pointnet++代码逐行解析（四）——— provider
继续巩固PointNet++代码的实现这篇博客，把代码逐行注释一遍！
pointnet++的所有代码和数据集都在github上，Pytorch代码：https://github.com/yanx27/Pointnet2_pytorch
深度学习中数据预处理provider.py部分的python代码注释如下：
import numpy as np
# 归一化batch_data,使用以centroid为中心的块的坐标
def normalize_data(batch_data):
""" Normalize the batch data, use coordinates of the block centered at origin,
Input:
BxNxC array
Output:
BxNxC array
"""
B, N, C = batch_data.shape
normal_data = np.zeros((B, N, C))
for b in range(B):
pc = batch_data[b]
centroid = np.mean(pc, axis=0)
pc = pc - centroid
m = np.max(np.sqrt(np.sum(pc ** 2, axis=1)))
pc = pc / m
normal_data[b] = pc
return normal_data
# 打乱数据（有相应标签）
def shuffle_data(data, labels):
""" Shuffle data and labels.
Input:
data: B,N,... numpy array
label: B,... numpy array
Return:
shuffled data, label and shuffle indices
"""
# arange创建等差数列，0到最大值，也就是labels的编号
idx = np.arange(len(labels))
# 随机打乱idx
np.random.shuffle(idx)
return data[idx, ...], labels[idx], idx
# 打乱每个点云中的点顺序-用于更改FPS行为。对整个batch使用想用的打乱索引|idx
def shuffle_points(batch_data):
""" Shuffle orders of points in each point cloud -- changes FPS behavior.
Use the same shuffling idx for the entire batch.
Input:
BxNxC array
Output:
BxNxC array
"""
idx = np.arange(batch_data.shape[1])
np.random.shuffle(idx)
return batch_data[:,idx,:]
# 随机旋转点云进行数据集增广；每个形状沿向上方向旋转
def rotate_point_cloud(batch_data):
""" Randomly rotate the point clouds to augument the dataset
rotation is per shape based along up direction
Input:
BxNx3 array, original batch of point clouds
Return:
BxNx3 array, rotated batch of point clouds
"""
# 根据batch_data的矩阵结构，构造一个元素都是0的矩阵
rotated_data = np.zeros(batch_data.shape, dtype=np.float32)
for k in range(batch_data.shape[0]):
# 产生0-1之间的随机数，乘以2*np.pi，得到一个角度
rotation_angle = np.random.uniform() * 2 * np.pi
# 求此角度的cos和sin
cosval = np.cos(rotation_angle)
sinval = np.sin(rotation_angle)
# 然后组成一个3*3的旋转矩阵
rotation_matrix = np.array([[cosval, 0, sinval],
[0, 1, 0],
[-sinval, 0, cosval]])
# 一个shape_pc内是把batch_data切成多个3元素数组
shape_pc = batch_data[k, ...]
# 旋转点云数据：乘向上旋转矩阵
rotated_data[k, ...] = np.dot(shape_pc.reshape((-1, 3)), rotation_matrix)
return rotated_data
#沿着z轴旋转点云做数据增强
def rotate_point_cloud_z(batch_data):
""" Randomly rotate the point clouds to augument the dataset
rotation is per shape based along up direction
Input:
BxNx3 array, original batch of point clouds
Return:
BxNx3 array, rotated batch of point clouds
"""
rotated_data = np.zeros(batch_data.shape, dtype=np.float32)
for k in range(batch_data.shape[0]):
rotation_angle = np.random.uniform() * 2 * np.pi
cosval = np.cos(rotation_angle)
sinval = np.sin(rotation_angle)
rotation_matrix = np.array([[cosval, sinval, 0],
[-sinval, cosval, 0],
[0, 0, 1]])
shape_pc = batch_data[k, ...]
rotated_data[k, ...] = np.dot(shape_pc.reshape((-1, 3)), rotation_matrix)
return rotated_data
# 旋转具有法向量点云做数据增强
def rotate_point_cloud_with_normal(batch_xyz_normal):
''' Randomly rotate XYZ, normal point cloud.
