Re: [Assimp-discussions] Animating a robot arm

[Francesco C. <f.c...@gm...>]

Thanks again for your answer. I was thinking, though:
1) skeletal animation does not preserve "rigid" elements in any way, am I
right? Although it appears to me to be perfect for animating general meshes
(game characters and so on) I can't see how this could be the most
straightforward approach for what concerns rigid bodies
2) as an alternative approach, what about loading all the pieces of my
robot arm as separate meshes (but in the same scene) and then transform
them according to the kinematic equations of the arm? I think this is a
viable option, am I right? How dows assimp helps in this case?

Thanks


2014-06-03 18:14 GMT+02:00 Chananya Freiman <spe...@gm...>:

> That is correct.
>
> Skeletal animation by itself is a very simple concept, read on it on wiki
> or other sources. The implementation is also very simple, as long as you
> know your way around matrices and vector transformations (and if you don't,
> this is a good time to start reading!)
>
>
> On Tue, Jun 3, 2014 at 7:09 PM, Francesco Corucci <f.c...@gm...>
> wrote:
>
>> Thank you Chananya. So if my understanding is correct, what I have to do
>> is to bring the model into another software more suitable for animation
>> (such as blender), define the skeleton there, export the model in one of
>> the formats supported by assimp, and try do do skeletal animation in my
>> code exploiting assimp.
>> Am I right?
>>
>> Thank you very much again
>>
>> Francesco
>>
>>
>>
>> 2014-06-03 17:54 GMT+02:00 Chananya Freiman <spe...@gm...>:
>>
>>  tl:dr answer: yes, skeletal animations are what you want.
>>>
>>> Long answer:
>>> There are two common (are there others?) ways to animate things. Vertex
>>> animations, and skeletal animations.
>>> Vertex animations means you hold N frames of your whole geometry, and
>>> you just select the correct one. This uses a lot of memory, but requires no
>>> processing at real-time.
>>> Skeletal animations uses matrices in a hierarchy representing your
>>> model's "skeleton", and every vertex has information as to what matrices
>>> affect it, and how much they affect it (by using weights). This requires
>>> only a single frame of your geometry, which is usually called the bind pose
>>> (but many people call it in many different names, go figure), but it
>>> requires processing at real-time to do many matrix-vector multiplications.
>>>
>>> These days the concept of vertex animations is almost never used for two
>>> reasons:
>>> 1) They consume way too much memory. Imagine a 20K triangle mesh
>>> duplicated over thousands of frames.
>>> 2) The cost of running skeletal animation is negligible when running on
>>> the GPU, unlike olden days when it ran on the CPU and took a considerate
>>> chunk of the frame time.
>>>
>>> That said, vertex animations still exist on low-end platforms such as
>>> simple phones that don't support OpenGL ES 2, where you can't use shaders,
>>> and thus can't run it on the GPU. In this case, especially with the weak
>>> processors these platforms have, the cost of running skeletal animations
>>> might be greater than the cost of consuming more memory, especially since
>>> most of the models on said platforms are really low poly and have very
>>> little frames to begin with.
>>>
>>> ------
>>>
>>> Now, as to how to actually get this done, SolidWorks doesn't support any
>>> kind of animation (beside really primitive key'ing), so you will need to
>>> export your model to a modeling software (e.g. 3ds Max, Blender) and
>>> finalize the model there.
>>>
>>>
>>> On Tue, Jun 3, 2014 at 6:17 PM, Francesco Corucci <f.c...@gm...>
>>> wrote:
>>>
>>>> Hi guys,
>>>>
>>>> I have a Solid Works model of a robot arm, and I would like to be able
>>>> to set joint positions in order to move the arm in assimp. Particularly,
>>>> the arm features some pistons (linear actuators) as well as some rotational
>>>> joints.
>>>>
>>>> Concerning animation in assimp, I've read something related to skeletal
>>>> animation.
>>>> Is this the way to do what I want to do (move rigid parts connected by
>>>> joints) or there is a better/simpler way? Skeletal animation seems to do a
>>>> harder work with respect to what I need.
>>>>
>>>> Also, should the CAD model feature something particular in order to
>>>> make this kind of animation possible? Should I work with specific formats
>>>> in order to be able to do this?
>>>>
>>>> Could you please provide some hints? I am very new to this stuff
>>>>
>>>> Every suggestion/comment is highly appreciated
>>>>
>>>> Thank you,
>>>>
>>>> Francesco
>>>>
>>>>
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>>
>