Veidrheim - Questions on Tectonics and Projections

[Ritterfeld]

Hey guys,

I am currently working on the planet my writting is taking place on. I have settled for continents and their shape and am currently in the process of figuring out plate tectonics and climate zones. These are the tectonics I have settled on for now. I would like some feedback and advice and I would like to check for mistakes, so if you guys spot anything impossible or implausible, please point that out to me. so I can fix it, so I can move on to climate zones.


Also there is another thing I need advice on. Since I only worked in 2d I have no idea on how to create proper projections. I know that the continents like I put them now, are not plausible taking into account distortion. My priority would be to have my continents UNDISTORTED on the globe (the same form they are now in 2d) and then make a proper projection for the 2d maps. Can anyone explain to me, how to do that?


Many thanks in advance!

Ritterfeld

[MrBragg]

As far as projection goes, the best software I've found is MMPS. It's command line only, but it's quite versatile and can convert from equirectangular to other projections and also the other direction and it's worked really well for me. It also doesn't seem to have a resolution limit, which might be useful since the image you posted is ~14k x 7k. Another option would be gprojector which is probably more user friendly but does have a resolution limit.

If you like the shape of your continents as they are, you could take the current shape of each one and say that that shape is how the continent looks in some locally minimally distorted projection (which will depend on continent size / shape / latitude / etc). You could then use MMPS to reproject that shape to equirectangular from the initial projection to get the correct distorted shape on an equirectangular map. If what I'm trying to say here doesn't make sense, feel free to ask me to clarify.

Finally, for tectonics, I'd really recommend gplates, plus the excellent tutorial on this site on how to use it. It takes some getting used to, but it's super helpful for visualizing if your plate motions make sense and for seeing what each type of plate interaction is.

[waldronate]

I have some really bad news for you: you can't keep the continents the way they are and also project them onto a sphere. The math doesn't allow it. Your tectonics also won't work as shown because the angles and distances will change radically when you reproject the map.

As MrBragg suggests, you might be able to reduce some of the distortions in certain areas by careful selection of a specific projection for each area that you care about and then pasting those together on a globe. However, what he didn't mention is that many of your areas are so large that they will get some significant distortion (angular, area, or both) no matter what you do. In cases like this, it's often best to paste things together to a "good enough" state and declare that the earlier cartographers just had some questionable data (this was very true for most early maps here on Earth).

If the red lines on your map are intended to be things like an equator and various tropic lines, then it looks like you started drawing things on a cylindrical grid for a projection akin to Mercator. If you had intended to use Mercator, it does have the nice feature that it will preserve the relative angles of your coastlines when you reproject it back to a globe, but the areas of those things will be radically changed. You'll also be missing the tops and bottoms of your world because Mercator is infinite in extent vertically.

The most important part of all of this, of course: "What Do You Want To Do With This Map?" If it's an aid for storytelling, then it probably doesn't need to be completely physically correct or even necessarily self-consistent. Being able to answer questions like "these parts are probably cold" and "this journey would take two months by land, but two weeks by sea" can often be sufficient for storytelling. Information about tectonics might help you answer questions like "these mountains would have good ores" and "these soils are old and sad", but the shapes are unlikely to matter too much unless you have a very long-term story or significant time travel. A rough map is sufficient for inspiration and reference, but doesn't need to be more than vaguely plausible for most folks.

I'll stop ranting now, because I tend to go down this pathway too often for everyone's good. Plausible can be done fairly quickly, but Correct is never done.

[Ritterfeld]

I know distortion cannot be avoided and I don't want to. What I would rather have is an undistorted globe and a distorted 2d map - basically the opposite of what I have now. I am absolutely fine with the continents being distorted on the map. I care for them having (more or less) the form as I drew them on the globe rather than the map. Since I am new to this kind of stuff, I have no way of telling, but is there no way of achieving this?

Yeah, I guess I could use these kind of "excuses" but if in any way avoidable, I would like not to. I'm willing to adjust plates afterwards. What I care about know is having an undistorted globe view and a distorted map view.

I have some really bad news for you: you can't keep the continents the way they are and also project them onto a sphere. The math doesn't allow it. Your tectonics also won't work as shown because the angles and distances will change radically when you reproject the map.

As MrBragg suggests, you might be able to reduce some of the distortions in certain areas by careful selection of a specific projection for each area that you care about and then pasting those together on a globe. However, what he didn't mention is that many of your areas are so large that they will get some significant distortion (angular, area, or both) no matter what you do. In cases like this, it's often best to paste things together to a "good enough" state and declare that the earlier cartographers just had some questionable data (this was very true for most early maps here on Earth).

