Dectecting and saving contact points in collision Pychrono

[Declan Mulroy]

Hello, 

Ive managed to collect and save Forces generated by collision however Im also trying to save the locations of those points of contact in the global frame using pychrono. I found this function in the core.py code but am not sure what it wants. Does it want the coordinate frame of the local object and global object or is this not even the correct function to use. I am also using EasyBodycylinders as well. 

   def GetContactPoint(self, loc_point, state_x):

        r"""GetContactPoint(ChBody self, ChVectorD loc_point, ChState state_x) -> ChVectorD"""

        return _core.ChBody_GetContactPoint(self, loc_point, state_x)

Thank you in advanced, 

Declan Mulroy

[Radu Serban]

Hi Declan,

That function (and several more) should not be in the public API -- they implement the interface to so-called ChContactable objects (objects that can generate contacts).  I will clean this up when I get a chance.

To report contact point locations use the contact reporting callback mechanism, by deriving your own reporter from ChContactContainer::ReportContactCallback.
See demo_python_2.py for an example and the documentation at (http://api.projectchrono.org/development/classchrono_1_1_ch_contact_container_1_1_report_contact_callback.html)

--Radu

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[Declan Mulroy]

I see. Thank Radu!

On Friday, November 15, 2019 at 1:40:21 AM UTC-6, Radu Serban wrote:

Hi Declan,

That function (and several more) should not be in the public API -- they implement the interface to so-called ChContactable objects (objects that can generate contacts).  I will clean this up when I get a chance.

To report contact point locations use the contact reporting callback mechanism, by deriving your own reporter from ChContactContainer::ReportContactCallback.
See demo_python_2.py for an example and the documentation at (http://api.projectchrono.org/development/classchrono_1_1_ch_contact_container_1_1_report_contact_callback.html)

--Radu

On 11/15/2019 12:46 AM, Declan Mulroy wrote:

Hello, 

Ive managed to collect and save Forces generated by collision however Im also trying to save the locations of those points of contact in the global frame using pychrono. I found this function in the core.py code but am not sure what it wants. Does it want the coordinate frame of the local object and global object or is this not even the correct function to use. I am also using EasyBodycylinders as well. 

   def GetContactPoint(self, loc_point, state_x):

        r"""GetContactPoint(ChBody self, ChVectorD loc_point, ChState state_x) -> ChVectorD"""

        return _core.ChBody_GetContactPoint(self, loc_point, state_x)

Thank you in advanced, 

Declan Mulroy

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[Declan Mulroy]

Hello Again, 

I went though the python_2.py demo and have been working off of that however im trying to be able to call on the point vA but it will not allow me to. I tried inserting an empty array but it was not working as well as have it return the variable vA which is the contact point location. 

How would I extract the contact point locations from the class or from the function getcontactcontainer in general. Below is the modified code I am working with which is essentialy python_2.py tutorial. 

Thank you in advanced,

Declan. 

class MyReportContactCallback(chrono.ReportContactCallback):

    def __init__(self):

         chrono.ReportContactCallback.__init__(self)

         

#    def OnReportContact(self,vA,vB,cA,dist,rad,force,torque,modA,modB):

#        

##        bodyUpA = chrono.CastContactableToChBody(modA)

##         nameA = bodyUpA.GetName()

##         bodyUpB = chrono.CastContactableToChBody(modB)

##         nameB = bodyUpB.GetName()

##         print ('  contact: point A=' , vA,  '  dist=',dist, 'Body A:', nameA, 'Body B:', nameB)

#        return True        # return False to stop reporting contacts

    def OnReportContact(self,vA,vB,cA,dist,rad,force,torque,modA,modB):

        

#        bodyUpA = chrono.CastContactableToChBody(modA)

#         nameA = bodyUpA.GetName()

#         bodyUpB = chrono.CastContactableToChBody(modB)

#         nameB = bodyUpB.GetName()

#         print ('  contact: point A=' , vA,  '  dist=',dist, 'Body A:', nameA, 'Body B:', nameB)

          return vA        # return False to stop reporting contacts

#

my_rep = MyReportContactCallback()

