sim-scripting-intro.md

Sim Scripting Intro

In the sim, objects are interacted with via handles, which are ints that correspond to a particular object

To get an object handle from a name, do sim.getObjectHandle('ObjectName')

Useful Sim Methods

• sim.getObjectPosition(handle, relToHandle), where relToHandle is the handle of the frame you want the position in. -1 for the global frame
• sim.getObjectMatrix(handle, relToHandle) for object's rotation matrix
• sim.getObjectQuaternion(handle, relToHandle) for object's orientation as quaternion
• TODO: whatever I did to walk the object tree and make them semi-transparent

Outputting transforms to ROS

The sim can put transforms directly into the ROS /tf topic!

1. Copypaste this function into the script of the component you want the transform for:

   -- copypasted from https://forum.coppeliarobotics.com/viewtopic.php?t=6198
   function getTransformStamped(objHandle,name,relTo,relToName)
       t=sim.getSystemTime()
       p=sim.getObjectPosition(objHandle,relTo)
       o=sim.getObjectQuaternion(objHandle,relTo)
   
       return {
           header={
               stamp=t,
               frame_id=relToName
           },
           child_frame_id=name,
           transform={
               -- ROS has definition x=front y=side z=up
               translation={x=p[1],y=p[2],z=p[3]},--V-rep
               rotation={x=o[1],y=o[2],z=o[3],w=o[4]}--v-rep
           }
       }
   end
   

   name is the name of the child frame, and relToName is the name of the parent frame. This function returns a table that is equivalent to the ROS /tf message with the same fields.
2. Send the transform

   tf = getTransformStamped(J1, 'J1_PSM1', -1, 'simworld')
   simROS.sendTransform(tf)