[Opensim-dev] Using ODE for vehicles and ragdolls

Sat Nov 22 10:58:34 UTC 2008

Hello N Lin,

Great work!! Going to try that later on today and let you know about
how it went.

Rhian

On Fri, Nov 21, 2008 at 3:12 PM, nlin (message) <nlin.message at gmail.com> wrote:
> Hello,
>
> Great to see all of the work on and interest in vehicles and ODE in
> OpenSim. I have posted a highly experimental patch to enable jointed
> ODE vehicles, based off of r7394. The project is on GForge here:
>
> http://forge.opensimulator.org/gf/project/physicsjoints/
>
> Though this patch is nowhere near complete, I thought it might help
> the discussion by providing an illustrative example of a working
> prototype implementation of jointed ODE vehicles in OpenSim.
>
> Please have a look if you are interested; feedback and discussion
> would be most welcome.
>
> Thanks,
> N Lin (nlin)
>
>
> 2008/11/19, James Stallings II <james.stallings at gmail.com>:
>> Heh.
>>
>> For the record:
>>
>> It was I who first demostrated the possibility of using
>> llSetForce/llApplyImpulse as a viable method of making a prim behave like a
>> vehicle, some 10 months or so ago. During a conversation with one Owen Oyen
>> (who is something of a physics guy), of SL and OSGrid, he became aware of my
>> proof-of-concept efforts along these lines and produced a working vehicle
>> script.
>>
>> On the linden grid, Owen is a boat scripter and scripter of related
>> technologies; he has, for instance, devised a means of producing current
>> effects based on a model of the contour of the sea floor
>>
>> While our current work is targeted directly at boating, it can be readily
>> adapted to encompass all of the typical vehicle types of SL, without any of
>> their vehicle functions.
>>
>> This model is very primitive, as are those presented in the LSL Vehicle API
>> as found in LL's LSL.
>>
>> The characteristics of the LSL vehicle API as implemented by LL are quite
>> simple:
>>
>> 1. Linear motors. These motors provide motive force parallel to a given axis
>> or axes.
>> 2. Torque motors. These motors provide rotational force about an axis or
>> axes.
>>
>> That's it. Period.
>>
>> These two models are further modified by a series of contraints that
>> introduce the concept of friction or other load against the forces provided
>> by these motors.
>>
>> Tidy all this up into a 32 bit bitfield for describing the motive forces and
>> their loads and wrap it up in a nice set of functions exposing this via LSL
>> commands that characterise a vehicle 'type' (e.g., boat/car/plane) with any
>> related constraints/dampers and you have Linden vehicle physics.
>>
>> As I said, this is a highly simplified vehicle simulation model. There is no
>> distribution of mass involved, no geometry-based drag. There is a single
>> center of gravity at the geometric center. All motion produced by the calls
>> to the API is produced around this center. The complexity all rests witth
>> the description of the motive forces and their respective loading and
>> damping. The forces are applied either to a simple prim in the simplest
>> case, or to a linkset. If to a linkset, the linkset is treated as a single
>> object except for collision purposes, the extent of which is to mesh any
>> geometric complexities of the object.
>>
>> The short story is, we have modelled LSL-style vehicles using little but
>> llApplyImpulse and llSetForce, and a first-order friction calculation.
>> Ironically, our experiences indicate that these vehicles are consistently
>> better in their handling characteristics than what is available on the
>> Linden grid. Indeed, about half of Owen's current work is in the interest of
>> porting this work *back* to the linden grid.
>>
>> Enough of that. Lets talk ODE :D
>>
>> ODE *does* present some rich opportunities for simulation beyond the
>> (arguably oversimplified) model presented by the LSL vehicle API. given the
>> type of things I've seen reading the ODE documentation, my suspicion is that
>> it's strong points for such simulations will be wheeled vehicles, tracked
>> vehicles, walkers, and by extension, ragdoll/skeletal physics. These would
>> certainly add an interesting element to the mix, and I am all for seeing
>> these ideas roll forward.
>>
>> I do, however, wish to draw a strong distinction between this ODE work and
>> basic vehicle physics ala Linden Labs, as the vehicle paradigm in LSL is so
>> heavily abstracted that 'simulation', for any meaningful employment of the
>> word, is at best inaccurate, and at most hype. Worse, their method of
>> 'simplifying' (read 'dumbing down'), adds significant processing cycles;
