some questions about coneParallelBackprojectorKernel_vox

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I mainly want to understand the reconstruction after converting cone beam to parallel beam in the backprojectors_VD.cu file. In the coneParallelBackprojectorKernel_vox function, I understand that backprojection weight does not need to be calculated in parallel beam backprojection, while it is required in cone beam geometry. However, I am not sure whether this backprojection weight is needed in the Cone Beam Parallel Backprojector. In the code:
`// Calculate backprojection weight-related parameters`
`const float v_denom = sqrtf(R * R - s * s) - (cos_phi * x + sin_phi * y);`
`const float v_denom_inv = 1.0f / v_denom;`
`const float backprojectionWeight = doWeight ? R : R*R * v_denom_inv;`

In the subsequent code, it is multiplied by sqrtf(1.0f + v_arg*v_arg):

`tex3D(g, s_arg, v_phi_x_first + k_offset * v_phi_x_step_A, L) * backprojectionWeight * sqrtf(1.0f + v_arg*v_arg);`

Could you recommend any papers or articles where I can refer to this backprojection weight?
Additionally, regarding const float asin_tau_over_R = asin(tau / R);, is this used for cone beam artifact correction?

Start in backprojectors_VD.cu at coneParallelBackprojectorKernel_vox and trace doWeight, v_denom, backprojectionWeight, and asin_tau_over_R. Compare those expressions with the reconstruction papers or articles requested in the issue. Done means documenting whether the weight applies to the cone-beam parallel backprojector and what asin_tau_over_R is used for.

Written by the indexing model from the issue text.