Remove grid from composite types.
Replaced it with flexcomp in the models. PiperOrigin-RevId: 730070619 Change-Id: Icbc69e4c6784c6252743f689a1eafb6482d0c393
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Alessio Quaglino
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Copybara-Service
Copybara-Service
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@@ -2982,7 +2982,7 @@ coordinates results in compiler error. See :ref:`CComposite` in the modeling gui
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.. _body-composite-type:
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:at:`type`: :at-val:`[particle, grid, cable, rope, loop, cloth, box, cylinder, ellipsoid], required`
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:at:`type`: :at-val:`[particle, cable], required`
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This attribute determines the type of composite object. The remaining attributes and sub-elements are then
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interpreted according to the type. Default settings are also adjusted depending on the type.
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@@ -2993,13 +2993,6 @@ coordinates results in compiler error. See :ref:`CComposite` in the modeling gui
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and replace the default sphere with a custom geom. Note that the particle composite type is deprecated and might be
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removed in a future version. Instead of particle, it is recommended to use :ref:`replicate`.
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The **grid** type creates a 1D or 2D grid of bodies, each having a sphere geom, a sphere site, and 3 orthogonal
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sliding joints by default. The :el:`pin` sub-element can be used to specify that some bodies should not have joints,
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and instead should be pinned to the parent body. Unlike the particle type, here each two neighboring bodies are
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connected with a spatial tendon whose length is equality-constrained to its initial value (the sites are needed to
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define the tendons). The "main" tendons are parallel to the axes of the grid. In addition one can create diagonal
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"shear" tendons, using the :el:`tendon` sub-element. This type is suitable for simulating strings as well as cloth.
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The **cable** type creates a 1D chain of bodies connected with ball joints, each having a geom with user-defined type
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(cylinder, capsule or box). The geometry can either be defined with an array of 3D vertex coordinates :at:`vertex`
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or with prescribed functions with the option :at:`curve`. Currently, only linear and trigonometric functions are
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@@ -3007,34 +3000,6 @@ coordinates results in compiler error. See :ref:`CComposite` in the modeling gui
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:at:`size`, resulting in :math:`f(s)=\{\text{size}[1]\cdot\cos(2\pi\cdot\text{size}[2]),\;
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\text{size}[1]\cdot\sin(2\pi\cdot\text{size}[2]),\; \text{size}[0]\cdot s\}`.
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The **cloth** type is a different way to model cloth, beyond type="grid". Here the elements are connected with
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universal joints and form a kinematic spanning tree. The root of the tree is the parent body, and its coordinates in
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the grid are inferred from its name - similar to rope but here the naming format is "CB2_0". Neighboring bodies that
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are not connected with joints are then connected with equality-constrained spatial tendons. The resulting cloth is
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non-homogeneous, because the kinematic constraints cannot be violated while the tendon equality constraints are soft.
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One can make it more homogeneous by adding stretch and twist joints (similar to rope) and adjusting the strength of
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their equality constraints. Shear tendons can also be added. In addition to the different physics, cloth can do
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things that a 2D grid cannot do. This is because the elements of cloth have both position and orientation, while the
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elements of grid can only translate. The geoms used in cloth can be ellipsoids and capsules in addition to spheres.
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When elongated geoms are used, they are rotated and interleaved in a pattern that fills the holes, preventing objects
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from penetrating the cloth. Furthermore the inertia of the cloth elements can be modified with the flatinertia
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attribute, and can then be used with lift and drag forces to simulate ripple effects.
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The **box** type creates a 3D arrangement of bodies forming the outer shell of a (soft) box. The parent body is at
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the center of the box. Each element body has a geom (sphere, ellipsoid or capsule) and a single sliding joint
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pointing away from the center of the box. The sliding joints are equality-constrained to their initial value.
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Furthermore, to achieve smooth deformations of the sides of the box, each joint is equality-constrained to remain
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equal to its neighbor joints. To preserve the volume of the soft box approximately, a fixed tendon is used to
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constrain the sum of all joints to remain constant. When the user specifies elongated geoms (capsules or ellipsoids)
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their long axis is aligned with the sliding joint axis. This makes the shell thicker for collision detection
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purposes, preventing objects from penetrating the box. It is important to disable contacts between the elements of
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the box. This is done by setting the default geom contype to 0. The user can change it of course, but if the geoms
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comprising the soft box are allowed to contact each other the model will not work as intended.
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The **cylinder** and **ellipsoid** types are the same as box, except the elements are projected on the surface of an
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ellipsoid or a cylinder respectively. Thus the composite soft body shape is different, while everything else is the
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same as in the box type.
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.. _body-composite-count:
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:at:`count`: :at-val:`int(3), required`
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@@ -48,6 +48,7 @@ General
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Previously, if the volumetric inertia computation failed (for example due to a very flat mesh), the compiler
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would silently fall back to surface inertia computation. Now, the compiler will throw an informative error.
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- Removed the composite type ``grid``. Users should instead use :ref:`flexcomp<body-flexcomp>`.
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MJX
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^^^
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+3
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@@ -1193,47 +1193,10 @@ a more complete treatment, see again the :ref:`deformable <CDeformable>` section
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flex, see the folder `elasticity/ <https://github.com/google-deepmind/mujoco/tree/main/model/plugin/elasticity>`__ for
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several examples.
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**1D grid**.
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**Grid**.
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|image6| |image7|
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.. code-block:: xml
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<composite type="grid" count="20 1 1" spacing="0.045" offset="0 0 1">
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<joint kind="main" damping="0.001"/>
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<tendon kind="main" width="0.01"/>
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<geom size=".02" rgba=".8 .2 .1 1"/>
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<pin coord="1"/>
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<pin coord="13"/>
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</composite>
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The grid type can create 1D or 2D grids, depending on the :at:`count` attribute. Here we illustrate 1D grids. These
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are strings of spheres connected with tendons whose length is soft-equality-constrained. The softness can be adjusted.
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Similar to particles, the element bodies here have slider joints but no rotational joints. The plot on the right
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illustrates pinning. The :el:`pin` sub-element is used to specify the grid coordinates of the pinned bodies, and the
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model compiler does not generate joints for these bodies, thereby fixing them rigidly to the parent body (in this case
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the world). This makes the string in the right plot hang in space. The same mechanism can be used to model a whip for
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example; in that case the parent body would be moving, and the first element body would be pinned to the parent.
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**2D grid**.
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|image8| |image9|
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.. code-block:: xml
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<composite type="grid" count="9 9 1" spacing="0.05" offset="0 0 1">
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<skin material="matcarpet" inflate="0.001" subgrid="3" texcoord="true"/>
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<geom size=".02"/>
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<pin coord="0 0"/>
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<pin coord="8 0"/>
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</composite>
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A 2D grid can be used to simulate cloth. What it really simulates is a 2D grid of spheres connected with
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equality-constrained tendons (not shown). The model compiler can also generate skin, enabled with the :el:`skin`
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sub-element in the above XML. Some of the element bodies can also be pinned, similar to 1D grids but using two grid
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coordinates. The plot on the right shows a cloth pinned to the world body at the two corners, and draping over our
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capsule probe. The skin on the right is subdivided using bi-cubic interpolation, which increases visual quality in the
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absence of textures. When textures are present (left) the benefits of subdivision are less visible.
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The grid composite type has been removed. It is recommended to use 2D flex :ref:`deformable objects <CDeformable>` for
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simulating thin elastic structures.
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**Cable**.
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