Input:
batch_xyz_normal: B,N,6, first three channels are XYZ, last 3 all normal
Output:
B,N,6, rotated XYZ, normal point cloud
'''
for k in range(batch_xyz_normal.shape[0]):
rotation_angle = np.random.uniform() * 2 * np.pi
cosval = np.cos(rotation_angle)
sinval = np.sin(rotation_angle)
rotation_matrix = np.array([[cosval, 0, sinval],
[0, 1, 0],
[-sinval, 0, cosval]])
shape_pc = batch_xyz_normal[k,:,0:3]
shape_normal = batch_xyz_normal[k,:,3:6]
batch_xyz_normal[k,:,0:3] = np.dot(shape_pc.reshape((-1, 3)), rotation_matrix)
batch_xyz_normal[k,:,3:6] = np.dot(shape_normal.reshape((-1, 3)), rotation_matrix)
return batch_xyz_normal
#通过小的旋转随机扰动点云
def rotate_perturbation_point_cloud_with_normal(batch_data, angle_sigma=0.06, angle_clip=0.18):
""" Randomly perturb the point clouds by small rotations
Input:
BxNx6 array, original batch of point clouds and point normals
Return:
BxNx3 array, rotated batch of point clouds
"""
rotated_data = np.zeros(batch_data.shape, dtype=np.float32)
for k in range(batch_data.shape[0]):
angles = np.clip(angle_sigma*np.random.randn(3), -angle_clip, angle_clip)
Rx = np.array([[1,0,0],
[0,np.cos(angles[0]),-np.sin(angles[0])],
[0,np.sin(angles[0]),np.cos(angles[0])]])
Ry = np.array([[np.cos(angles[1]),0,np.sin(angles[1])],
[0,1,0],
[-np.sin(angles[1]),0,np.cos(angles[1])]])
Rz = np.array([[np.cos(angles[2]),-np.sin(angles[2]),0],
[np.sin(angles[2]),np.cos(angles[2]),0],
[0,0,1]])
R = np.dot(Rz, np.dot(Ry,Rx))
shape_pc = batch_data[k,:,0:3]
shape_normal = batch_data[k,:,3:6]
rotated_data[k,:,0:3] = np.dot(shape_pc.reshape((-1, 3)), R)
rotated_data[k,:,3:6] = np.dot(shape_normal.reshape((-1, 3)), R)
return rotated_data
# 将点云沿向上方向旋转一定角度
def rotate_point_cloud_by_angle(batch_data, rotation_angle):
""" Rotate the point cloud along up direction with certain angle.
Input:
BxNx3 array, original batch of point clouds
Return:
BxNx3 array, rotated batch of point clouds
"""
rotated_data = np.zeros(batch_data.shape, dtype=np.float32)
for k in range(batch_data.shape[0]):
#rotation_angle = np.random.uniform() * 2 * np.pi
cosval = np.cos(rotation_angle)
sinval = np.sin(rotation_angle)
rotation_matrix = np.array([[cosval, 0, sinval],
[0, 1, 0],
[-sinval, 0, cosval]])
shape_pc = batch_data[k,:,0:3]
rotated_data[k,:,0:3] = np.dot(shape_pc.reshape((-1, 3)), rotation_matrix)
return rotated_data
# 将具有法向量信息点云沿向上方向旋转一定角度
def rotate_point_cloud_by_angle_with_normal(batch_data, rotation_angle):
""" Rotate the point cloud along up direction with certain angle.
