Posts by scalbers

by scalbers
24.04.2017, 17:15
Forum: Textures
Topic: Planetocentric vs Planetographic maps
Replies: 10
Views: 3260

Re: Planetocentric vs Planetographic maps

I think the link the show is the one by Paul Schenk on the planetographic projection. Indeed Hershel looks too elongated. We'll know if things are projected right in Celestia if the appearance is more round. I would also tone down the color on that map if visual realism is desired.
by scalbers
20.04.2017, 17:46
Forum: Textures
Topic: Planetocentric vs Planetographic maps
Replies: 10
Views: 3260

Re: Planetocentric vs Planetographic maps

Perhaps a dem wouldn't really be needed with 'gdal'. More a specification of map parameters. This would also help for converting and displaying my planetocentric map of Mimas. http://stevealbers.net/albers/sos/sos.html#MIMAS There is a planetographic version of Mimas from Paul Schenck, so this means...
by scalbers
17.04.2017, 23:00
Forum: Textures
Topic: Planetocentric vs Planetographic maps
Replies: 10
Views: 3260

Re: Planetocentric vs Planetographic maps

Possibly GDAL can be downloaded for Windows here:

http://trac.osgeo.org/gdal/wiki/DownloadingGdalBinaries
by scalbers
17.04.2017, 18:39
Forum: Textures
Topic: Planetocentric vs Planetographic maps
Replies: 10
Views: 3260

Re: Planetocentric vs Planetographic maps

Perhaps two sets of parameters would be useful. One could describe the projection of the texture, and another for the actual displayed shape of the object? I have coded (in IDL) some equations for (at least approximately) doing some of these conversions. 'gdal' sounds good as well as it could be eas...
by scalbers
13.04.2017, 23:05
Forum: Add-on development
Topic: Programs for UV mapping partial textures to an object
Replies: 6
Views: 1550

Re: Programs for UV mapping partial textures to an object

FYI, I notice this script to export a 'cmod' format file from Blender.

https://www.blender.org/forum/viewtopic.php?t=8352
by scalbers
07.04.2017, 21:38
Forum: Ideas & News
Topic: Virtual space telescope inside Celestia?
Replies: 14
Views: 3810

Re: Virtual space telescope inside Celestia?

It seems like a certain amount of zoom will produce an image of a planet that is say 10 pixels wide. This would indeed produce an "out of focus" appearance of the planet. Are you suggesting that if you even zoom in more than this to make it a bigger image it should only have the same amoun...
by scalbers
07.04.2017, 21:13
Forum: Ideas & News
Topic: Virtual space telescope inside Celestia?
Replies: 14
Views: 3810

Re: Virtual space telescope inside Celestia?

It looks like they are doing some interesting calculations of what the detailed spectrum looks like, and that is useful to help get more accurate color. This is along the lines of the DSCOVR comparisons and simulated imagery I've been referring to in some related threads.
by scalbers
07.04.2017, 18:26
Forum: Ideas & News
Topic: Virtual space telescope inside Celestia?
Replies: 14
Views: 3810

Re: Virtual space telescope inside Celestia?

Could one simply zoom in with a high magnification?
by scalbers
05.04.2017, 16:27
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Titan: Blue and Orange

If we assume most of the scattering effects are from aerosols, why does Titan look blue at the high levels and orange when looking lower down? An important factor could be that at high altitudes the aerosols are thin. Single scattering and the effects of the Angstrom exponent are dominant with more ...
by scalbers
03.04.2017, 17:41
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

Indeed quite the video and I think it does a good job with the details of seeing the sun from the surface and with the color of the light. Judging from the paper though the blue sky at high altitudes could (depending on phase angle perhaps) be just as much from fine aerosols as from Nitrogen. This r...
by scalbers
02.04.2017, 13:19
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Titan views

I'm still considering how to render Titan's sky from the surface. This University or Arizona animation shows a more uniform sky even near the sun without an aureole. This makes sense the more I think about it. The sun and sky color look pretty good. It's a quite well done rendering of the descent an...
by scalbers
31.03.2017, 19:03
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

Sounds good - the first link two posts up is from a reissue of a book from Carl Sagan. I think Venus' planetary albedo is around 75% so there would be three definitions. I'm unsure what the difference between planetary and Bond albedo is, they appear to be the same as per the values given in the lin...
by scalbers
28.03.2017, 16:45
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

CO2 is pretty dominant and has a large Rayleigh scattering cross-section (see below). The thing I'm wondering is with all that Rayleigh scattering, how any of the light makes it to the surface instead of being bounced. Here is a good summary. http://link.springer.com/referenceworkentry/10.1007%2F978...
by scalbers
27.03.2017, 17:28
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

I agree that land BRDFs (or phase functions) would be helpful with adding an opposition surge. A blue rim sounds reasonable. It turns out that the 27 magnitudes only applies to direct sunlight. Since much of the scattering is in the forward direction, about 30% of the sunlight will filter down to th...
by scalbers
24.03.2017, 17:49
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

Looks like Venus has a glory seen from above: https://arxiv.org/pdf/1406.0277.pdf Elsewhere I can note an optical thickness of around 25 for Venus clouds. Possibly the CO2 in the atmosphere add another 15 with Rayleigh scattering, coloring Venus more blue? Only 2.5% of solar radiation is absorbed in...
by scalbers
23.03.2017, 23:09
Forum: Textures
Topic: Whole Earth View
Replies: 61
Views: 13447

Re: Whole Earth View

I do have an automatic brightness scaling that depends on how far below the horizon/limb the sun is. Thus it would be the relative brightness in different portions of the sky that would be important. We could adjust the brightness of either of our images somehow to get a closer comparison. Interesti...
by scalbers
23.03.2017, 17:26
Forum: Textures
Topic: Whole Earth View
Replies: 61
Views: 13447

Re: Whole Earth View

For the fully lit Earth the hazy appearance is more from Rayleigh scattering and the crescent or high phase angle view is affected more by Mie (when forward scattering is properly introduced). The brownish appearance in the second image of post #52 tells me the Mie absorption may be overdone. The im...
by scalbers
23.03.2017, 17:19
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

Sounds good. There is a bit of a distinction I can suggest in that the color of the clouds (in the real Venus) is actually caused by differential absorption. Maybe there's a distinction between the absorption occurring during the scattering process and absorption as light transverses larger cloud dr...
by scalbers
22.03.2017, 18:58
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

Here are a couple of images for comparison, with some good explanations: http://mentallandscape.com/Venus_Visible.htm http://www.donaldedavis.com/2002_addons/SSYCOLRS.html (scroll to see Venus) Otherwise, the redundancy I was thinking of would be a white texture with the absorption turned on vs a hi...
by scalbers
22.03.2017, 17:24
Forum: Celestia Users
Topic: Planetary Atmospheres Light Scattering
Replies: 46
Views: 11005

Re: Planetary Atmospheres Light Scattering

Indeed Venus is a good object for reference and your views look fairly close. With thick clouds like Venus the "effective" asymmetry is smaller and one runs into questions about how asymmetry (that relates more to thin clouds) transitions into reflectance as thick clouds behave somewhat mo...

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