🌡️ Object States

Description

In OmniGibson, ObjectStates define kinematic (such as OnTop, or Inside) or semantic (such as Temperature or Saturated) states for a given StatefulObject. These states enable finer-grained description of the scene at hand not captured by the raw simulation state (such as object and joint poses).

Every StatefulObject owns its own dictionary of states obj.states, which maps the object state class type to the object state instance owned by the object.

Object states have a unified API interface: a getter state.get_value(...), and a setter state.set_value(...). Note that not all object states implement these functions:

• Some states such as Temperature implement both get_value() and set_value() as a simple R/W operation, as this is merely an internal variable that is tracked over time.
• Other states implement more complex behavior such as OnTop, which infers spatial relationships between different objects during get_value() and additional samples poses in set_value() such that the spatial relationship is true.
• Some states such as NextTo only implement get_value(), since setting these states are non-trivial and unclear to sample.
• Finally, IntrinsicObjectStates such as ParticleApplier (which describes an object that can generate particles, such as a spray bottle) describe an intrinsic semantic property of the object, and therefore do not implement get_value nor set_value.

OmniGibson supports a wide range of object state types, and provides an extensive example suite showcasing individual object states. For more information, check out our object state examples.

Object States must be enabled before usage!

To enable usage of object states, gm.ENABLE_OBJECT_STATES (1) must be set!

1. Access global macros via from omnigibson.macros import gm

Usage

Adding Object States

Object states are intended to be added when an object is instantiated, during its constructor call via the abilities kwarg. This is expected to be a dictionary mapping ability name to a dictionary of keyword-arguments that dictate the instantiated object state's behavior. Normally, this is simply the keyword-arguments to pass to the specific ObjectState constructor, but this can be different. Concretely, the raw values in the abilities value dictionary are postprocessed via the specific object state's postprocess_ability_params classmethod. This is to allow abilities to be fully exportable in .json format, without requiring complex datatypes (which may be required as part of an object state's actual constructor) to be stored.

By default, abilities=None results in an object's abilities directly being inferred from its category kwarg. OmniGibson leverages a crowdsourced knowledgebase to determine what abilities (or "properties" in the knowledgebase) a given entity (called "synset" in the knowledgebase) can have. Every category in OmniGibson's asset dataset directly corresponds to a specific synset. By going to the knowledgebase and clicking on the corresponding synset, one can see the annotated abilities (properties) for that given synset, which will be applied to the object being created.

Alternatively, you can programmatically observe which abilities, with the exact default kwargs, correspond to a given category via:

from omnigibson.utils.bddl_utils import OBJECT_TAXONOMY
category = "apple"      # or any other category
synset = OBJECT_TAXONOMY.get_synset_from_category(category)
abilities = OBJECT_TAXONOMY.get_abilities(synset)

Not all object states are guaranteed to be created!

Some object states (such as ParticleApplier or ToggledOn) potentially require specific metadata to be defined for a given object model before the object state can be created. For example, ToggledOn represents a pressable virtual button, and requires this button to be defined a-priori in the raw object asset before it is imported. When parsing the abilities dictionary, each object state runs a compatibilty check via state.is_compatible(obj, **kwargs) before it is created, where **kwargs define any relevant keyword arguments that would be passed to the object state constructor. If the check fails, then the object state is not created!

Runtime

As mentioned earlier, object states can be potentially read from via get_state(...) or written to via set_state(...). The possibility of reading / writing, as well as the arguments expected and return value expected depends on the specific object state class type. For example, object states that inherit the BooleanStateMixin class expect get_state(...) to return and set_state(...) to receive a boolean. AbsoluteObjectStates are agnostic to any other object in the scene, and so get_state() takes no arguments. In contrast, RelativeObjectStates are computed with respect to another object, and so require other_obj to be passed into the getter and setter, e.g., get_state(other_obj) and set_state(other_obj, ...). A ValueError will be raised if a get_state(...) or set_state(...) is called on an object that does not support that functionality. If set_state() is called and is successful, it will return True, otherwise, it will return False. For more information on specific object state types' behaviors, please see Object State Types.

It is important to note that object states are usually queried / computed on demand and immediately cached until its value becomes stale (usually the immediately proceeding simulation step). This is done for efficiency reasons, and also means that object states are usually not automatically updated per-step unless absolutely necessary (1). Calling state.clear_cache() forces a clearing of an object state's internal cache.

Object State Types

OmniGibson currently supports 34 object states, consisting of 19 AbsoluteObjectStates, 11 RelativeObjectStates, and 4 InstrinsicObjectStates. Below, we provide a brief overview of each type:

AbsoluteObjectState

These are object states that are agnostic to other objects in a given scene.

