[doc] 📝 update dataset

doc/dataset.md

@@ -0,0 +1,102 @@
+<!--
+ * @Date: 2021-06-07 11:57:34
+ * @Author: Qing Shuai
+ * @LastEditors: Qing Shuai
+ * @LastEditTime: 2021-06-07 14:45:17
+ * @FilePath: /EasyMocapRelease/doc/dataset.md
+-->
+# EasyMoCap - Dataset
+
+For convenience, all of the data used by EasyMoCap share the same format.
+
+## Input structure
+
+```bash
+<seq>
+├── intri.yml
+├── extri.yml
+└── videos
+    ├── 1.mp4
+    ├── 2.mp4
+    ├── ...
+    ├── 8.mp4
+    └── 9.mp4
+```
+
+You can use this commond to extract the videos to images:
+```bash
+python3 scripts/preprocess/extract_video.py ${data} --no2d
+```
+
+After this, the folder will be like:
+```bash
+<seq>
+├── intri.yml
+├── extri.yml
+└── images
+    ├── 1
+    │   ├── 000000.jpg
+    │   ├── 000001.jpg
+    │   ├── 000002.jpg
+    │   └── ...
+    ├── 2
+    │   ├── 000000.jpg
+    │   ├── 000001.jpg
+    │   ├── 000002.jpg
+    │   └── ...
+    ├── ...
+    ├── ...
+    ├── 8
+    │   ├── 000000.jpg
+    │   ├── 000001.jpg
+    │   ├── 000002.jpg
+    │   └── ...
+    └── 9
+        ├── 000000.jpg
+        ├── 000001.jpg
+        ├── 000002.jpg
+        └── ...
+```
+
+## 2D Pose
+
+For each image, we record its 2D pose in a `json` file. For an image at `root/images/1/000000.jpg`, the 2D pose willl store at `root/annots/1/000000.json`. The content of the annotation file is:
+
+```bash
+{
+    "filename": "images/0/000000.jpg",
+    "height": <the height of image>,
+    "width": <the width of image>,
+    "annots:[
+        {
+            'personID': 0, # ID of person
+            'bbox': [l, t, r, b, conf],
+            'keypoints': [[x0, y0, c0], [x1, y1, c1], ..., [xn, yn, cn]],
+            'area': <the area of bbox>
+        },
+        {
+            'personID': 1, # ID of person
+            'bbox': [l, t, r, b, conf],
+            'keypoints': [[x0, y0, c0], [x1, y1, c1], ..., [xn, yn, cn]],
+            'area': <the area of bbox>
+        }
+    ]
+}
+```
+
+The definition of the `keypoints` is `body25`. If you want to use other definitions, you should add it to `easymocap/dataset/config.py`
+
+## 3D Pose
+
+```bash
+[
+    {
+        'id': <id>, # the person ID
+        'keypoints3d': [[x0, y0, z0, c0], [x1, y1, z0, c1], ..., [xn, yn, zn, cn]], # x,y,z is the 3D coordinates, c means the confidence of this joint. If the c=0, it means this joint is invisible.
+    },
+    {
+        'id': <id>, # the person ID
+        'keypoints3d': [[x0, y0, z0, c0], [x1, y1, z0, c1], ..., [xn, yn, zn, cn]], # x,y,z is the 3D coordinates, c means the confidence of this joint. If the c=0, it means this joint is invisible.
+    }
+]
+```