Input:
BxNx6 array, original batch of point clouds with normal
scalar, angle of rotation
Return:
BxNx6 array, rotated batch of point clouds iwth normal
"""
rotated_data = np.zeros(batch_data.shape, dtype=np.float32)
for k in range(batch_data.shape[0]):
#rotation_angle = np.random.uniform() * 2 * np.pi
cosval = np.cos(rotation_angle)
sinval = np.sin(rotation_angle)
rotation_matrix = np.array([[cosval, 0, sinval],
[0, 1, 0],
[-sinval, 0, cosval]])
shape_pc = batch_data[k,:,0:3]
shape_normal = batch_data[k,:,3:6]
rotated_data[k,:,0:3] = np.dot(shape_pc.reshape((-1, 3)), rotation_matrix)
rotated_data[k,:,3:6] = np.dot(shape_normal.reshape((-1,3)), rotation_matrix)
return rotated_data
#通过小的旋转随机扰动点云
def rotate_perturbation_point_cloud(batch_data, angle_sigma=0.06, angle_clip=0.18):
""" Randomly perturb the point clouds by small rotations
Input:
BxNx3 array, original batch of point clouds
Return:
BxNx3 array, rotated batch of point clouds
"""
rotated_data = np.zeros(batch_data.shape, dtype=np.float32)
for k in range(batch_data.shape[0]):
angles = np.clip(angle_sigma*np.random.randn(3), -angle_clip, angle_clip)
Rx = np.array([[1,0,0],
[0,np.cos(angles[0]),-np.sin(angles[0])],
[0,np.sin(angles[0]),np.cos(angles[0])]])
Ry = np.array([[np.cos(angles[1]),0,np.sin(angles[1])],
[0,1,0],
[-np.sin(angles[1]),0,np.cos(angles[1])]])
Rz = np.array([[np.cos(angles[2]),-np.sin(angles[2]),0],
[np.sin(angles[2]),np.cos(angles[2]),0],
[0,0,1]])
R = np.dot(Rz, np.dot(Ry,Rx))
shape_pc = batch_data[k, ...]
rotated_data[k, ...] = np.dot(shape_pc.reshape((-1, 3)), R)
return rotated_data
# 随机抖动点云。抖动是针对每个点
def jitter_point_cloud(batch_data, sigma=0.01, clip=0.05):
""" Randomly jitter points. jittering is per point.
Input:
BxNx3 array, original batch of point clouds
Return:
BxNx3 array, jittered batch of point clouds
"""
B, N, C = batch_data.shape
assert(clip > 0)
jittered_data = np.clip(sigma * np.random.randn(B, N, C), -1*clip, clip)
jittered_data += batch_data
return jittered_data
# 随机移位点云。移位是针对每个点云
def shift_point_cloud(batch_data, shift_range=0.1):
""" Randomly shift point cloud. Shift is per point cloud.
Input:
BxNx3 array, original batch of point clouds
Return:
BxNx3 array, shifted batch of point clouds
随机的平移（加或者减）
"""
B, N, C = batch_data.shape
shifts = np.random.uniform(-shift_range, shift_range, (B,3))
for batch_index in range(B):
batch_data[batch_index,:,:] += shifts[batch_index,:]
return batch_data
# 随机缩放点云，缩放是针对每个点云
def random_scale_point_cloud(batch_data, scale_low=0.8, scale_high=1.25):
""" Randomly scale the point cloud. Scale is per point cloud.
Input:
BxNx3 array, original batch of point clouds
Return:
BxNx3 array, scaled batch of point clouds
各个点的数值大小随机改变[0.8到1.125之间随机扩大或缩小]
"""
B, N, C = batch_data.shape
scales = np.random.uniform(scale_low, scale_high, B)
for batch_index in range(B):
batch_data[batch_index,:,:] *= scales[batch_index]
return batch_data
#随机丢弃点云中的点
def random_point_dropout(batch_pc, max_dropout_ratio=0.875):
''' batch_pc: BxNx3 对batch中每一个数据选取一部分点来去掉（用第一个点来替代）'''
for b in range(batch_pc.shape[0]):
dropout_ratio = np.random.random()*max_dropout_ratio # 0~0.875
drop_idx = np.where(np.random.random((batch_pc.shape[1]))<=dropout_ratio)[0]
if len(drop_idx)>0:
batch_pc[b,drop_idx,:] = batch_pc[b,0,:] # set to the first point
return batch_pc