Technical progress -on Mars, where else

[Mahnmut]

Hello together,
I recently reread the magnificient Mars Trilogy by Robinson -again.
Motivated me to get my teeth into that unbelievably detailed Mars map again
https://planetside.co.uk/forums/index.php/topic,30470.0.html

Some of the problems I have solved, I can now use a downscaled version (about 20% resolution, 8 bit instead of 16) planetwide, which is still way better than what I had before.
And I can use a slightly downscaled version (ca 85% resolution, 8 bit instead of 16, so 50%vertical resolution?) for a quarter of the planetary surface.
I just set the spherically projected map to size 0.5x0.5 to use that quarter. Maybe someone can tell me how to do that with other quadrants than the southwestern one?
Anyway, I think there is some visible improvement:



First is my old 16k map, second the global downsized version, last the slightly downsized quadrant. The spheres diameter is 10 km.

[Mahnmut]

Before: 

Now :

[Hannes]

Indeed a significant progress! Well done.

[Dune]

Great! The only problem arising with 16 to 8 bit is that you easily get steps when heights differ much.

[Mahnmut]

Great! The only problem arising with 16 to 8 bit is that you easily get steps when heights differ much.

Yes, the steps are visible in the third greyscale pic above. But I am trying to optimize what I can get out of the limited filesizes I can use.
Do you have an idea how to position quarters or eights of an equirecatangular map on the sphere? That would solve the problem. Until now I can only use the lower left quadrant, which luckily includes the valles marineris. (I could of course use the other quadrants, but not together with a whole map.)

[Dune]

I don't know that, as I've never done it. But thinking about it, if it's one huge map, you could consider masking 3/4 off in Photoshop (4 times a different section), make it pure black, so together these 4 maps constitute the whole map. The maps may be a lot smaller to import (because of the 3/4 black), and you can overlap them in TG (add color) without changing positions. I don't know if that would work, just a thought.

Just a quarter of a spherical map would spread itself across the whole sphere. You could try and reduce the default 1-1 size to 0.5-0.5 and maybe flip a few quarters by X or Y (you would probably need to pre-flip them in Photoshop to get them right again in TG). But it might take translation too....
Just my 2 cents.

[Hannes]

That's what came into my mind as well. Ulco was faster!
Might be the easiest solution.

[Mahnmut]

Hi and thanks!
thats pretty much what I tried, with partial success.
Pure black does decrease filesize only in compressed files (that save 01111110 as 0(6x1)0. In uncompressed files a pixel is a pixel. On the other hand, I could try how the results look when using compressed tiffs.
A quarter map at 0.5x0.5 is what you see in the last pic works fine for the southwest quadrant (or any other of course) but not for a whole sphere, flipping only changes the orientation of the map, not where it is placed on the globe. translating it via input transform does nothing until at some value the map spreads over the globe, i do not understand that.
Thinking about Geog image map, but no success so far.
But getting closer.

[Hannes]

Is there a noticeable visual difference between a compressed and a non compressed tiff? I always used compressed tiffs and didn't notice any flaws.

[Stormlord]

@ Mahnmut
Very impressive details !

______________________________________________


-> Here are some good links regarding Mars

Best available Hi-Res true color photos of Mars
https://www.flickr.com/photos/132160802@N06/with/49411049033/

Best available Hi-Res Mercator maps of Mars
https://planetarymaps.usgs.gov/mosaic/
http://www.mars.asu.edu/data/
http://astrogeology.usgs.gov/search/details/Mars/Viking/MDIM21/Mars_Viking_MDIM21_ClrMosaic_global_232m/cub
https://astrogeology.usgs.gov/search/results?k1=map_projection_name&v1=Simple+Cylindrical



STORMLORD

[schmeerlap]

Nice red planet surface renders. The technical stuff kinda whooshed over my head 
ps. I cried out "FOUR" and everyone ducked, but we never did find that ball 

[Mahnmut]

Thanks!
At the moment I am just gnawing at this ginormous file that NASA generously provided, in order to cut it into parts I can use. If I succeed, i will hopefully use it in more creative images again.
I think the hint about lossless compressed files may be what I needed!
A 3/4 black map is smaller than 2 gb when compressed and so starts loading without error prompt. some seconds later though, I think when decompression reaches some treshold, TG crashes without further ado.
But one compressed half of the full map loads successfully. Now to see how many of these my PC can handle. 4 would be enough, west low, west hi, east lo, east hi.(high and low are distinct in the orignal map anyway)
So hold your thumbs if you like your red planet crisp!
Cheers,
J

[Dune]

That is the problem; compression saves disk space, but as soon as it's 'opened' it will be full size, same in jpg I guess. Maybe replace black for empty and one black dot in the other corner to keep the size, and save as png? I don't know what would be smallest once opened in TG.

[Mahnmut]

It works!
using two compressed halves each for low and high altitudes brings filesizes down enough, resolution should be 232 of the 200 m/pixel. Placing the halves works with a transform input shader. Glorious  global detail!


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[Hannes]

Wow, cool! Congrats! Looks gorgeous!