vector volumecubicsamplev(<geometry>geometry, int primnum, vector pos)
vector volumecubicsamplev(<geometry>geometry, string volumename, vector pos)
vector volumecubicsamplev(<geometry>geometry, int primnum, vector pos, matrix3 &grad)
vector volumecubicsamplev(<geometry>geometry, string volumename, vector pos, matrix3 &grad)
vector volumecubicsamplev(<geometry>geometry, int primnum, vector pos, matrix3 &grad, matrix3 &hessX, matrix3 &hessY, matrix3 &hessZ)
vector volumecubicsamplev(<geometry>geometry, string volumename, vector pos, matrix3 &grad, matrix3 &hessX, matrix3 &hessY, matrix3 &hessZ)
<geometry>
When running in the context of a node (such as a wrangle SOP), this argument can be an integer representing the input number (starting at 0) to read the geometry from.
Alternatively, the argument can be a string specifying a geometry file (for example, a .bgeo) to read from. When running inside Houdini, this can be an op:/path/to/sop reference.
Returns
The volume primitive’s sampled value at the given position. Values between voxels are evaluated with tri-cubic interpolation.
The grad is a matrix whose i-th column is the gradient of the i-th component of the volume.
Matrices hessX, hessY, hessZ are second derivatives of x, y and z component respectively.
Returns 0 if primnum or inputnum is out of range, the geometry is invalid, or the given primitive is not a volume or vdb primitive.
Examples ¶
Approximating a volume value at the point P + u using volume values at the point P.
vector P = {1.0, 2.0, 3.0}; matrix3 grad, hessX, hessY, hessZ; vector val1 = volumecubicsamplev(0, "vel", P, grad, hessX, hessY, hessZ)); vector u = {0.1, 0.01, 0.001}; vector val2 = volumecubicsamplev(0, "vel", P + u); // By Taylor expansion we have: // `val1 + u * grad` is approximately equal to `val2` // And the second order approximation: // `val1 + u * grad + 0.5 * set(dot(u, u*hessX), dot(u, u*hessY), dot(u, u*hessZ))` // is appriximately equal to `val2`
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