show
the technical state of the art. It was art. It was good.

In case the users do not know what to look for, I am providing an exaggerated
Moon 3D model image for their 2D screens. The Clementine
elevations were exaggerated by 25x to make this .stl model :

The exaggeration is only useful here to let the users focus their attention
on the probelm. The Celestia Moon's problem is not so obvious as in the
exaggerated model.

Conclusion
Thank you t00fri for all the hard work you put into attempting to improve
the Moon's bump texturing normals. It is sad that the Clementine data
has degraded the resulting visual display. It's not your fault. Please
don't take it too hard. I will let you know when the improved Clementine
data is published this Spring.

Alan Folmsbee, Globe Maker