Collisions between two OCC objects not reliable

[8bit-Dude]

I have setup a script in which an OCC generated tool moves relative to a box. The box is either generated with ChBodyEasyBox(), or an OCC box converted with ChBodyEasyCascade().

The "EasyBox" produces correct collision counts, but the "OCCBox" does not (it fails to detect collisions with the tool shaft). Here is a sample code, you can switch between chrono and occ box by commenting/uncommenting the system.add() lines:

from pychrono.core import *
from pychrono.cascade import *
ChCollisionModel.SetDefaultSuggestedEnvelope(0.001);
ChCollisionModel.SetDefaultSuggestedMargin(0.001);
material = ChMaterialSurfaceNSC()
tolerance = ChCascadeTriangulateTolerances(0.1 ,True,0.5)

#Create OCC tool
from OCC.Core.BRepPrimAPI import *
from OCC.Core.BRepAlgoAPI import *
sphere = BRepPrimAPI_MakeSphere(2.0).Shape()
cylinder = BRepPrimAPI_MakeCylinder(1.5, 20.0).Shape()
tool = BRepAlgoAPI_Fuse(sphere, cylinder).Shape()
occTool = ChBodyEasyCascade(tool, 1, tolerance, True, material)

#Create OCC box
box = BRepPrimAPI_MakeBox(10.0, 10.0, 2.0).Shape()
occBox = ChBodyEasyCascade(box, 1, tolerance, True, material)
occBox.SetPos(ChVectorD(0.0,0.0,0.0))

#Create CHR box
chrBox = ChBodyEasyBox(10, 10, 2.0, 1, True, True, material)
chrBox.SetPos(ChVectorD(0.0,0.0,0.0))

#Create Physics System (comment/uncomment occBox, chrBox)
system = ChSystemNSC()
system.Add(occTool)
system.Add(occBox) #<- THIS ONE DOES NOT WORK CORRECTLY
#system.Add(chrBox) #<- THIS ONE WORKS CORRECTLY

#Create Viewer for Debugging
from pychrono.irrlicht import *
app = ChIrrApp(system, 'Use OpenCascade shapes', dimension2du(1024,768))
app.AddTypicalSky()
app.AddTypicalLogo(GetChronoDataFile('logo_pychrono_alpha.png'))
app.AddTypicalCamera(vector3df(20,5,5))
app.AddTypicalLights()
app.AssetBindAll();
app.AssetUpdateAll();

#Compute collision state at various positions
from time import *
for z in [15,10,5,0]:
. . . occTool.SetPos(ChVectorD(0,0,z))
. . . system.DoStepDynamics(0)
. . . system.ComputeCollisions()
. . . app.BeginScene(); app.DrawAll(); app.EndScene()
. . . print("Collisions: " + str(system.GetNcontacts()))
. . . sleep(2)

[uebian]

I re-wrote your code using the latest Chrono API, as below:

from pychrono.core import *
from pychrono.cascade import *
ChCollisionModel.SetDefaultSuggestedEnvelope(0.001);
ChCollisionModel.SetDefaultSuggestedMargin(0.001);
material = ChContactMaterialNSC()
tolerance = ChCascadeTriangulate(0.1, True, 0.5)

#Create OCC tool
from OCC.Core.BRepPrimAPI import *
from OCC.Core.BRepAlgoAPI import *
sphere = BRepPrimAPI_MakeSphere(2.0).Shape()
cylinder = BRepPrimAPI_MakeCylinder(1.5, 20.0).Shape()
tool = BRepAlgoAPI_Fuse(sphere, cylinder).Shape()
occTool = ChCascadeBodyEasy(tool, 1, tolerance, True, material)

#Create OCC box
box = BRepPrimAPI_MakeBox(10.0, 10.0, 2.0).Shape()
occBox = ChCascadeBodyEasy(box, 1, tolerance, True, material)
occBox.SetPos(ChVector3d(0.0,0.0,0.0))

#Create CHR box
chrBox = ChBodyEasyBox(10, 10, 2.0, 1, True, True, material)
chrBox.SetPos(ChVector3d(0.0,0.0,0.0))

#Create Physics System (comment/uncomment occBox, chrBox)
system = ChSystemNSC()
system.Add(occTool)
system.Add(occBox) #<- THIS ONE DOES NOT WORK CORRECTLY
#system.Add(chrBox) #<- THIS ONE WORKS CORRECTLY

#Create Viewer for Debugging
from pychrono.irrlicht import *
app = ChVisualSystemIrrlicht()
app.AttachSystem(system)
app.Initialize()
app.AddSkyBox()
app.AddCamera(ChVector3d(0.5,0.1,-0.5))
app.AddTypicalLights()

#Compute collision state at various positions
from time import *
for z in [15,10,5,0]:
    occTool.SetPos(ChVector3d(0,0,z))
    system.DoStepDynamics(0.001)
    app.BeginScene(); app.Render(); app.EndScene()
    print("Collisions: " + str(system.GetNumContacts()))
    sleep(2)

Unfortunately, both ChBodyEasyCascade and ChBodyEasyBox give a collision count of 0. Could you please provide 1. the visualization of the scene, and 2. the expected collision count to help us investigate the issue further?

[stefano2734]

Occt 8.0.0 Final in May or June available.
Actual pre release RC5 with about 400 fixes to used 7.9.2 here.
https://github.com/Open-Cascade-SAS/OCCT/releases
Perhaps the problem is better possible to solve with this new major release.