The structure of geometry_msgs/PoseStamped is documented here: http://ros.org/doc/api/geometry_msgs/html/msg/PoseStamped.html
A PoseStamped message in JSON would therefore look as follows:
{
header: {
seq: <int>,
stamp: {
secs: <int>,
nsecs: <int>
},
frame_id: <string>
},
pose: {
position: {
x: <float>,
y: <float>,
z: <float>
},
orientation: {
x: <float>,
y: <float>,
z: <float>,
w: <float>
}
}
}
The entire JSON message that you would send to rosbridge to publish the message would be:
{
receiver: "/topic",
type: "geometry_msgs/PoseStamped",
msg: { ...as above... }
}
Cheers,
Jon