Gazebo DataPacks

The JSON implementation always uses JsonDataPack to exchange data with TFs. This datapack can contain arbitrary data in a JSON object. The gRPC implementation uses Protobuf DataPacks. Below are listed the protobuf message definitions used by the Gazebo engine:

syntax = "proto3";
 
package Gazebo;
 
/*
 * Data coming from gazebo camera datapack
 */
message Camera
{
    uint32 imageWidth  = 1;
    uint32 imageHeight = 2;
    uint32 imageDepth  = 3;
    bytes  imageData   = 4;
}
 
/*
 * Data coming from gazebo link datapack
 */
message Link
{
    repeated float position        = 1;
    repeated float rotation        = 2;
    repeated float linearVelocity  = 3;
    repeated float angularVelocity = 4;
}
 
/*
 * Data coming from gazebo model datapack
 */
message Model
{
    repeated float position        = 1;
    repeated float rotation        = 2;
    repeated float linearVelocity  = 3;
    repeated float angularVelocity = 4;
}
 
/*
 * Data coming from gazebo joint datapack
 */
message Joint
{
    float position = 1;
    float velocity = 2;
    float effort   = 3;
}
 
// EOF

For each of these definitions, a datapack Python class is generated, see here for more details. Concretely, these datapack types are generated:

• GazeboCameraDataPack: contains a camera image
• GazeboJointDataPack: contains a single joint state information
• GazeboLinkDataPack: contains a single link state information
• GazeboModelDataPack: contains a single model state information

In the case of the JSON implementation, even if JsonDataPack, the content of the datapacks data will be the same, but stored as a JSON object. This content is summarized below for each datapack type.

The GazeboCameraDataPack consists of the following attributes:

GazeboCameraDataPack Attributes

Attribute	Description	Python Type	C type
image_height	Camera Image height	uint32	uint32
image_width	Camera Image width	uint32	uint32
image_depth	Camera Image depth. Number of bytes per pixel	uint8	uint32
image_data	Camera Image data. 1-D array of pixel data	numpy.array(image_height * image_width * image_depth, numpy.uint8)	std::vector<unsigned char>

The GazeboJointDataPack consists of the following attributes:

GazeboJointDataPack Attributes

Attribute	Description	Python Type	C type
position	Joint angle position (in rad)	float	float
velocity	Joint angle velocity (in rad/s)	float	float
effort	Joint angle effort (in N)	float	float

The GazeboLinkDataPack consists of the following attributes:

GazeboLinkDataPack Attributes

Attribute	Description	Python Type	C type
pos	Link Position	numpy.array(3, numpy.float32)	std::array<float,3>
rot	Link Rotation as quaternion	numpy.array(4, numpy.float32)	std::array<float,4>
lin_vel	Link Linear Velocity	numpy.array(3, numpy.float32)	std::array<float,3>
ang_vel	Link Angular Velocity	numpy.array(3, numpy.float32)	std::array<float,3>

Each of this attributes can be accessed under their respective names from the data attribute of each DataPack type.