float volumecubicsample(<geometry>geometry, int primnum, vector pos)
float volumecubicsample(<geometry>geometry, string volumename, vector pos)
float volumecubicsample(<geometry>geometry, int primnum, vector pos, vector &grad)
float volumecubicsample(<geometry>geometry, string volumename, vector pos, vector &grad)
float volumecubicsample(<geometry>geometry, int primnum, vector pos, vector &grad, matrix3 &hess)
float volumecubicsample(<geometry>geometry, string volumename, vector pos, vector &grad, matrix3 &hess)
<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 and hess arguments return the gradient or the hessian of this sampling function which can be computed at the same time as the value.
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.
Example of interpolation of one and two dimensional data using volumecubicsample. The visualized normal is computed using the grad parameter.
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}; vector grad; matrix3 hess; float val1 = volumecubicsample(0, "density", P, grad, hess); vector u = {0.1, 0.01, 0.001}; float val2 = volumecubicsample(0, "density", P + u); // By Taylor expansion we have: // `val1 + dot(u, grad)` is approximately equal to `val2` // And the second order approximation: // `val1 + (u, grad) + 0.5 * dot(u, u*hess)` // is appriximately equal to `val2`
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