AABB The axis-aligned bounding box (AABB) of the object in the world frame. get_value(): returns aabb_min, aabb_max set_value(): Not supported.
VerticalAdjacency / HorizontalAdjacency The nearby objects that are considered adjacent to the object, either in the +/- global Z axis or +/- global XY plane. get_value(): returns AxisAdjacencyList, a namedtuple with positive_neighbors and negative_neighbors each of which are lists of nearby objects set_value(): Not supported.
Burnt Whether the object is considered burnt or not. Note that if True, this object's visual appearance will also change accordingly. This corresponds to an object hitting some MaxTemperature threshold over the course of its lifetime. get_value(): returns True / False set_value(new_value): expects True / False
ContactBodies The nearby rigid bodies that this object is currently in contact with. get_value(ignore_objs=None): returns rigid_prims, a set of RigidPrims the object is in contact with, optionally with ignore_objs filtered from the set set_value(new_value): Not supported.
Cooked Whether the object is considered cooked or not. Note that if True, this object's visual appearance will also change accordingly. This corresponds to an object hitting some MaxTemperature threshold over the course of its lifetime. get_value(): returns True / False set_value(new_value): expects True / False
Folded / Unfolded A cloth-specific state. Determines whether a cloth object is sufficiently un / folded or not. This is inferred as a function of its overall smoothness, total area to current area ratio, and total diagonal to current diagonal ratio. get_value(): returns True / False set_value(new_value): Can only set unfolded.set_value(True). All others are not supported.
Frozen Whether the object is considered frozen or not. Note that if True, this object's visual appearance will also change accordingly. This corresponds to an object's Temperature value being under some threshold at the current timestep. get_value(): returns True / False set_value(new_value): expects True / False
HeatSourceOrSink Defines a heat source or sink which raises / lowers the temperature of nearby objects, if enabled. Use state.affects_obj(obj) to check whether the given heat source / sink is currently impacting obj's temperature. get_value(): returns True / False (whether the source / sink is enabled or not) set_value(new_value): Not supported.
Heated Whether the object is considered heated or not. Note that if True, this object's visual appearance will also change accordingly with steam actively coming off of the object. This corresponds to an object's Temperature value being above some threshold at the current timestep. get_value(): returns True / False set_value(new_value): expects True / False
MaxTemperature The object's max temperature over the course of its lifetime. This value gets automatically updated every simulation step and can be affected by nearby HeatSourceOrSink-enabled objects. get_value(): returns float set_value(new_value): expects float
OnFire Whether the object is lit on fire or not. Note that if True, this object's visual appearance will also change accordingly with fire actively coming off of the object. This corresponds to an object's Temperature value being above some threshold at the current timestep. Note that if True, this object becomes an active HeatSourceOrSink-enabled object that will raise the temperature of nearby objects. get_value(): returns True / False set_value(new_value): expects True / False
ObjectsInFOVOfRobot A robot-specific state. Comptues the list of objects that are currently in the robot's field of view. get_value(): returns obj_list, the list of BaseObjects set_value(new_value): Not supported
Open Whether the object's joint is considered open or not. This corresponds to at least one joint being above some threshold from its pre-defined annotated closed state. get_value(): returns True / False set_value(new_value): expects True / False, randomly sampling a valid open / not open configuration unless fully is set
Pose The object's current (position, orientation) expressed in (cartesian, quaternion) form in the global frame. get_value(): returns (pos, quat), with quat in (x,y,z,w) form set_value(new_value): Not supported. Use obj.set_position_orientation() to directly modify an object's pose.
Temperature The object's current temperature. This value gets automatically updated every simulation step and can be affected by nearby HeatSourceOrSink-enabled objects. get_value(): returns float set_value(new_value): expects float
ToggledOn A virtual button that can be "pressed" by a robot's end-effector. Doing so will result in the state being toggled between True and False, and also corresponds to a visual change in the virtual button's appearance. get_value(): returns True / False set_value(new_value): expects True / False

RelativeObjectState

These are object states that are computed with respect to other entities in the given scene, and therefore, both the get_state(...) and set_state(...) take in additional arguments.

