What's the difference between the RGB-frame and the white point when visualize my MechanicalObject?

[TurboS2002]

Hi everyone!
I'm trying to generate a line segment using RegularGridTopology, add a MechanicalObject to the segment, and a collision model.
The point with index 0 of this line segment is connected to a point on another moving object using a BilateralInteractionConstraint, in order to keep the line segment and the collision model relatively stationary with the object.
However, when I ran the simulation I found that the line segment would not move with the other object, and that the point on the other object would not move as it normally would, probably due to the BilateralInteractionConstraint.
I have noticed that when I visualise the MechanicalObject of this line segment via showObject='1', it shows a series of white dots instead of RGB coordinates, which is different from normal, so I'm wondering if I'm doing something wrong here.
So I was wondering what's the difference between the RGB-frame and the white point when visualise my MechanicalObject? and if you have any good suggestions to achieve my goal?

Thanks !

[hugtalbot]

Hi @TurboS2002

• When the MechanicalObject has a template="Vec3d" it corresponds to a soft body (i.e. deformable), in this case the degrees of freedom appear as white dots when activating showObject=True
• When the MechanicalObject has a template="Rigid3d" it corresponds to a rigid body, in this case the degrees of freedom appear as a frame (RGB looking) when activating showObject=True

I hope it clarifies things.
Best

[TurboS2002]

Thank you! You have made it very clear.

My other problem is that I created a straight line through the

line.addObject('RegularGridTopology', name="lineTopo", nx="20", ny="1", nz='1', min='0.0 0.0 0.0', max=str(ray_length) + ' 0.0 0.0')
line.addObject('LineCollisionModel', group='1', simulated="1", contactStiffness="1")

My aim is to connect this straight line to a point on another object and that line can move with that object.

I have tried both BilateralInteractionConstraint as well as AttachConstraint for this purpose and the result is that the line is stationary and does not move with the object. I am connecting the points with index 0 in the line as well as the points with index 0 in the object, and the initial effect is as follows

With BilateralInteractionConstraint, the points on the object also become stationary.

With AttachConstraint, the object moves normally, but the line does not move with the object.

Can you provide some suggestions for achieving this?

[hugtalbot]

Hi @TurboS2002

For me to better understand, do you have a description of what you want to simulate more precisely : what is this straight line, to what object is it attached?

For an attachment to work, you need to have a MechanicalObject storing the degrees of freedom.
Do not hesitate to share a minimalist scene example.

Hope this helps

[hugtalbot]

Attaching two objects can indeed be done either using:

• a BilateralInteractionConstraint (BilateralLagrangianConstraint) formulating the attachment as a constraint
• AttachConstraint (AttachProjectiveConstraint) projecting the constraint at the end of the time step
• or using springs

Could you share your scene @TurboS2002 ?

[github-actions[bot]]

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@TurboS2002
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