Question about two functions: ViewCalculator::getBlocksInImageViewRaycast() and checkBlocksInTruncationBand()

[gogojjh]

Hi, Thanks for your great works. I have two questions regarding details of NVblox:

Q1: Voxel block retrieval in the TSDF integration:

nvblox/nvblox/src/integrators/cuda/projective_tsdf_integrator.cu

Line 270 in 61d0f08

const std::vector<Index3D> block_indices =

Could you please check the correctest of my understanding: it seems that indices of all visible voxel blocks (traversed by the ray) are stored as the block_indices. The TSDF values and weights of voxels from these blocks will be updated, through TSDF values of voxels (purple one in the below figure) which are far away from the truncation are equal to the truncation_distance_m.

Q2: Reduce blocks in the color integration:

nvblox/nvblox/src/integrators/cuda/projective_color_integrator.cu

Line 300 in 61d0f08

if (std::abs(voxel.distance) <= truncation_distance_m) {

For the color integration, we are interested in voxels which are near surfaces. In other words, only these voxels should have colored. Thus, could you please explain why the critera of reducing blocks like this
if (std::abs(voxel.distance) <= truncation_distance_m)?

I think that the critera should be set as
if (std::abs(voxel.distance) < truncation_distance_m && std::abs(voxel.distance) > 0)
to keep voxels which are already observed before and near surfaces.

Thanks.

[alexmillane]

Thank you for the question and for your interest in nvblox.

Q1: You're absolutely correct! :)

Q2: I think that there's a typo in your condition, the second clause looks incorrect to me: std::abs(voxel.distance) > 0. I guess you mean std::abs(voxel.weight) > 0. That's actually a good idea. We'll put that in the next release.

Thank you for pointing that out.

[gogojjh]

Hi Alex,

Thanks for your reply.
Regarding the Q1, for the purpose of large-scale reconstruction, it seems that only green voxels are focused. Would it be possible for us to only store green voxels to avoid large memory footprint?

Thanks.