Understanding Latitude Space

This tutorial came about from a discussion on the Mojobeta email list about the new latitude space coordinates available in version 1.1 of MojoWorld. Mo never did answer my question. I'll throw in a digression on what that was all about at the end of the tutorial.

Doc Mojo's text has been spell-checked and colored pink. (Well, no spell-checker was going to be able to fix it when Mo typed "know" and he really meant "now"!) My text was typed right the first time ;) and is colored dark grey like all the rest of my text here on my soapbox.

Okay, first we need to know the units we're working in: In World Space, the planet has a radius of 6 million meters. Latitude varies from -90 degrees to 90 degrees. Keeping this in mind is key!

  1. Create a new planet. Move the camera up to where you can see the whole planet, from above the equator (Lat. 0 0 N, Long. unimportant), at high noon. Set the atmosphere to None.

    I always open the camera edit dialog at this point and make a new camera here and call it 'spacecam'. I find it invaluable to have a camera out in space that I can quickly switch to when making changes that'll affect things on a global scale. Don't forget to pick a camera other than 'spacecam' when it comes time to go exploring, though, otherwise you'll lose the outer space view.

    [Note: At this point you may want to check to make sure that your sunlight is white (1.0, 1.0, 1.0) and that your ambient light is zero. Ambient light lives in the Object List in MojoWorld.]

  2. Create a new material for the terrain.

    Actually, all you have to do is edit the default green material that's already applied to the planet.

  3. Create a new texture for the Diffuse component.

    Serious Mojonauts can skip this next obvious bit:

    Change the Diffuse widget to Texture. This will open a new texture editor dialog. Select New Texture from the menu. Click the first ghosted T to enable the first texture leaf. Click the T again to open the texture leaf kickstand.

  4. Delete the Monofractal at the top of the kickstand (set it to None).

    This was the crux of my un-answered question, but rather than confuse y'all now, I'll discuss it at the end.

  5. Change World Position (at the bottom of the kickstand) to Latitude. You should now have a planet that's white on top and black on the bottom (if North is up in your RTR window).

This is what the texture editor will look like at this point in the process. Your texture editor may show better names for the material and texture if you've been on top of naming things!

    Now comes the tricky part: remapping things into the proper values for the given coordinate system.

  1. Open the Ouput Control on the kickstand.

  2. Open the Input Curve. Set Min Input to -90.0 and Max Input to 90.0.

    Here you can set Min Input to 0 and set the 'Beyond Input' ddlb to 'Mirror' instead - if you want to have your planet be the same in the two hemispheres.

  3. In the Curve Editor Window, choose Add Point (the arrow-plus icon). Add a third knot (the first two being at the ends of the curves) in the middle of the curve.

  4. Change back to Move Point (the arrow icon). Click on all three points and rotate their slope handles so that they are horizontal.

  5. Move the left point to the top of the window (or just type in 1.0 in the Output field for that point, while it's selected).

  6. Select the middle point, and type in 0.0 in both Input and Output.

    This is what the curve editor will look like after setting it up according to Mo's directions. Set up this way, the curve editor can be used to provide different mappings of the gradient to either hemisphere of the planet.

  7. To make what's going on more clear (lighting at the poles being rather dim), make the black end of your Gradient red (1.0, 0.0, 0.0), and the white end green (0.0, 1.0, 0.0).

    You now have a planet that's red at the equator with a smooth gradation to hideous green poles. You may want to get a better view of the pole now. You can do this by aiming the camera up toward the North pole (by dragging the planet up in the RTR window, presuming "up" is North in your RTR window), and hitting "w" until the red line indicating the sun's orbit is at the top of the planet.

  8. Now comes the fun part: Fiddle with the Gradient until you get the climate bands you want. I like a fat white band for ice caps at the poles (with a grey margin for bare rocks), buff-colored sand at the equator (with a brick red margin), and various shades of green for the temperate zones in between. But do whatever you like!

    After this, you should have a planet that looks something like latitude_test.01.mjw. Now we need to add some fractal perturbation to the climate bands to make them look more realistic.

  9. Go to the middle kickstand item, Edit the Distortion, and change it from None to Monofractal. (You'll want to be more creative here later, choosing whatever fractal you please.)

  10. Now for the next remapping of units. Largest Feature Size here is, like the name implies, the size of the largest perturbation feature, as measured in terms of its extent across the planet surface. I recommend setting it to roughly the radius of the planet, 6,000,000, maybe half that, or even the diameter of the planet, 12,000,000. Nothing visible happens. We have to do one more remapping.

  11. What we're perturbing is the latitude, which varies between -90 and +90. Change Result Scale from 1.0 to 90.0 for fun. Whoa! Too much! How about 30. Maybe 20. Maybe only 10. Whatever you like.

  12. It's too soft, this perturbation. Change Roughness from 0.375 to 0.5. Hmm. "Add Roughness to taste." See latitude_test.02.mjw.

There you have it! You are now a Certified MojoWorld Latitude Master.

The Unanswered Question

Back in Step 4, Mo says to set the fractal to None. My original question was, "what sorts of Largest Feature Size and Result Scale values should one use on the fractal in the 'normal' slot (as opposed to the fractal in the 'distortion' slot)?"

Here's a simple planet that has been worked through this tutorial up to step 12. Instead of applying a nice gradient and then using a distortion fractal, I've left it red and hideous green and put a fractal in on the 'normal' slot. The LFS is 20 and the Result Scale is 200. It would seem that the LFS is degrees-of-latitude scaled, but I'm not sure what sort of units the Result Scale is using. When the Result Scale is dropped to around 30, the planet goes mostly red; above 90,000 and it's mostly green.

 

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