title: Observation dictionary

The observation at each step is a dictionary with following keys:

| ---:| --- |
| body_pos | Positions of body parts along (X,Y,Z) |
| body_pos_rot | Rotations of body parts along (X,Y,Z) |
| body_vel | Velocities of body parts along (X,Y,Z) |
| body_vel_rot | Rotational velocities of body parts along (X,Y,Z) |
| body_acc | Accelerations of body parts along (X,Y,Z) |
| body_acc_rot | Rotational accelerations of body parts along (X,Y,Z) |
| joint_pos | Positions of joints |
| joint_vel | Velocities of joints |
| joint_acc | Accelerations of joints |
| muscles | Forces acting on body parts |
| forces | Forces acting on body parts |
| misc | Forces acting on body parts |
| markers | Empty for this model |

Each element is a dictionary.

Body parts

The model has following bodies

| ---:| --- |
| calcn_l | Left calcaneus |
| talus_l | Left talus |
| tibia_l | Left tibia |
| toes_l | Left toes |
| femur_l | Left femur |
| femur_r | Right femur |
| head | Head |
| pelvis | Pelvis |
| torso | Torso |
| pros_foot_r | Prosthetic foot |
| pros_tibia_r | Prosthetic tibia |

Each element is a vector. Elements corresponding to each transational position, velocity, and acceleration is order as [x,y,z]. Rotational position, velocity, and acceleration vectors correspond to rotations along X, Y, and Z.

Joints

The model has following joints

| name | length | description |
| ankle_l | 1 | Left ankle flexion |
| ankle_r | 1 | Right ankle flexion |
| back | 1 | Back flexion |
| ground_pelvis | 6 | translation (x,y,z) and rotation along x, y, and z |
| hip_l | 3 | Hip flexion, abduction, and rotation |
| hip_r | 3 | Hip flexion, abduction, and rotation |
| knee_l | 1 | Left knee flexion |
| knee_r | 1 | Right knee flexion |

Extra joints back_0, mtp_l, subtalar_l appear in the dictionary for consistency but they cannot move.

Muscles

| name | description | primary function(s) |
| abd_l | Hip abductors (left) | Hip abduction (away from body's vertical midline) |
| abd_r | Hip abductors (right) | Hip abduction (away from body's vertical midline) |
| add_l | Hip adductors (left) | Hip adduction (toward body's vertical midline) |
| add_r | Hip adductors (right) | Hip adduction (toward body's vertical midline) |
| bifemsh_l | Short head of the biceps femoris (left) | Knee flexion |
| bifemsh_r | Short head of the biceps femoris (right) | Knee flexion |
| gastroc_l | Gastrocnemius (left) | Knee flexion and ankle extension (plantarflexion) |
| glut_max_l | Gluteus maximus (left) | Hip extension |
| glut_max_r | Gluteus maximums (left) | Hip extension |
| hamstrings_l | Biarticular hamstrings (left) | Hip extension and knee flexion |
| hamstrings_r | Biarticular hamstrings (right) | Hip extension and knee flexion |
| iliopsoas_l | iliopsoas (left) | Hip flexion |
| iliopsoas_r | iliopsoas (right) | Hip flexion |
| rect_fem_l | rectus femoris (left) | Hip flexion and knee extension |
| rect_fem_r | rectus femoris (right) | Hip flexion and knee extension |
| soleus_l | soleus (left) | Ankle extension (plantarflexion) |
| tib_ant_l | tibialis anterior (left) | Ankle flexion (dorsiflexion) |
| vasti_l | vasti (left) | Knee extension
| vasti_r | vasti (right) | Knee extension

Each muscle element is a dictionary with 4 elements

| ---:| --- |
| activation | Current activation |
| fiber_force | Current fiber force |
| fiber_length | Current fiber length |
| fiber_velocity | Current fiber velocity |

Forces

| ---:| --- |
| AnkleLimit_l | Ankle ligament forces (left) |
| AnkleLimit_r | Ankle ligament forces (right) |
| HipAddLimit_l | Hip adduction/abduction ligament forces (left) |
| HipAddLimit_r | Hip adduction/abduction ligament forces (right) |
| HipLimit_l | Hip flexion/extension ligament forces (left) |
| HipLimit_r | Hip flexion/extension ligament forces (right) |
| KneeLimit_l | Knee flexion/extension ligament forces (left) |
| KneeLimit_r | Knee flexion/extension ligament forces (right) |
| foot_l | Ground reaction forces on the left foot. 6 values correspond to the 3 components (x,y,z) of the force and torque applied to the foot_l body. |
| pros_foot_r_0 | Ground reaction forces on the prosthetic foot 6 values correspond to the 3 components (x,y,z) of the force and torque applied to the pros_foot_r body. |

For the difference between muscle forces in this item and fiber_force in muscles please refer to Issue #163

Misc

| ---:| --- |
| mass_center_pos | Position of the center of mass [x,y,z] |
| mass_center_vel | Translational velocity of the center of mass [x,y,z] |
| mass_center_acc | Translational acceleration of the center of mass [x,y,z] |