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I am a very experienced iOS Developer, but I am beginning my very first foray into 3D graphics (specifically with SceneKit). I'm trying to model a planet, and I have it working with a height map giving mountains and valleys to a simple sphere.

What I'm wondering now is, how might I have a variable sea level? As I understand it, a height map only affects how the image is rendered, but it doesn't actually change the geometry of the object, correct? So my first idea, to have a smaller sphere and scale it up or down relative to the planet so that it shows through in the lower-elevation areas, wouldn't work?

If that's the case, how else might I approach this? I'd love a code sample if it's simple or ready-made, but mostly I'm just looking for a conceptual answer that I can go off and implement. How might I take a height-mapped planet surface, and have an adjustable sea level that fills in the lower-elevation areas first? For simplicity, I'm treating sea level as purely altitude-based (i.e. I don't need to factor in dams or obstacles, and maintaining a consistent volume of water isn't important).

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3 Answers 3

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You should be able to animate the height using u_time in your shader. Example usage of u_time code in Xcode project download here - https://developer.apple.com/library/mac/samplecode/SceneKit_Slides_WWDC2013/Introduction/Intro.html (compiles to slide show, use -> key to goto slide 40-something)

Can you help me out? I've been trying to do a height map with SceneKit's SCNShaderModifierEntryPointGeometry and can't seem to get my (UIImage*)heightMap passed to a sampler2D variable in the shaderModifier. How are you passing your image? Thanks in advance.

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What you explain sounds reasonable. Generate a smaller sphere with the radius set for an appropriate sea level.

Alternativly generate a sphere and alter its scale. This'd be quicker than regenerating a new one.

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You need a 3d noise function (perlin,simplex,..). Call it f(x,y,z). Usualy this function returns a 0..1 float value. You simply decide your sea level float k in 0..1 and :

Foreach point of the sphere

If f(x,y,z) < k 

 k is your heigth in that point

Else

 f(x,y,z) is your heigth in that point
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    \$\begingroup\$ This is good info, but I'm looking for how to execute the sea level, rather than calculate it. As in, would it be a second image layer, like a normal map layer on the sphere? Should it be a second overlapping sphere, resizing in and out? Is there a way to adjust the height map dynamically to fit sea level? That sort of thing. What processes can can be used to create this effect? \$\endgroup\$
    – Nerrolken
    Commented Aug 12, 2015 at 15:38

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