Graphs

Graphs are scene objects that can record and visualize data from a simulation. Data is recorded in data streams, which are sequential lists of values associated with time stamps.

Data streams can directly be visualized as time plots. By combining 2 or 3 data streams, one can obtain x/y curves, or 3D curves in the scene. Following figure illustrates a time plot, showing 6 data streams visualizing joint velocities:

[Examples of a time plot]

A graph is added to the scene with [Add > Graph]. Its basic properties are accessed and adjusted in the graph dialog.

The user is in charge of defining data streams, curves, and feeding them with appropriate data on a regular basis (usually once per simulation step). Following illustrates how to record and visualize 2 data streams (the velocity of two joints over time):

#python

#import math

def sysCall_init():
    sim = require('sim')
    self.joint1Handle = sim.getObject('/joint1')
    self.joint2Handle = sim.getObject('/joint2')
    self.graph = sim.getObject('/Graph')
    self.joint1Vel = sim.addGraphStream(self.graph, 'joint 1 velocity', 'deg/s', 0, [1, 0, 0])
    self.joint2Vel = sim.addGraphStream(self.graph, 'joint 2 velocity', 'deg/s', 0, [0, 1, 0])

def sysCall_sensing():
    sim.setGraphStreamValue(self.graph, self.joint1Vel, 180 * sim.getJointVelocity(self.joint1Handle) / math.pi)
    sim.setGraphStreamValue(self.graph, self.joint2Vel, 180 * sim.getJointVelocity(self.joint2Handle) / math.pi)

--lua

function sysCall_init()
    sim = require('sim')
    joint1Handle = sim.getObject('/joint1')
    joint2Handle = sim.getObject('/joint2')
    graph = sim.getObject('/Graph')
    joint1Vel = sim.addGraphStream(graph, 'joint 1 velocity', 'deg/s', 0, {1, 0, 0})
    joint2Vel = sim.addGraphStream(graph, 'joint 2 velocity', 'deg/s', 0, {0, 1, 0})
end

function sysCall_sensing()
    sim.setGraphStreamValue(graph, joint1Vel, 180 * sim.getJointVelocity(joint1Handle) / math.pi)
    sim.setGraphStreamValue(graph, joint2Vel, 180 * sim.getJointVelocity(joint2Handle) / math.pi)
end

Next example shows how to record and visualize an x/y position curve of an object:

#python

def sysCall_init():
    sim = require('sim')
    self.objectHandle = sim.getObject('/object')
    self.graph = sim.getObject('/Graph')
    self.objectPosX = sim.addGraphStream(self.graph, 'object pos x', 'm', 1)
    self.objectPosY = sim.addGraphStream(self.graph, 'object pos y', 'm', 1)
    sim.addGraphCurve(self.graph, 'object pos x/y', 2, [objectPosX, objectPosY], [0, 0], 'm by m')

def sysCall_sensing():
    pos = sim.getObjectPosition(self.objectHandle)
    sim.setGraphStreamValue(self.graph, self.objectPosX, pos[0])
    sim.setGraphStreamValue(self.graph, self.objectPosY, pos[1])

--lua

function sysCall_init()
    sim = require('sim')
    objectHandle = sim.getObject('/object')
    graph = sim.getObject('/Graph')
    objectPosX = sim.addGraphStream(graph, 'object pos x', 'm', 1)
    objectPosY = sim.addGraphStream(graph, 'object pos y', 'm', 1)
    sim.addGraphCurve(graph, 'object pos x/y', 2, {objectPosX, objectPosY}, {0, 0}, 'm by m')
end

function sysCall_sensing()
    local pos = sim.getObjectPosition(objectHandle)
    sim.setGraphStreamValue(graph, objectPosX, pos[1])
    sim.setGraphStreamValue(graph, objectPosY, pos[2])
end

See also the API functions related to graphs.