Scatter_2d is not guaranting collision free scatter

I am using scatter_2d however my objects of interests (here pallets) that are thrown are not collision free and here they collide with the boxes in This happens despite using check_for_collisions=True so I am not sure what I should use so objects don’t be spawn like this

Randomize boxes materials and their location on the surface of the given prim

def register_scatter_pallets(prim):
    # Calculate the bounds of the prim to create a scatter plane of its size
    bb_cache = create_bbox_cache()
    bbox3d_gf = bb_cache.ComputeLocalBound(prim)
    prim_tf_gf = omni.usd.get_world_transform_matrix(prim)

    # Calculate the bounds of the prim
    range_size = bbox3d_gf.GetRange().GetSize()

    # Get the quaterion of the prim in xyzw format from usd
    prim_quat_gf = prim_tf_gf.ExtractRotation().GetQuaternion()
    prim_quat_xyzw = (prim_quat_gf.GetReal(), *prim_quat_gf.GetImaginary())

    # Create a plane on the pallet to scatter the boxes on
    plane_scale = (range_size[0] * 5, range_size[1] * 5, 1)
    plane_pos_gf = prim_tf_gf.ExtractTranslation() + Gf.Vec3d(0, 0, range_size[2])
    plane_rot_euler_deg = quat_to_euler_angles(np.array(prim_quat_xyzw), degrees=True)
    scatter_plane = rep.create.plane(
        scale=plane_scale, position=plane_pos_gf, rotation=plane_rot_euler_deg, visible=False

    def scatter_pallets():
        pallets2 = rep.create.from_usd(
            prefix_with_isaac_asset_server(PALLET_2_URL), semantics=[("class", "Pallet2")], count=20
        with pallets2:
            rep.randomizer.scatter_2d(scatter_plane, check_for_collisions=True)
        return pallets2.node


Here are some of the unrealistic collisions that has happened that I expect it not to happen. Thanks for any direction.

Currently check_for_collisions=True only considers the scattered objects and not their surroundings.

For such cases, I would recommend using Isaac Sim’s API to spawn/move objects and check for their collisions/overlaps with their surroundings as well.
Example of physx api call for checking for overlaps:

def on_overlap_callback(self, hit):

single_hit_check = False # iterate all overlaping objects
get_physx_scene_query_interface().overlap_box(extent, origin, quat, on_overlap_callback, single_hit_check)

For me and my 3D scatter box my spawned parts were still spawned in another even with check_for_collisions = True, just fyi

Thanks for letting us know, can you provide a short repro script so I can test it and if needed to forward it as a bug?

I did use the “” script and just edited the “rep.randomizer.scatter_2d” function to 3d in line 87and created a cube instead of a plane beforehand with

scatter_box = rep.create.cube(
        scale=0.3, position=(0,0,0.3), visible=False

I just used some YCB Props and dropped them somewhere. They did drop, but while spawning they seemed to be colliding with eachother or get tangled.

I tested with the following script and it works:

import omni.replicator.core as rep

print("No collision check")
spheres = rep.create.sphere(count=200)
volume_torus = rep.create.torus(scale=10, visible=True)
with spheres:
    rep.randomizer.scatter_3d(volume_torus, check_for_collisions=False)
print("Check for collisions")
spheres_2 = rep.create.sphere(count=200)
volume_torus_2 = rep.create.torus(position=(10,10,10), scale=10, visible=True)
with spheres_2:
    rep.randomizer.scatter_3d(volume_torus_2, check_for_collisions=True)

Can you check if you got the following error during scatter, you might be giving too many items to randomize in the volume and the algorithm times out:

[Error] [omni.graph.core.plugin] /Replicator/SDGPipeline/OgnScatter3D_02: Assertion raised in compute - Randomization timed out, cannot find a configuration to randomize prim locations and prevent collisions.

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