📚 Add datalab doc

doc/source/tools/datalab.md

@@ -1,5 +1,20 @@
 # DataLab
 
-## Poselib
+## Parameterized human model from Xsens
 
-### From fbx to npy
+For this part, we can extract parameterized URDF human model from Xsens based on a template URDF model.
+
+1. The template URDF model can be found in [template urdf model](https://github.com/Skylark0924/Rofunc/blob/main/rofunc/simulator/assets/urdf/human/human_xsenstemplate_48dof.urdf). In this urdf, we decouple the ball joints of human into 3 rotation joints in the order of Z-X-Y. 
+2. By following [this example](https://github.com/Skylark0924/Rofunc/blob/main/examples/simulator/example_xsens_to_human_model.py), we can extract the parameters that the template model needs from Xsens mvnx file and generate a new URDF model.
+3. I also have tried to use the joint value in Xsens mvnx file to control this urdf. The trail can be found in [this script](https://github.com/Skylark0924/Rofunc/blob/main/rofunc/simulator/human_sim.py). However, the result is not good, the motion is quite weird. I analyzed that the reason should be the joint values in Xsens mvnx file rotate based on a different axis with our urdf. In order to leverage the experience in AMP and ASE, I finally chose to use the motion retargeting method provided by them.
+
+## Motion retargeting from Xsens
+
+The motion retargeting is not based on URDF model now, it is built on [poselib](https://github.com/Skylark0924/Rofunc/tree/main/rofunc/utils/datalab/poselib) and [MJCF humanoid model](https://github.com/Skylark0924/Rofunc/blob/main/rofunc/simulator/assets/mjcf/amp_humanoid.xml).
+
+1. The poselib can convert the Xsens `.fbx` file to a `.npy` file, please check [this](https://github.com/Skylark0924/Rofunc/blob/main/rofunc/utils/datalab/poselib/fbx_to_amp_npy.py).
+2. The `.npy` motion can be visualized in Isaac Gym by following command
+   ```bash
+   python examples/learning_rl/example_HumanoidASE_RofuncRL.py --task HumanoidViewMotion --motion_file /path/to/motion.npy --headless=False --inference
+   ```
+   Some example data is provided in [`examples/data/ase`](https://github.com/Skylark0924/Rofunc/tree/main/examples/data/ase) and [`examples/data/amp`](https://github.com/Skylark0924/Rofunc/tree/main/examples/data/amp).