# Simulation loop

my_system.SetChTime(0)

while (my_system.GetChTime() < 1.2) :

    my_system.DoStepDynamics(0.01)

 #   print ('time=', my_system.GetChTime(), ' bodyB y=', my_shbodyB.GetPos().y)

    my_system.GetContactContainer().ReportAllContacts(my_rep)

On Friday, November 15, 2019 at 1:40:21 AM UTC-6, Radu Serban wrote:

Hi Declan,

That function (and several more) should not be in the public API -- they implement the interface to so-called ChContactable objects (objects that can generate contacts).  I will clean this up when I get a chance.

To report contact point locations use the contact reporting callback mechanism, by deriving your own reporter from ChContactContainer::ReportContactCallback.
See demo_python_2.py for an example and the documentation at (http://api.projectchrono.org/development/classchrono_1_1_ch_contact_container_1_1_report_contact_callback.html)

--Radu

On 11/15/2019 12:46 AM, Declan Mulroy wrote:

Hello, 

Ive managed to collect and save Forces generated by collision however Im also trying to save the locations of those points of contact in the global frame using pychrono. I found this function in the core.py code but am not sure what it wants. Does it want the coordinate frame of the local object and global object or is this not even the correct function to use. I am also using EasyBodycylinders as well. 

   def GetContactPoint(self, loc_point, state_x):

        r"""GetContactPoint(ChBody self, ChVectorD loc_point, ChState state_x) -> ChVectorD"""

        return _core.ChBody_GetContactPoint(self, loc_point, state_x)

Thank you in advanced, 

Declan Mulroy

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[Radu Serban]

 

Hi Declan,

 

I am not perfectly clear on what you mean by being “able to call on the point vA”, but you cannot have OnReportContact return it.  That method is called internally by ReportAllContacts and must return ‘true’ or ‘false’, informing the caller (ReportAllContacts) to continue processing the next contact or stop processing, respectively.

 

If you want to extract all vA points in a list, you can do something like:

 

class MyReportContactCallback(chrono.ReportContactCallback):

    def __init__(self):

        chrono.ReportContactCallback.__init__(self)

        self.points = []

    def OnReportContact(self,vA,vB,cA,dist,rad,force,torque,modA,modB):

        self.points.append(vA)

        return True        # return False to stop reporting contacts

    def ResetList(self):

        self.points = []

    def GetList(self):

        return self.points

 

my_rep = MyReportContactCallback()

 

while (my_system.GetChTime() < 1.2) :

    my_system.DoStepDynamics(0.01)

 

    my_rep.ResetList()

    my_system.GetContactContainer().ReportAllContacts(my_rep)

    crt_list = my_rep.GetList()

    print('time=', my_system.GetChTime(), ' num. contacts=', my_system.GetContactContainer().GetNcontacts())

    print(*crt_list, sep='\n')

 

Is this what you need?

--Radu

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[Declan Mulroy]

Yes That's exactly what I am looking for. To extract the points of contact and which bodies made contact. Thank you Radu!

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Declan Mulroy
Direct: (847)-767-3222
Mechanical Engineering | Armour College of Engineering

Illinois Institute of Technology

[Qihan Xuan]

Hi,

Is it doable to write this code as C++?

Thanks,

Qihan

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[Radu Serban]

Qihan,

Look at demo_IRR_callbackNSC (https://github.com/projectchrono/chrono/blob/develop/src/demos/irrlicht/demo_IRR_callbackNSC.cpp) and demo_IRR_callbackSMC (https://github.com/projectchrono/chrono/blob/develop/src/demos/irrlicht/demo_IRR_callbackSMC.cpp) for C++ examples of using contact reporting callbacks.

--Radu

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