# open3d.ml.torch.ops.build_spatial_hash_table¶

open3d.ml.torch.ops.build_spatial_hash_table(points, radius, points_row_splits, hash_table_size_factor, max_hash_table_size=33554432)

Creates a spatial hash table meant as input for fixed_radius_search

The following example shows how build_spatial_hash_table and fixed_radius_search are used together:

import open3d.ml.tf as ml3d

points = [
[0.1,0.1,0.1],
[0.5,0.5,0.5],
[1.7,1.7,1.7],
[1.8,1.8,1.8],
[0.3,2.4,1.4]]

queries = [
[1.0,1.0,1.0],
[0.5,2.0,2.0],
[0.5,2.1,2.1],
]

# build the spatial hash table for fixex_radius_search
table = ml3d.ops.build_spatial_hash_table(points,
points_row_splits=torch.LongTensor([0,5]),
hash_table_size_factor=1/32)

# now run the fixed radius search
queries,
points_row_splits=torch.LongTensor([0,5]),
queries_row_splits=torch.LongTensor([0,3]),
**table._asdict())
# returns neighbors_index      = [1, 4, 4]
#         neighbors_row_splits = [0, 1, 2, 3]
#         neighbors_distance   = []

# or with pytorch
import torch
import open3d.ml.torch as ml3d

points = torch.Tensor([
[0.1,0.1,0.1],
[0.5,0.5,0.5],
[1.7,1.7,1.7],
[1.8,1.8,1.8],
[0.3,2.4,1.4]])

queries = torch.Tensor([
[1.0,1.0,1.0],
[0.5,2.0,2.0],
[0.5,2.1,2.1],
])

# build the spatial hash table for fixex_radius_search
table = ml3d.ops.build_spatial_hash_table(points,
points_row_splits=torch.LongTensor([0,5]),
hash_table_size_factor=1/32)

# now run the fixed radius search
queries,
points_row_splits=torch.LongTensor([0,5]),
queries_row_splits=torch.LongTensor([0,3]),
**table._asdict())
# returns neighbors_index      = [1, 4, 4]
#         neighbors_row_splits = [0, 1, 2, 3]
#         neighbors_distance   = []


max_hash_table_size: The maximum hash table size.

points: The 3D positions of the input points.

radius: A scalar which defines the spatial cell size of the hash table.

points_row_splits: 1D vector with the row splits information if points is

batched. This vector is [0, num_points] if there is only 1 batch item.

hash_table_size_factor:

The size of the hash table as a factor of the number of input points.

hash_table_index: Stores the values of the hash table, which are the indices of

the points. The start and end of each cell is defined by hash_table_cell_splits.

hash_table_cell_splits: Defines the start and end of each hash table cell within

a hash table.

hash_table_splits: Defines the start and end of each hash table in the

hash_table_cell_splits array. If the batch size is 1 then there is only one hash table and this vector is [0, number of cells].