From 0ac6625d2d05fafe6b0b637540e97d90e54e3596 Mon Sep 17 00:00:00 2001
From: liyinhao <liyinhao@sensetime.com>
Date: Sun, 2 Aug 2020 11:27:01 +0800
Subject: [PATCH] Add centerpoint_rpn.

---
 mmdet3d/models/necks/centerpoint_fpn.py | 91 +++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 mmdet3d/models/necks/centerpoint_fpn.py

diff --git a/mmdet3d/models/necks/centerpoint_fpn.py b/mmdet3d/models/necks/centerpoint_fpn.py
new file mode 100644
index 0000000000..88c44c23d9
--- /dev/null
+++ b/mmdet3d/models/necks/centerpoint_fpn.py
@@ -0,0 +1,91 @@
+import numpy as np
+import torch
+from mmcv.cnn import (build_conv_layer, build_norm_layer, build_upsample_layer,
+                      constant_init, is_norm, kaiming_init)
+from torch import nn as nn
+
+from mmdet.models import NECKS
+
+
+@NECKS.register_module()
+class CenterPointFPN(nn.Module):
+    """FPN used in SECOND/PointPillars/PartA2/MVXNet.
+
+    Args:
+        in_channels (list[int]): Input channels of multi-scale feature maps.
+        out_channels (list[int]): Output channels of feature maps.
+        upsample_strides (list[int]): Strides used to upsample
+            the feature maps.
+        norm_cfg (dict): Config dict of normalization layers.
+        upsample_cfg (dict): Config dict of upsample layers.
+        conv_cfg (dict): Config dict of conv layers.
+    """
+
+    def __init__(self,
+                 in_channels=[128, 128, 256],
+                 out_channels=[256, 256, 256],
+                 upsample_strides=[1, 2, 4],
+                 norm_cfg=dict(type='BN', eps=1e-3, momentum=0.01),
+                 upsample_cfg=dict(type='deconv', bias=False),
+                 conv_cfg=dict(type='Conv2d', bias=False)):
+        # if for GroupNorm,
+        # cfg is dict(type='GN', num_groups=num_groups, eps=1e-3, affine=True)
+        super(CenterPointFPN, self).__init__()
+        assert len(out_channels) == len(upsample_strides) == len(in_channels)
+        self.in_channels = in_channels
+        self.out_channels = out_channels
+
+        deblocks = []
+        for i, out_channel in enumerate(out_channels):
+            stride = upsample_strides[i]
+            if stride > 1:
+                upsample_layer = build_upsample_layer(
+                    upsample_cfg,
+                    in_channels=in_channels[i],
+                    out_channels=out_channel,
+                    kernel_size=stride,
+                    stride=upsample_strides[i])
+                deblock = nn.Sequential(
+                    upsample_layer,
+                    build_norm_layer(norm_cfg, out_channel)[1],
+                    nn.ReLU(inplace=True))
+            else:
+                stride = np.round(1 / stride).astype(np.int64)
+                upsample_layer = build_conv_layer(
+                    conv_cfg,
+                    in_channels=in_channels[i],
+                    out_channels=out_channel,
+                    kernel_size=stride,
+                    stride=stride)
+                deblock = nn.Sequential(
+                    upsample_layer,
+                    build_norm_layer(norm_cfg, out_channel)[1],
+                    nn.ReLU(inplace=True))
+            deblocks.append(deblock)
+        self.deblocks = nn.ModuleList(deblocks)
+
+    def init_weights(self):
+        """Initialize weights of FPN."""
+        for m in self.modules():
+            if isinstance(m, nn.Conv2d):
+                kaiming_init(m)
+            elif is_norm(m):
+                constant_init(m, 1)
+
+    def forward(self, x):
+        """Forward function.
+
+        Args:
+            x (torch.Tensor): 4D Tensor in (N, C, H, W) shape.
+
+        Returns:
+            list[torch.Tensor]: Multi-level feature maps.
+        """
+        assert len(x) == len(self.in_channels)
+        ups = [deblock(x[i]) for i, deblock in enumerate(self.deblocks)]
+
+        if len(ups) > 1:
+            out = torch.cat(ups, dim=1)
+        else:
+            out = ups[0]
+        return out