three.js,glsl,webgl , Atmosphere Scattering for Earth from space and on the ground

## Question:

Tag: three.js,glsl,webgl

Please provide prompt how to make the atmosphere of the Earth so that it is visible from space and from the ground (as shown in the image)

a model of the earth:

``````Earth = new THREE.Mesh(new THREE.SphereGeometry(6700,32,32),ShaderMaterialEarth);
``````

model of the cosmos:

`````` cosmos= new THREE.Mesh(new THREE.SphereGeometry(50000,32,32),ShaderMaterialCosmos);
``````

and a light source:

``````sun = new THREE.DirectionalLight();
``````

where to start, just I do not know. Perhaps this should do `ShaderMaterialCosmos`, where to pass position of the camera, and calculate how should be painted pixel. But how?

I tried using the following but get zero vectors at the entrance of the fragment shader http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter16.html

``````vertexShader:

#define M_PI 3.1415926535897932384626433832795
const float ESun=1.0;
const float Kr = 0.0025;
const float Km = 0.0015;
const int nSamples = 2;
const float fSamples = 1.0;

const float fScaleDepth = 0.25;

varying vec2 vUv;
varying vec3 wPosition;
varying vec4 c0;
varying vec4 c1;
varying vec3 t0;

uniform vec3 v3CameraPos; ,    // The camera's current position
uniform vec3 v3LightDir;       // Direction vector to the light source
uniform vec3 v3InvWavelength;  // 1 / pow(wavelength, 4) for RGB
uniform float fCameraHeight;    // The camera's current height

const float fKrESun=Kr*ESun;           // Kr * ESun
const float fKmESun=Km*ESun;           // Km * ESun
const float fKr4PI=Kr*4.0*M_PI;            // Kr * 4 * PI
const float fKm4PI=Km*4.0*M_PI;           // Km * 4 * PI

const float fScaleOverScaleDepth= fScale / fScaleDepth;  // fScale / fScaleDepth

const float fInvScaleDepth=1.0/0.25;

float getNearIntersection(vec3 v3Pos, vec3 v3Ray, float fDistance2, float fRadius2)
{
float B = 2.0 * dot(v3Pos, v3Ray);
float C = fDistance2 - fRadius2;
float fDet = max(0.0, B*B - 4.0 * C);
return 0.5 * (-B - sqrt(fDet));
}

float scale(float fCos)
{
float x = 1.0 - fCos;
return fScaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));
}

void main() {

// Get the ray from the camera to the vertex and its length (which

// is the far point of the ray passing through the atmosphere)

vec3 v3Pos = position.xyz;
vec3 v3Ray = v3Pos - v3CameraPos;
float fFar = length(v3Ray);

v3Ray /= fFar;

// Calculate the closest intersection of the ray with

// the outer atmosphere (point A in Figure 16-3)

// Calculate the ray's start and end positions in the atmosphere,

// then calculate its scattering offset

vec3 v3Start = v3CameraPos + v3Ray * fNear;

fFar -= fNear;
float fStartAngle = dot(v3Ray, v3Start) / fOuterRadius;
float fStartDepth = exp(-fInvScaleDepth);
float fStartOffset = fStartDepth * scale(fStartAngle);

// Initialize the scattering loop variables

float fSampleLength = fFar / fSamples;
float fScaledLength = fSampleLength * fScale;
vec3 v3SampleRay = v3Ray * fSampleLength;
vec3 v3SamplePoint = v3Start + v3SampleRay * 0.5;

// Now loop through the sample points

vec3 v3FrontColor = vec3(0.0, 0.0, 0.0);
for(int i=0; i<nSamples; i++) {

float fHeight = length(v3SamplePoint);
float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fHeight));
float fLightAngle = dot(v3LightDir, v3SamplePoint) / fHeight;
float fCameraAngle = dot(v3Ray, v3SamplePoint) / fHeight;
float fScatter = (fStartOffset + fDepth * (scale(fLightAngle) * scale(fCameraAngle)));
vec3 v3Attenuate = exp(-fScatter *  (v3InvWavelength * fKr4PI + fKm4PI));
v3FrontColor += v3Attenuate * (fDepth * fScaledLength);
v3SamplePoint += v3SampleRay;

}

wPosition = (modelMatrix * vec4(position,1.0)).xyz;

c0.rgb = v3FrontColor * (v3InvWavelength * fKrESun);
c1.rgb = v3FrontColor * fKmESun;
t0 = v3CameraPos - v3Pos;

vUv = uv;

}

float getMiePhase(float fCos, float fCos2, float g, float g2){

return 1.5 * ((1.0 - g2) / (2.0 + g2)) * (1.0 + fCos2) / pow(1.0 + g2 - 2.0*g*fCos, 1.5);
}

// Rayleigh phase function
float getRayleighPhase(float fCos2){

//return 0.75 + 0.75 * fCos2;
return 0.75 * (2.0 + 0.5 * fCos2);

}

varying vec2 vUv;
varying vec3 wPosition;
varying vec4 c0;
varying vec4 c1;
varying vec3 t0;

uniform vec3 v3LightDir;
uniform float g;
uniform float g2;

void main() {

float fCos = dot(v3LightDir, t0) / length(t0);

float fCos2 = fCos * fCos;
gl_FragColor = getRayleighPhase(fCos2) * c0 +  getMiePhase(fCos, fCos2, g, g2) * c1;
gl_FragColor = c1;
}
``````

Chapter 16 of GPU Gem 2 has nice explanation and illustration for achieving your goal in real time.

Basically you need to perform ray casting through the atmosphere layer and evaluate the light scattering.

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