Collision detection

CoppeliaSim can detect collisions between two collidable entities in a flexible way. The calculation is an exact interference calculation. Collision detection, as its name states, only detect collisions; it does however not directly react to them (for collision response, refer to the dynamics module).

[Collision detection between two manipulators]

Using the API function sim.checkCollision, one can easily detect collision between entities, for instance collision detection between a robot and its environment, from within a simulation script, in each simulation step:

#python

def sysCall_init():
    sim = require('sim')
    robotBase = sim.getObject('/robotModelAlias')
    self.robotCollection = sim.createCollection(0)
    sim.addItemToCollection(robotCollection, sim.handle_tree, robotBase, 0)

def sysCall_sensing():
    result, pairHandles = sim.checkCollision(self.robotCollection, sim.handle_all)
    if result > 0:
        print(f'Robot is colliding. Colliding pair is {getAsString(pairHandles)}')

--lua

function sysCall_init()
    sim = require('sim')
    local robotBase = sim.getObject('/robotModelAlias')
    robotCollection = sim.createCollection(0)
    sim.addItemToCollection(robotCollection, sim.handle_tree, robotBase, 0)
end

function sysCall_sensing()
    local result, pairHandles = sim.checkCollision(robotCollection, sim.handle_all)
    if result > 0 then
        print('Robot is colliding. Colliding pair is ' .. getAsString(pairHandles))
    end
end

One can also temporarily modify the color of objects or whole collections, in order to visually indicate a collision:

#python

def change_pair_color(entity_pair, color_pair):
    self.original_color_data = []
    self.original_color_data.append(sim.changeEntityColor(entity_pair[0], color_pair[0]))
    self.original_color_data.append(sim.changeEntityColor(entity_pair[1], color_pair[1]))

def restore_pair_color():
    if hasattr(self,'original_color_data'):
        sim.restoreEntityColor(self.original_color_data[0])
        sim.restoreEntityColor(self.original_color_data[1])

def sysCall_init():
    sim = require('sim')
    robot_base = sim.getObject('/irb360')
    self.robot_collection = sim.createCollection(0)
    sim.addItemToCollection(self.robot_collection, sim.handle_tree, robot_base, 0)
    self.collision_colors = [[1, 0, 0], [1, 0, 1]]  # collider and collidee

def sysCall_sensing():
    result, pair_handles = sim.checkCollision(self.robot_collection, sim.handle_all)
    restore_pair_color()
    if result > 0:
        # Change color of the collection and the collidee:
        change_pair_color([self.robot_collection, pair_handles[1]], self.collision_colors)
        # Change color of the collider and collidee objects:
        # change_pair_color([pair_handles[0], pair_handles[1]], self.collision_colors)

def sysCall_cleanup():
    restore_pair_color()

--lua

function changePairColor(entityPair, colorPair)
    originalColorData = {}
    originalColorData[1] = sim.changeEntityColor(entityPair[1], colorPair[1])
    originalColorData[2] = sim.changeEntityColor(entityPair[2], colorPair[2])
end

function restorePairColor()
    if originalColorData then
        sim.restoreEntityColor(originalColorData[1])
        sim.restoreEntityColor(originalColorData[2])
        originalColorData = nil
    end
end

function sysCall_init()
    sim = require('sim')
    local robotBase = sim.getObject('/irb360')
    robotCollection = sim.createCollection(0)
    sim.addItemToCollection(robotCollection, sim.handle_tree, robotBase, 0)
    collisionColors = {{1, 0, 0}, {1, 0, 1}}  -- collider and collidee
end

function sysCall_sensing()
    local result, pairHandles = sim.checkCollision(robotCollection, sim.handle_all)
    restorePairColor()
    if result > 0 then
        -- Change color of the collection and the collidee:
        changePairColor({robotCollection, pairHandles[2]}, collisionColors)
        -- Change color of the collider and collidee objects:
        -- changePairColor({pairHandles[1], pairHandles[2]}, collisionColors)
    end
end

function sysCall_cleanup()
    restorePairColor()
end

CoppeliaSim's collision detection functionality is also available as stand-alone routines via the Coppelia geometric routines.

See also the add-on in [Modules > Geometry / Mesh > Collision check ] that allows to quickly check for self-collision, collision with the environment, or collision between two entities.