core/modules/embed.py

# -*- coding: utf-8 -*-
# @Organization  : Tongyi Lab, Alibaba
# @Author        : Lingteng Qiu
# @Email         : 220019047@link.cuhk.edu.cn
# @Time          : 2025-08-31 10:02:15
# @Function      : Point embedding (positional encoding)

import torch
import torch.nn as nn


class PointEmbed(nn.Module):
    def __init__(self, hidden_dim=48, dim=128):
        super().__init__()

        assert hidden_dim % 6 == 0

        self.embedding_dim = hidden_dim
        e = torch.pow(2, torch.arange(self.embedding_dim // 6)).float() * np.pi
        e = torch.stack(
            [
                torch.cat(
                    [
                        e,
                        torch.zeros(self.embedding_dim // 6),
                        torch.zeros(self.embedding_dim // 6),
                    ]
                ),
                torch.cat(
                    [
                        torch.zeros(self.embedding_dim // 6),
                        e,
                        torch.zeros(self.embedding_dim // 6),
                    ]
                ),
                torch.cat(
                    [
                        torch.zeros(self.embedding_dim // 6),
                        torch.zeros(self.embedding_dim // 6),
                        e,
                    ]
                ),
            ]
        )

        self.register_buffer("basis", e)  # 3 x 16

        self.mlp = nn.Linear(self.embedding_dim + 3, dim)
        self.norm = nn.LayerNorm(dim)

    @staticmethod
    def embed(input, basis):
        projections = torch.einsum("bnd,de->bne", input, basis)
        embeddings = torch.cat([projections.sin(), projections.cos()], dim=2)

        return embeddings

    def forward(self, input):
        # input: B x N x 3
        embed = self.mlp(
            torch.cat([self.embed(input, self.basis), input], dim=2)
        )  # B x N x C
        embed = self.norm(embed)
        return embed