update wiki about deformation engine

pyproject.toml

@@ -6,7 +6,7 @@ requires-python = ">=3.10"
 keywords = ["lunar", "simulator", "rover", "locomotion", "IsaacSim"]
 authors = [
     { name = "Antoine Richard", email = "antoine.richard@uni.lu" },
-    { name = "Junnosuke Kamohara", email = "xxx@gatech.edu" },
+    { name = "Junnosuke Kamohara", email = "jkamohara3@gatech.edu" },
 ]
 
 dependencies = [

wiki/deformation_engine/DeformationEngine.md

@@ -1,85 +1,108 @@
 # Deformation Engine
 
-> [!WARNING]
-> This wiki page is under construction
+<center>
+<img src="..//media/deformation_engine_img/deformation.png" width=500>
+</center>
 
 Here, the docs gives a brief explanation of deformation engine plugin. \
 In hydra cfg file (see `cfg/environment/**.yaml`), you have specific lines for terrain deformation. 
 
 ```yaml
 deformation_engine:
     enable: True
-    render_deform_inv: 10
+    delay: 2.0 # how many frames to hold before you apply deformation
     terrain_width: ${....lunaryard_settings.lab_width}
     terrain_height: ${....lunaryard_settings.lab_length}
     terrain_resolution: ${....lunaryard_settings.resolution}
-    gravity: [0, 0, -49.0] #mg
-    force_depth_slope: 0.00014
-    force_depth_intercept: 0.008
-    wheel_params:
-        wheel_width: 0.09
-        wheel_radius: 0.1
-    deform_constraint:
-        deform_offset: 0.0
+    num_links: 4 # num_robots * num_target_links
+    footprint:
+        width: 0.25
+        height: 0.1
+    deform_constrain:
+        x_deform_offset: 0.0
+        y_deform_offset: 0.0
         deform_decay_ratio: 0.01
-    force_distribution: 
+    depth_distribution: 
         distribution: sinusoidal
-        wave_frequency: 2.0
+        wave_frequency: 4.14 # num_grouser/pi (no slip)
     boundary_distribution: 
         distribution: trapezoidal
-        angle_of_repose: 1.047
+        angle_of_repose: 1.047 #pi/3
+    force_depth_regression:
+        amplitude_slope: 0.00006
+        amplitude_intercept: 0.008
+        mean_slope: -0.00046
+        mean_intercept: -0.0013
 ```
 
-## Wheel parameters
-
-You must specify the dimension of your wheels in meter. 
+## Footprint
+This configuration specifies the dimensions of the robot's footprint. \
+For now, we assume the footprint is rectangular since we are primarily focused on wheeled robots. \
+Height and width correspond to the dimensions along the x and y axes (the robot's forward direction is along the x-axis).
 ```yaml
-wheel_params:
-    wheel_width: 0.09
-    wheel_radius: 0.1
+footprint:
+    width: 0.25
+    height: 0.1
 ```
 
-### Deformation Constraint
-Here you will specify parameter for constraint. \
-`deform_offsest` is the distance between wheel origin and the center of deformation profile. \
-`deform_decay_ratio` is decaying parameter of deformation. \
-This is to limit deformation depth as rover traverse the same place many times. 
+### Deform Constraint
+Here, you will specify the parameters for the constraint. \
+`*_deform_offsest` refers to the distance between the projected wheel origin and the center of the deformation profile. \
+`deform_decay_ratio` is the decay parameter for deformation. \
+This is used to limit the deformation depth as the rover traverses the same location multiple times. \
+Given the number of traversals $t$, the actual deformation value will be multiplied by scale factor $\text{ratio}^t$.
 ```yaml
-deform_constraint:
-    deform_offset: 0.0
+deform_constrain:
+    x_deform_offset: 0.0
+    y_deform_offset: 0.0
     deform_decay_ratio: 0.01
 ```
 
-## Force Distribution 
-Controls distribution of force over wheel footprint.
-You have two options for this. 
+## Depth Distribution 
+This controls the xz distribution of the deformation profile.\
+You have three options: uniform, sinusoidal, and trapezoidal.\
+Typically, if your wheel has grousers, the wheel trace will exhibit a sinusoidal pattern.\
+If your wheel has no grousers, the wheel trace is usually uniform.\
+If the sand is cohesive, the trace tends to resemble a trapezoidal shape.
 
 ```yaml
 force_distribution: 
     distribution: uniform
-```
-
-```yaml
+---
 force_distribution: 
     distribution: sinusoidal
     wave_frequency: 2.0
+---
+force_distribution: 
+    distribution: trapezoidal
+    wave_frequency: 2.0
 ```
 
 ## Boundary Distribution
-Controls boundary shape (y axis vs z axis with FLU convention). 
+This controls the yz distribution of the deformation profile.\
+The angle of repose is determined by the type of sand being used.
 
 ```yaml
 boundary_distribution: 
     distribution: uniform
-```
-
-```yaml
+---
 boundary_distribution: 
     distribution: parabolic
-```
-
-```yaml
+---
 boundary_distribution: 
     distribution: trapezoidal
     angle_of_repose: 1.047
+```
+
+## Force depth regression
+To compute deformation depth from the contact force, we use a linear model.\
+Each coefficient is determined by linear regression using DEM simulation data.\
+Note that this model is quite simple, and it will be necessary to develop a higher-dimensional model for more accurate depth computation.
+
+```yaml
+force_depth_regression:
+    amplitude_slope: 0.00006
+    amplitude_intercept: 0.008
+    mean_slope: -0.00046
+    mean_intercept: -0.0013
 ```

wiki/deformation_engine/_Footer.md

@@ -1 +1 @@
-Antoine Richard -- University of Luxembourg -- Space Robotics Group -- 2023-24
+Junnosuke Kamohara -- Georgia Institute of Technology -- 2023-24 -- Work done while he was in Space Robotics Lab in Japan.