AttachedTo Defines a rigid or flexible connection between this object and another object (parent). At any given moment, this object can only be attached to at most one parent, but the reverse is not true. That is, a parent can have multiple children, but a child can only have one parent. An attachment is triggered and created when the this object makes contact with a compatible parent and is aligned correctly. get_value(other): returns True / False, whether this object is attached to other set_value(other, new_value, bypass_alignment_checking=False): expects True / False, and optionally bypasses checking for object alignment with other if bypass_alignment_checking is set
Contains Defines whether this object currently contains any quantity of a specific particle system. Note that this state requires that a container virtual volume be pre-annotated in the underlying object asset for it to be created. Particles are considered contained if their position lies within the annotated volume. get_value(system): returns True / False set_value(system, new_value): Only supported for new_value=False, which will remove all contained particles
Covered Defines whether this object is currently covered by a specific particle system. This corresponds to checking whether the number of particles either touching or attached to this object surpasses some minimum threshold. get_value(system): returns True / False set_value(system, new_value): If True, will sample particles from system on this object, otherwise, will remove all particles from system covering this object
Draped A cloth-specific state. Defines whether this cloth object is fully covering other, e.g., a tablecloth draped over a table. This object is considered draped if it is touching other and its center of mass is below the average position of the contact points. get_value(other): returns True / False set_value(other, new_value): Only supports True, which will try to sample this cloth object on top of other such that draped.get_value(other)=True
Filled Defines whether this object is currently filled with a specific particle system. Note that this state requires that a container virtual volume be pre-annotated in the underlying object asset for it to be created. This state corresponds to checking whether the total volume of contained particles surpasses some minimum relative ratio with respect to its total annotated container volume. get_value(system): returns True / False set_value(system, new_value): If True, will sample particles from system to fill the container volume, otherwise, will remove all particles from system contained within this object
Inside Defines whether this object is considered inside of other. This does raycasting in all axes (x,y,z), and checks to make sure that rays shot in at least two of these axes hit other. get_value(other): returns True / False set_value(other, new_value): Only supported for True, which will sample poses for this object such that get_value(other)=True
IsGrasping A robot-specific state. Determines whether this robot is currently grasping other. get_value(other): returns True / False set_value(other, new_value): Not supported.
NextTo Defines whether this object is considered next to other. This checks to make sure this object is relatively close to other and that other is in either of this object's HorizontalAdjacency neighbor lists. get_value(other): returns True / False set_value(other, new_value): Not supported.
OnTop Defines whether this object is considered on top of other. This checks to make sure that this object is touching other and that other is in this object's VerticalAdjacency negative_neighbors list. get_value(other): returns True / False set_value(other, new_value): Only supported for True, which will sample poses for this object such that get_value(other)=True
Overlaid A cloth-specific state. Defines whether this object is overlaid over other, e.g., a t-shirt overlaid over a table. This checks to make sure that the ratio of this cloth object's XY-projection of its convex hull to other's XY-area of its bounding box surpasses some threshold. get_value(other): returns True / False set_value(other, new_value): Only supports True, which will try to sample this cloth object on top of other such that overlaid.get_value(other)=True
Saturated Defines whether this object has reached the maximum with respect to a specific particle system, e.g., a sponge fully absorbed with water, or a spray bottle fully emptied of cleaner fluid. This keeps a reference to this object's modified particle count for system, and checks whether the current value surpasses a desired limit. Specific limits can be queried via get_limit(system) and set via set_limit(system, limit). Note that if True, this object's visual appearance will also change accordingly. get_value(system): returns True / False set_value(system, new_value): If True, will set the internal modified particle count to exactly to the limit, otherwise, will set to 0.
Touching Defines whether this object is in contact with other. get_value(system): returns True / False set_value(system, new_value): Not supported.
Under Defines whether this object is considered under other. This checks to make sure that this object is touching other and that other is in this object's VerticalAdjacency positive_neighbors list. get_value(other): returns True / False set_value(other, new_value): Only supported for True, which will sample poses for this object such that get_value(other)=True

IntrinsicObjectState

These are object states that that define intrinsic properties of the object and therefore do not implement get_state(...) nor set_state(...).

ParticleApplier / ParticleRemover Defines an object that has the ability to apply (spawn) or remove (absorb) particles from specific particle systems. This state's conditions property defines the per-particle system requirements in order for the applier / remover to be active for that specific system. For example, a spray bottle that is a ParticleApplier may require toggled_on.get_value() to be True in order to allow cleaning_fluid particles to be sprayed, simulating a "press" of the nozzle trigger. The method flag in the constructor determines the applier / removal behavior, which is triggered only by direct contact with the object (ParticleModifyMethod.ADJACENCY) or contact with a virtual volume (ParticleModifyMethod.PROJECTION). The former captures objects such as sponges, while the latter captures objects such as vacuum cleaners or spray bottles. This object state is updated at each simulation step such that particles are automatically added / removed as needed. get_value(): Not supported. set_value(): Not supported.

ParticleSource / ParticleSink Defines an object that has the ability to apply (spawn) or remove (absorb) particles from specific particle systems. The behavior is nearly identical to ParticleApplier / ParticleRemover, with the exception that contact is not strictly necessary to add / remove particles. This is to provide the distinction between, e.g., a particle source such as a sink, which always spawns water every timestep irregardless of whether its faucet volume is in contact with a surface, vs. a particle applier such as a spray bottle, which (for efficiency reasons) only spawns water if its virtual spray cone is overlapping with a surface. get_value(): Not supported. set_value(): Not supported.