[CodeCamp] #50 Add module combination doc (#349)

* the file  to verify the installation

* "add module_combination"

* add module_combination

* modified module_combination.md

* modify module_combination.md

* fix module_combination.md

docs/zh_cn/advanced_guides/module_combination.md

@@ -171,3 +171,110 @@ model = dict(
             beta=6)
     ))
 ```
+
+## Backbone + Neck + HeadModule 的组合替换
+
+### 1. YOLOv5 Backbone 替换
+
+(1) 假设想将 `RTMDet backbone + yolov5 neck + yolov5 head` 作为 `YOLOv5` 的完整网络，则配置文件如下：
+
+```python
+_base_ = './yolov5_s-v61_syncbn_8xb16-300e_coco.py'
+
+widen_factor = 0.5
+deepen_factor = 0.33
+
+model = dict(
+    backbone=dict(
+        _delete_=True,
+        type='CSPNeXt',
+        arch='P5',
+        expand_ratio=0.5,
+        deepen_factor=deepen_factor,
+        widen_factor=widen_factor,
+        channel_attention=True,
+        norm_cfg=dict(type='BN'),
+        act_cfg=dict(type='SiLU', inplace=True))
+)
+```
+
+(2)  `YOLOv6EfficientRep backbone + yolov5 neck + yolov5 head` 作为 `YOLOv5` 的完整网络，则配置文件如下：
+
+```python
+_base_ = './yolov5_s-v61_syncbn_8xb16-300e_coco.py'
+
+model = dict(
+    backbone=dict(
+        type='YOLOv6EfficientRep',
+        norm_cfg=dict(type='BN', momentum=0.03, eps=0.001),
+        act_cfg=dict(type='ReLU', inplace=True))
+)
+```
+
+### 2. YOLOv5 Neck 替换
+
+(1) 假设想将 `yolov5 backbone + yolov6 neck + yolov5 head` 作为 `YOLOv5` 的完整网络，则配置文件如下：
+
+```python
+_base_ = './yolov5_s-v61_syncbn_8xb16-300e_coco.py'
+
+model = dict(
+    neck = dict(
+        type = 'YOLOv6RepPAFPN',
+        in_channels = [256, 512, 1024],
+        out_channels = [128, 256, 512], # 注意 YOLOv6RepPAFPN 的输出通道是[128, 256, 512]
+        num_csp_blocks = 12,
+        act_cfg = dict(type='ReLU', inplace = True),
+    ),
+    bbox_head = dict(
+        head_module = dict(
+            in_channels = [128, 256, 512])) # head 部分输入通道要做相应更改
+)
+```
+
+(2) 假设想将 `yolov5 backbone + yolov7 neck + yolov5 head` 作为 `YOLOv5` 的完整网络，则配置文件如下：
+
+```python
+_base_ = './yolov5_s-v61_syncbn_8xb16-300e_coco.py'
+
+deepen_factor = _base_.deepen_factor
+widen_factor = _base_.widen_factor
+
+model = dict(
+    neck = dict(
+        _delete_=True, # 将 _base_ 中关于 neck 的字段删除
+        type = 'YOLOv7PAFPN',
+        deepen_factor = deepen_factor,
+        widen_factor = widen_factor,
+        upsample_feats_cat_first = False,
+        in_channels = [256, 512, 1024],
+        out_channels = [128, 256, 512],
+        norm_cfg=dict(type='BN', momentum=0.03, eps=0.001),
+        act_cfg = dict(type='SiLU', inplace=True),
+    ),
+    bbox_head = dict(
+        head_module = dict(
+            in_channels = [256, 512, 1024])) # 注意使用 YOLOv7PAFPN 后 head 部分输入通道数是 neck 输出通道数的两倍
+)
+```
+
+### 3. YOLOv5 HeadModule 替换
+
+(1) 假设想将 `yolov5 backbone + yolov5 neck + yolo7 headmodule` 作为 `YOLOv5` 的完整网络，则配置文件如下：
+
+```python
+_base_ = './yolov5_s-v61_syncbn_8xb16-300e_coco.py'
+
+strides = [8, 16, 32]
+num_classes = 1 # 根据自己的数据集调整
+
+model = dict(
+    bbox_head=dict(
+        type='YOLOv7Head',
+        head_module=dict(
+            type='YOLOv7HeadModule',
+            num_classes=num_classes,
+            in_channels=[256, 512, 1024],
+            featmap_strides=strides,
+            num_base_priors=3)))
+```