Thanks to you MrBragg as well, I will definitely look into it

[Bindusara]

Hi

If you like the shape of your continents, just project one continent by one continent on a sphere (you cut the map around a continent, smash it on the sphere ;-) ). It will dicrease the deformation. The main impacts will be on your oceans and seas, and on your tectonical boundaries :you'll have to reconnect the lines

[waldronate]

As everyone so far has pointed out, you can project each continent individually (basically, you cut out each continent, declare that it's "correct" in form and pick a projection for that continent that will minimize distortion based on the size of the continent).

For best effect, you need to describe that map a little. My earlier guess was that the red lines represent something like parallels (equator, tropics, and so on). If that's true, then you have already decided on a map projection (or at least a projection family) because straight horizontal lines on the 2D map (assuming north up or down) means that your projection is something from the cylindrical projection family. The non-linear spacing and missing poles strongly suggest Mercator.

Taking that earlier map as a Mercator projection and pushing it to a globe gives a result like this:



The shapes are generally correct, but the sizes vary from what you original showed. The blue polar regions are parts that were missing from your original map. I generated the frames for this animation using some elderly software that I wrote a long time ago ( ReprojectImage from my web site to change Mercator to Equirectangular and Fractal Terrains from ProFantasy to generate the Orthographic frames ) and assembled it in Photoshop.

[Ritterfeld]

Taking that earlier map as a Mercator projection and pushing it to a globe gives a result like this:



The shapes are generally correct, but the sizes vary from what you original showed. The blue polar regions are parts that were missing from your original map. I generated the frames for this animation using some elderly software that I wrote a long time ago ( ReprojectImage from my web site to change Mercator to Equirectangular and Fractal Terrains from ProFantasy to generate the Orthographic frames ) and assembled it in Photoshop.

Wow! :O This is an mazing result, many thanks. I am completely new to 3d cartography - basically all I did until now was drawing stuff onto a piece of paper. For that matter, may I message you and ask you for some technical details etc.?

Many thanks, this issue is driving me crazy for a good two weeks now.

[waldronate]

You can message and ask for technical details or ask in public. The nice thing about discussing in public is that other people can benefit from the discussion as well.

There isn't really anything "3D" in that image: it's manipulation of 2D images via map projections.

[Ritterfeld]

You can message and ask for technical details or ask in public. The nice thing about discussing in public is that other people can benefit from the discussion as well.

There isn't really anything "3D" in that image: it's manipulation of 2D images via map projections.

Alright, I just thought that in proivate might be easier. As I said, I am entirely new to this area of world building. So, my first question would be which program I need to/I should use to project the continents individually. Also, do you have any reccomendation for good/beginner-friendly tutorials for this program?

Thanks in advance!

[waldronate]

I'm not going to be able to offer much in the way of links to tutorials, I'm afraid. It's been a very long time since I was a beginner and I figure that everyone should be able to use a search engine for basic software tutorials once you know the product names.


First, you need to decide how much of your globe is actually visible on the map that you initially showed (it doesn't have polar regions and you'll need to decide how large those regions are). You'll also need to determine what (if any) significance the red lines have.

Decide which continents you want work on. Doing every little continent and island may be more than you have patience for.

You'll need to pick map projections that will minimize distortions for each continent. https://desktop.arcgis.com/en/arcmap...projection.htm may be a good place to start.

Pick a center of projection for each continent. In this step, you're defining where on the globe your continent will go.

You'll need something that can reproject the chosen image to Equirectangular projection (Equirectangular is a common input format for many programs that can map things to globes). I generally recommend GDAL, but it's a bit intimidating because it's a purely command-line program. QGIS offers the same sort of features, but it can be a bit impenetrable if you're not familiar with GIS terms. As MrBragg suggested, MMPS should be able do this sort of thing as well (it looks like it has a fairly limited list of projections, but that might be good enough: I've never used MMPS). If you're not worried about pinpoint accuracy and are willing to live with a somewhat twitchy GUI and limited (4096) export resolution, ReprojectImage ( http://fracterra.com/ReprojectImage.zip ) might be workable for you.

And now we get to the fun part: chopping out the pieces. Use your chosen software package to import the base image, enter the projection and center of projection (keep the scale the same), and convert it to equirectangular. There will be a bunch of garbage in your Equirectangular export, but you'll be fixing that next. Repeat this conversion and export process for each continent.

Get out your favorite paint program. I recommend getting one that supports transparency and layers if you don't already have one. The GIMP is popular option if you don't already have one that you use regularly, but it can take some getting used to.

In the paint program, import each image that you exported from your projection program. Erase everything that's not associated with the continent of interest. You'll be forming a stack of layers that represent your world in the equirectangular projection. Each layer is one output from the projection program. After everything is done, you can export the flattened image, ready for input into your favorite globe-making software.


Another option to all of the reprojection stuff is to get a paint program that can draw onto a sphere and just redraw the map directly onto the sphere. Not a great option, but then you'd be able to easily control distortions yourself and possibly emphasize regions that are more important for your writing. Painting on the sphere directly also greatly simplifies getting plates and plate motions correct over the poles.