thirdparty/learning3d/utils/model_common_utils.py

import torch

def knn(x, k, add_one_to_k=False):
    if add_one_to_k: k = k + 1
    inner = -2 * torch.matmul(x.transpose(2, 1).contiguous(), x)
    xx = torch.sum(x**2, dim=1, keepdim=True)
    pairwise_distance = -xx - inner - xx.transpose(2, 1).contiguous()
    idx = pairwise_distance.topk(k=k, dim=-1)[1]  # (batch_size, num_points, k)
    return idx

def pc_normalize(pc):
    l = pc.shape[0]
    centroid = np.mean(pc, axis=0)
    pc = pc - centroid
    m = np.max(np.sqrt(np.sum(pc**2, axis=1)))
    pc = pc / m
    return pc

def square_distance(src, dst):
    """
    Calculate Euclid distance between each two points.
    src^T * dst = xn * xm + yn * ym + zn * zm；
    sum(src^2, dim=-1) = xn*xn + yn*yn + zn*zn;
    sum(dst^2, dim=-1) = xm*xm + ym*ym + zm*zm;
    dist = (xn - xm)^2 + (yn - ym)^2 + (zn - zm)^2
         = sum(src**2,dim=-1)+sum(dst**2,dim=-1)-2*src^T*dst
    Input:
        src: source points, [B, N, C]
        dst: target points, [B, M, C]
    Output:
        dist: per-point square distance, [B, N, M]
    """
    B, N, _ = src.shape
    _, M, _ = dst.shape
    dist = -2 * torch.matmul(src, dst.permute(0, 2, 1))
    dist += torch.sum(src ** 2, -1).view(B, N, 1)
    dist += torch.sum(dst ** 2, -1).view(B, 1, M)
    return dist

def index_points(points, idx):
    """
    Input:
        points: input points data, [B, N, C]
        idx: sample index data, [B, S]
    Return:
        new_points:, indexed points data, [B, S, C]
    """
    device = points.device
    B = points.shape[0]
    view_shape = list(idx.shape)
    view_shape[1:] = [1] * (len(view_shape) - 1)
    repeat_shape = list(idx.shape)
    repeat_shape[0] = 1
    batch_indices = torch.arange(B, dtype=torch.long).to(device).view(view_shape).repeat(repeat_shape)
    new_points = points[batch_indices, idx, :]
    return new_points

def farthest_point_sample(xyz, npoint, start_with_first_point=False):
    """
    Input:
        xyz: pointcloud data, [B, N, C]
        npoint: number of samples
    Return:
        centroids: sampled pointcloud index, [B, npoint]
    """
    device = xyz.device
    B, N, C = xyz.shape
    centroids = torch.zeros(B, npoint, dtype=torch.long).to(device)
    distance = torch.ones(B, N).to(device) * 1e10
    if not start_with_first_point:
        farthest = torch.randint(0, N, (B,), dtype=torch.long).to(device)
    else:
        farthest = torch.randint(0, N, (B,), dtype=torch.long).to(device) * 0
    batch_indices = torch.arange(B, dtype=torch.long).to(device)
    for i in range(npoint):
        centroids[:, i] = farthest
        centroid = xyz[batch_indices, farthest, :].view(B, 1, 3)
        dist = torch.sum((xyz - centroid) ** 2, -1)
        mask = dist < distance
        distance[mask] = dist[mask]
        farthest = torch.max(distance, -1)[1]
    return centroids

def knn_point(k, pos1, pos2):
    '''
    Input:
        k: int32, number of k in k-nn search
        pos1: (batch_size, ndataset, c) float32 array, input points
        pos2: (batch_size, npoint, c) float32 array, query points
    Output:
        val: (batch_size, npoint, k) float32 array, L2 distances
        idx: (batch_size, npoint, k) int32 array, indices to input points
    '''
    B, N, C = pos1.shape
    M = pos2.shape[1]
    pos1 = pos1.view(B,1,N,-1).repeat(1,M,1,1)
    pos2 = pos2.view(B,M,1,-1).repeat(1,1,N,1)
    dist = torch.sum(-(pos1-pos2)**2,-1)
    val,idx = dist.topk(k=k,dim = -1)
    return torch.sqrt(-val), idx

def query_ball_point(radius, nsample, xyz, new_xyz, get_cnt=False):
    """
    Input:
        radius: local region radius
        nsample: max sample number in local region
        xyz: all points, [B, N, C]
        new_xyz: query points, [B, S, C]
    Return:
        group_idx: grouped points index, [B, S, nsample]
    """
    device = xyz.device
    B, N, C = xyz.shape
    _, S, _ = new_xyz.shape
    group_idx = torch.arange(N, dtype=torch.long).to(device).view(1, 1, N).repeat([B, S, 1])
    sqrdists = square_distance(new_xyz, xyz)
    group_idx[sqrdists > radius ** 2] = N
    
    if get_cnt:
        mask = group_idx != N
        cnt = mask.sum(dim=-1)

    group_idx = group_idx.sort(dim=-1)[0][:, :, :nsample]
    group_first = group_idx[:, :, 0].view(B, S, 1).repeat([1, 1, nsample])
    mask = group_idx == N
    group_idx[mask] = group_first[mask]
    if get_cnt:
        return group_idx, cnt
    else:
        return group_idx

def get_graph_feature(x, k=20, device=None):
    # x = x.squeeze()
    x = x.view(*x.size()[:3])
    idx = knn(x, k=k)  # (batch_size, num_points, k)
    batch_size, num_points, _ = idx.size()

    if device is None:
        device = 'cuda' if torch.cuda.is_available() else 'cpu'
    
    idx_base = torch.arange(0, batch_size, device=device).view(-1, 1, 1) * num_points

    idx = idx + idx_base

    idx = idx.view(-1)

    _, num_dims, _ = x.size()

    x = x.transpose(2, 1).contiguous()  # (batch_size, num_points, num_dims)  -> (batch_size*num_points, num_dims) #   batch_size * num_points * k + range(0, batch_size*num_points)
    feature = x.view(batch_size * num_points, -1)[idx, :]
    feature = feature.view(batch_size, num_points, k, num_dims)
    x = x.view(batch_size, num_points, 1, num_dims).repeat(1, 1, k, 1)

    feature = torch.cat((feature, x), dim=3).permute(0, 3, 1, 2)

    return feature