development/tutorial_pychrono_demo_mesh.html

#------------------------------------------------------------------------------

# Name:        pychrono example

# Purpose:

#

# Author:      Alessandro Tasora

#

# Created:     1/01/2019

# Copyright:   (c) ProjectChrono 2019

#------------------------------------------------------------------------------


import pychrono.core as chrono

import pychrono.irrlicht as chronoirr


print ("Example: create a rigid body based on a .obj mesh file");


# The path to the Chrono data directory containing various assets (meshes, textures, data files)

# is automatically set, relative to the default location of this demo.

# If running from a different directory, you must change the path to the data directory with:

#chrono.SetChronoDataPath('path/to/data')


# ---------------------------------------------------------------------

#

#  Create the simulation system and add items

#


mysystem      = chrono.ChSystemNSC()


# Set the global collision margins. This is expecially important for very large or

# very small objects. Set this before creating shapes. Not before creating mysystem.

chrono.ChCollisionModel.SetDefaultSuggestedEnvelope(0.001);

chrono.ChCollisionModel.SetDefaultSuggestedMargin(0.001);


# ---------------------------------------------------------------------

#

#  Create the simulation system and add items

#


# Create a contact material (with default properties, shared by all collision shapes)

contact_material = chrono.ChMaterialSurfaceNSC()


# Create a floor

mfloor = chrono.ChBodyEasyBox(3, 0.2, 3, 1000,True,True, contact_material)

mfloor.SetBodyFixed(True)

mysystem.Add(mfloor)


# Now we will create a falling object whose shape is defined by a .obj mesh.

#

# NOTE: collision detection with generic concave meshes is slower and less

# robust than any other options for collision shapes, so use it if defining

# collision shapes via primitives like spheres boxes cylinders or their

# clusters is too complex.

#

# NOTE: the mesh shape is a .obj file in Wavefront file format,

# you can generate it from 3D modelers such as Blender, Maya, etc.

#

# NOTE: for collision purposes, the .obj mesh must be "watertight", i.e. having

# no gaps in edges, no repeated vertexes, etc.

#

# NOTE: for visualization purposes only, i.e. if you do not use the mesh also for

# collision, the mesh does not need to be watertight.


# Method A:

# - use the ChBodyEasyMesh

# This will automatically create the visualization mesh, the collision mesh,

# and will automatically compute the mass property (COG position respect to REF,

# mass and inertia tensor) given an uniform density.


body_A= chrono.ChBodyEasyMesh(chrono.GetChronoDataFile('shoe_view.obj'), # mesh filename

                              7000, # density kg/m^3

                              True, # automatically compute mass and inertia

                              True, # visualize?>

                              True, # collide?

                              contact_material,

                              ) # use mesh for collision?

body_A.SetPos(chrono.ChVectorD(0.5,0.5,0))

mysystem.Add(body_A)


# Method B:

# - create a ChBodyAuxRef,

# - set mass and inertia tensor as you like

# - set COG center of mass position respect to REF reference as you like

# - attach a visualization shape based on a .obj triangle mesh

# - add contact shape based on a .obj triangle mesh

# This is more complicate than method A, yet this can be still preferred if you

# need deeper control, ex. you want to provide two different meshes, one

# with high level of detail just for the visualization and a coarse one for

# collision, or if you want to set custom COG and inertia values, etc.


# Rigid body part

body_B= chrono.ChBodyAuxRef()

body_B.SetPos(chrono.ChVectorD(0,0.5,0))

body_B.SetMass(16)

body_B.SetInertiaXX(chrono.ChVectorD(0.270,0.400,0.427))

body_B.SetInertiaXY(chrono.ChVectorD(0.057,0.037,-0.062))

body_B.SetFrame_COG_to_REF(chrono.ChFrameD(

            chrono.ChVectorD( 0.12,0.0,0),

            chrono.ChQuaternionD(1,0,0,0)))


# Attach a visualization shape .

# First load a .obj from disk into a ChTriangleMeshConnected:

mesh_for_visualization = chrono.ChTriangleMeshConnected()

mesh_for_visualization.LoadWavefrontMesh(chrono.GetChronoDataFile('shoe_view.obj'))

# Optionally: you can scale/shrink/rotate the mesh using this:

mesh_for_visualization.Transform(chrono.ChVectorD(0.01,0,0), chrono.ChMatrix33D(1))

# Now the  triangle mesh is inserted in a ChTriangleMeshShape visualization asset,

# and added to the body

visualization_shape = chrono.ChTriangleMeshShape()

visualization_shape.SetMesh(mesh_for_visualization)

body_B.AddAsset(visualization_shape)


# Add the collision shape.

# Again load a .obj file in Wavefront file format. NOTE: in this

# example we use the same .obj file as for visualization, but here one

# could do a better thing: using a different low-level-of-detail mesh for the

# collision, so the simulation performance is not affected by many details such

# as bolts and chamfers that may be wanted only for visualization.

mesh_for_collision = chrono.ChTriangleMeshConnected()

mesh_for_collision.LoadWavefrontMesh(chrono.GetChronoDataFile('shoe_view.obj'))

# Optionally: you can scale/shrink/rotate the mesh using this:

mesh_for_collision.Transform(chrono.ChVectorD(0.01,0,0), chrono.ChMatrix33D(1))

body_B.GetCollisionModel().ClearModel()

body_B.GetCollisionModel().AddTriangleMesh(

            contact_material, # contact material

            mesh_for_collision, # the mesh

            False,  # is it static?

            False)  # is it convex?

            # , mpos, mr,  # pos of mesh respect to REF and rotation matr.respect to REF

            # 0.01) # 'inflating' radiust for triangles for increased robustness

body_B.GetCollisionModel().BuildModel()

body_B.SetCollide(True)


mysystem.Add(body_B)


# ---------------------------------------------------------------------

#

#  Create an Irrlicht application to visualize the system

#


myapplication = chronoirr.ChIrrApp(mysystem, 'PyChrono example', chronoirr.dimension2du(1024,768))


myapplication.AddTypicalSky()

myapplication.AddTypicalLogo(chrono.GetChronoDataFile('logo_pychrono_alpha.png'))

myapplication.AddTypicalCamera(chronoirr.vector3df(0.5,0.5,1), chronoirr.vector3df(0,0,0))

#myapplication.AddTypicalLights()

myapplication.AddLightWithShadow(chronoirr.vector3df(3,6,2),    # point

                                 chronoirr.vector3df(0,0,0),    # aimpoint

                                 12,                 # radius (power)

                                 1,11,              # near, far

                                 55)                # angle of FOV


            # ==IMPORTANT!== Use this function for adding a ChIrrNodeAsset to all items

            # in the system. These ChIrrNodeAsset assets are 'proxies' to the Irrlicht meshes.

            # If you need a finer control on which item really needs a visualization proxy in

            # Irrlicht, just use application.AssetBind(myitem); on a per-item basis.


myapplication.AssetBindAll();


            # ==IMPORTANT!== Use this function for 'converting' into Irrlicht meshes the assets

            # that you added to the bodies into 3D shapes, they can be visualized by Irrlicht!


myapplication.AssetUpdateAll();


            # If you want to show shadows because you used "AddLightWithShadow()'

            # you must remember this:

myapplication.AddShadowAll();


# ---------------------------------------------------------------------

#

#  Run the simulation

#


myapplication.SetTimestep(0.005)


while(myapplication.GetDevice().run()):

    myapplication.BeginScene()

    myapplication.DrawAll()

    myapplication.DoStep()

    myapplication.EndScene()