how to use czm_inverseViewProjection matrix?

CesiumJS
1

In my post precessing shader code，I want to get the screen point to world coordinates. I found "AutomaticUniforms.js" have a "czm_inverseViewProjection" variable，and document say:" It's An automatic GLSL uniform representing a 4x4 view-projection transformation matrix that transforms clip coordinates to world coordinates." So in the post pressing fragment Shader, I use code like this:

float depth = texture2D(depthTexture, v_textureCoordinates).r;
vec2 xy = vec2((depthTexture.x * 2.0 - 1.0), ((1.0 - depthTexture.y) * 2.0 - 1.0));
vec4 posInWorld = czm_inverseViewProjection * vec4(xy, depth, 1.0);
posInWorld = posInWorld / posInWorld.w;

But when I check the variable "posInWold", that seem not equal to the point world coordinates？
what's problem？

2

You can get the position in eye coordinates by applying czm_inverseProjection, then convert it to world coordinates with something like the following:

vec4 worldCoordinate4 = czm_inverseView * eyeCoordinate;

vec3 worldCoordinate = worldCoordinate4.xyz / worldCoordinate4.w;

``

Thanks!

Gabby

3

Thanks your help
But in "Apps/Sandcastle/index.html?src=3D%20Tiles%20Feature%20Picking.html" demo. I write post processing shader code like this:

void main(void)
{
    vec4 finalColor = texture2D(colorTexture, v_textureCoordinates);

    // get position clip coordinates
    vec2 uv = vec2(v_textureCoordinates);
    float depth = czm_readDepth(depthTexture, uv);
    vec2 xy = vec2((uv.x * 2.0 - 1.0), ((1.0 - uv.y) * 2.0 - 1.0));

    // get position in eye coordinates
    vec4 eyeCoordinate = czm_inverseProjection * vec4(xy, depth, 1.0);
    eyeCoordinate = eyeCoordinate / eyeCoordinate.w;

    // get position in world coordinates
    vec4 worldCoordinate4 = czm_inverseView * eyeCoordinate;
    vec3 worldCoordinate = worldCoordinate4.xyz / worldCoordinate4.w;
    
    // use ellipsoid equation to test the position is on ellipsoid surface?
    vec3 radii = vec3(6378137.0, 6378137.0, 6356752.314245);
    vec3 inverseRadii = vec3(1.0 / radii.x, 1.0 / radii.y, 1.0 / radii.z);
    vec3 scaled = inverseRadii * worldCoordinate;
    float one = dot(scaled, scaled);
    
    if (one >= 1.0)
    {// Isn't on ellipsoid surface, draw original color
        gl_FragColor = finalColor;
    }else
    {// On ellipsoid surface, draw red color
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n\
    }
}

I want just show 3D build model and draw red to earth surface，but the picture isn't right. Do your have any suggest?

4

Are you using terrain? Terrain won’t match the shape of the WSG84 ellipsoid exactly.