Science Project Lunoid

T.Neo

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For the last few weeks, I've been trying to create speculative planetary bodies. I know that sounds like a tall order; that's because it is.

Mainly I've been focused on a world with oceans, continents and tectonic activity, similar to Earth. It is quite a complex system to understand; plate boundaries transform over time, plates are constantly rifting, subducting, etc. Everything needs a consistent history.

Eventually, I felt like subducting my head through my desk...

So I decided to drop everything that I was doing (an example of why I'm awesome at setting a goal and completing it) and decided to make a Moon or Mercury-like world instead.

It sounded so simple at the time. For good reason; there's no tectonic activity on the Moon, and volcanic activity seems fairly limited (at least in comparison to Mars). The major features on the surface are formed by impact events- simple excavations of varying size, randomly distributed across the surface, layered over eachother in billions of years of bombardment.

So the method of creating such a world dawned on me; first create a greyscale heightmap of the object in question, by layering 'craters' (variations in shade, representing variations in altitude) of varying size over the image, guided by random points (to be generated by a random noise function or similar). After a specific set of iterations (representing the early history of the planet, when impacts would have been common), the average size of the craters would be reduced. In addition, throughout the process alterations would be made to account for phenomena such as volcanic eruptions and general wearing-down of features due to general [ame="http://en.wikipedia.org/wiki/Impact_gardening"]impact gardening[/ame].

Finally, a visual map of the object would be completed- albedo and colour features- based on factors such as craters (which turn up fresh regolith and create visually impressive ray systems) and old lava fields (like lunar maria).

I did not pay much concern to the issue of polar distortion due to the map projection. There are however methods to rectify this issue.

The problem I encountered, of course, is that image editors do not quite work in the same way as planets. Problem one is that using a specific image editing tool (primarily the dodge/burn tool, but also the normal 'paintbrush' tool at non-total opacity) when creating overlapping craters.

A common phenomenon is a younger crater superpositioned over an older one. The depths of each crater can be roughly similar, and the rim of the younger crater is above the floor of the older one, disrupting the outline of the older crater.

In my case, however, overlapping two 'craters' creates a lens-shaped darker area (which would represent a 'depression') between the two- this is a feature completely antithetical to reality.



Another paintbrush-tool-method (forgive my terminology; the proper terms confuse me), which (as far as I can understand) 'pastes' an image onto the picture, creates a crater-crater relationship quite similar to that in reality, but produces a new fatal flaw; since the same image is added with every brush 'stroke', every crater is the same depth, regardless of the altitude of the area it impacted, or the size of the crater in question! This too, of course, is antithetical to reality.



Here is a WIP heightmap in all of its unglory;



I'm not sure how to progress now. Undoubtedly my method is simplistic, and there are clearly certain aspects of lunar or mercurian geology that I'm missing- like rille, scarps, volcanic domes, etc, or the effects of distributions of elements and minerals on colouration and albedo. But I can't move on to focus on those things if I can't get the basic features of lunar-like geology right- and those features are impact craters and basins.
 
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spaceranger

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I suggest checking out Wilbur http://www.ridgenet.net/~jslayton/software.html

It's a free painter-like heightfield/image editor that supports various file formats and map projections. There's also a terrain-specific tool set.

Cool project, enjoy!

---------- Post added at 07:16 PM ---------- Previous post was at 07:11 PM ----------

I also suggest checking out the free version of World Machine World Machine Basic for a wealth of inspiration on mathematical terrain map processing.

For example, one method that is very useful for producing real-looking terrain is using lateral warp/displacement on the height field surface.
 

csanders

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You might want to try and use something like "overlay."

If you have an "overlay" layer, any color darker than middle grey will darken the image, any color brighter than middle grey will brighten it.

Example crater: ridges are bright - higher elevation, inner crater is darker - lower elevation.


Used with overlay:
 

T.Neo

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It's a free painter-like heightfield/image editor that supports various file formats and map projections. There's also a terrain-specific tool set.

Nice software, but looks like it'll need a lot of tinkering to get something that looks like a lunar surface (programs that generate mathematical terrains generally do not create something similar to the crater-pocked surface). The default tool-tips also seem to face similar problems to those I've found in GIMP;



If you have an "overlay" layer, any color darker than middle grey will darken the image, any color brighter than middle grey will brighten it.

Perhaps I'm missing something here, but wouldn't that require a new layer for every crater? A planet might have hundreds or even thousands of craters present at reasonable resolutions; I'd imagine this would simply be too time-consuming.
 
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csanders

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I'm curious. How are you going about making this?

Are you writing a program that calculates the images?

Are you making images in an editor (gimp), then placing them in the editor?
 

T.Neo

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Are you making images in an editor (gimp), then placing them in the editor?

I'm attempting to create the images 'manually' in GIMP, but am seeking a method by which to allow this process. Some kind of script to perform the task manually would be a great improvement, but is unfortunately beyond my skill level at the moment, so it is left as a task for my future self...
 
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