World¶

raisim::World class creates/manages all resources. All objects defined in the same World class instance can collide with each other unless otherwise their collision mask and group explicitly disables the collision (read Contact and Collision section for this topic).

There are two ways to generate the World instance (i.e., two constructors). The first way is to load an raisim world configuration file, which is in a form of an XML file. You can read more about the XML format in the World Configuration File section.

The second way is to generate world dynamically in code.

You can also mix the two ways, by loading an XML file and dynamically adding objects.

There is an experimental MJCF (MuJoCo file format) reader. Simple models can be constructed with an MJCF file.

Adding New Objects¶

To add a new object of a shape X, a method named addX is used. For example, to add a sphere

raisim::World world;
auto sphere = world.addSphere(0.5, 1.0);

Here sphere is a pointer to the internal resource. It can be used to access or to modify the internal variables.

There are three hidden arguments to all object-creation methods: material, collisionGroup and collisionMask. Descriptions of the collision variables are given in “Collision and Contact” chapter. material argument specifies the material which governs contact dynamics. It is further explained in “Material System” chapter.

The list of objects is given in “Object” chapter.

Once an object is added, a name can be set as below

sphere.setName("ball");

A pointer to an object with a specific name can be retrieved as below

auto ball = world.getObject("ball");

An object might contain multiple bodies (i.e., articulated system). To designate each body, local index can be used. To keep the interface consistent, many methods ask for the local index even for simgle body objects. In a single body object case, local index arguments are ignored and users can simply put 0 to comply with the AIP.

Save world to an XML file¶

raisim::World::exportToXml() lets you save the world to an XML file. EXAMPLES

MuJoCo mjcf file loader¶

RaiSim partially supports mjcf file. There are inherent differences between the two simulators and inevitably some features are not supported. But you can load simple mjcf files (e.g., ones provided by OpenAI).

Changing Simulation Parameters¶

The following parameters can be changed using the world API

Time step

RaiSim uses a fixed time step. The time step obtained and modified using getTimeStep and setTimeStep method.

API¶

class raisim::World¶

Public Functions

explicit World()¶: Create an empty world

explicit World(const std::string &configFile)¶: Create an world as specified in the xml config file

void exportToXml(const std::string &dir, const std::string &fileName)¶

export the world to an xml config file, which can be loaded using a constructor

Parameters

dir – directory to save the xml file
fileName – file name

inline void setTimeStep(double dt)¶

set the time step

Parameters: dt – the time step

inline double getTimeStep() const¶

Returns: the time step

Sphere *addSphere(double radius, double mass, const std::string &material = "default", CollisionGroup collisionGroup = 1, CollisionGroup collisionMask = CollisionGroup(-1))¶

Parameters

radius – radius
mass – mass
material – material of the height map (which defines the contact dynamics)
collisionGroup – read “Contact and Collision/ Collision Group and Mask”
collisionMask – read “Contact and Collision/ Collision Group and Mask”.

Returns

pointer to the created box

Box *addBox(double xLength, double yLength, double zLength, double mass, const std::string &material = "default", CollisionGroup collisionGroup = 1, CollisionGroup collisionMask = CollisionGroup(-1))¶

Parameters

xLength – x dimension
yLength – y dimension
zLength – z dimension
mass – mass
material – material of the height map (which defines the contact dynamics)
collisionGroup – read “Contact and Collision/ Collision Group and Mask”
collisionMask – read “Contact and Collision/ Collision Group and Mask”.

Returns

pointer to the created box

Cylinder *addCylinder(double radius, double height, double mass, const std::string &material = "default", CollisionGroup collisionGroup = 1, CollisionGroup collisionMask = CollisionGroup(-1))¶

Parameters

radius – radius
height – center-to-center distance
mass – mass
material – material of the height map (which defines the contact dynamics)
collisionGroup – read “Contact and Collision/ Collision Group and Mask”
collisionMask – read “Contact and Collision/ Collision Group and Mask”.

Returns

pointer to the created cylinder

Capsule *addCapsule(double radius, double height, double mass, const std::string &material = "default", CollisionGroup collisionGroup = 1, CollisionGroup collisionMask = CollisionGroup(-1))¶

Parameters

radius – radius
height – center-to-center distance
mass – mass
material – material of the height map (which defines the contact dynamics)
collisionGroup – read “Contact and Collision/ Collision Group and Mask”
collisionMask – read “Contact and Collision/ Collision Group and Mask”.

Returns

pointer to the created capsule

Ground *addGround(double zHeight = 0.0, const std::string &material = "default", CollisionGroup collisionMask = CollisionGroup(-1))¶

Parameters

zHeight – height of the terrain
material – material of the height map (which defines the contact dynamics)
collisionMask – read “Contact and Collision/ Collision Group and Mask”. Note that collision group of a static object is CollisionGroup(1) << 61ul

Returns

pointer to the created ground

HeightMap *addHeightMap(size_t xSamples, size_t ySamples, double xSize, double ySize, double centerX, double centerY, const std::vector<double> &height, const std::string &material = "default", CollisionGroup collisionGroup = RAISIM_STATIC_COLLISION_GROUP, CollisionGroup collisionMask = CollisionGroup(-1))¶

Parameters

xSamples – how many points along x axis
ySamples – how many points along y axis
xSize – x width of the height map
ySize – y length of the height map
centerX – x coordinate of the center of the height map
centerY – y coordinate of the center of the height map
height – a vector of doubles representing heights. the size should be xSample X ySamples
material – material of the height map (which defines the contact dynamics)
collisionGroup – read “Contact and Collision/ Collision Group and Mask”
collisionMask – read “Contact and Collision/ Collision Group and Mask”

Returns