>> were I to guess, I'd say that their API represents greater processing
>> overhead than do the physics proper.
>>
>> I'd say +1 for rolling forward with some OS functions for ODE; indeed, I
>> would suggest (as I have been for some 9 months now) that ODE's interface be
>> exposed directly in a set of OS functions, allowing the scripter to work in
>> a relationship that is only once removed from the physics engine, in the
>> interest of providing the fullness of the ODE featureset to the scripter. I
>> think some fabulously interesting things would come of this, not the least
>> of which might be a more interesting in-world experience for those of us who
>> primarily employ this as an entertainment platform.
>>
>> Keep up the good work y'all, this is an excellent dialogue and I hope I have
>> contributed in some way to a clarification of the events surrounding our
>> recent in-world vehicle work (btw we should be ready to demo some of this
>> broadly this coming weekend), and to the issues that lie ahead as we work to
>> bring more physics features to the scripting language and our virtual
>> environment.
>>
>>
>> Cheers!
>> Hiro/daTwitch/Laz...etc.
>>
>>
>>
>> On Wed, Nov 19, 2008 at 6:14 AM, Stefan Andersson
>> <stefan at tribalmedia.se>wrote:
>>
>>>  I for one would love to see it unfold something like this
>>>
>>> 1) one or several prototypical and specialized implementations coding
>>> directly to ODE but in a nice manner.
>>> 2) the implementations refactored into a nice OpenSim API for ODE joints
>>> 3) one or several implementations of vehicles utilizing this API directly
>>> 4) these implementations refactored into a nice OpenSim vehicle API
>>> 5) implementing the LSL vehicle model using this API
>>>
>>> so yeah, bottom up is the way to go, but with a clear goal in the back of
>>> our heads.
>>>
>>> I for one would want to see the monorail module before the monorail lsl
>>> script.
>>>
>>> I also suspect that along the lines, we might see that we want to
>>> implement
>>> vehicle types that don't fit into the lsl model... like the 'humanoid' or
>>> 'animal' - anybody up for building a stone giant or re-casting an agent in
>>> pure prims? :D
>>>
>>> Best regards,
>>> Stefan Andersson
>>> Tribal Media AB
>>>
>>> Join the 3d web revolution : http://tribalnet.se/
>>>
>>>
>>>
>>>
>>>
>>> > From: adam at deepthink.com.au
>>> > To: opensim-dev at lists.berlios.de
>>> > Date: Wed, 19 Nov 2008 02:01:27 -0500
>>>
>>> > Subject: Re: [Opensim-dev] Using ODE for vehicles and ragdolls
>>> >
>>> > Doesnt ODE have vehicle support internally? The concern I'd have about a
>>> vehicle layer over the top might be that performance is suboptimal since
>>> we
>>> need to run a second physics step which could introduce issues.
>>> >
>>> > Regards,
>>> >
>>> > Adam
>>> >
>>> > > -----Original Message-----
>>> > > From: opensim-dev-bounces at lists.berlios.de [mailto:opensim-dev-
>>> > > bounces at lists.berlios.de] On Behalf Of Gerhard Dünnebeil
>>> > > Sent: Tuesday, 18 November 2008 10:40 PM
>>> > > To: opensim-dev at lists.berlios.de
>>> > > Subject: Re: [Opensim-dev] Using ODE for vehicles and ragdolls
>>> > >
>>> > > Hi
>>> > >
>>> > > having looked into the ODE engine I don't think it's usable for the
>>> > > vehicle API.
>>> > >
>>> > > Instead i think we should put the vehicle engine on top of it.
>>> > >
>>> > > This is pretty easily done by adding another layer (could/should be in
>>> > > a
>>> > > plugin).
>>> > > It can be called in each "Simulate" step and calculate the forces
>>> > > needed
>>> > > to achieve the vehicles behaviour.
>>> > > These forces are then applied -- using the phys engine's API -- to the
>>> > > objects.
>>> > >
>>> > > This way we are
>>> > > a) ... independant (at least theoretically) from the characteristics
>>> > > of
>>> > > the underlying Phys engine
>>> > > b) ... able to implement different engines for different purposes
>>> > >
>>> > > I know someone (is it you, nlin?) already implemented a sailing boat
>>> > > in
>>> > > OpenSim. A modular approach here would allow us to implement
>>> > > alternative
>>> > > friction models beyond what LSL gives us.
>>> > >
>>> > >
>>> > > Just my two cents
>>> > >
>>> > > Gerhard
>>> > >
>>> > >
>>> > > nlin (message) wrote:
>>> > > > Hello,
>>> > > >
>>> > > > There's been some discussion about SL-compatible vehicles in OpenSim
>>> > > > recently, with its higher-level abstraction of how vehicles work.
>>> > > This
>>> > > > would have the long-term goals of compatibility and ability to swap
>>> > > > out physics engines while still using the same vehicle layer.
>>> > > >
>>> > > > SL-compatibility and abstracting vehicles from the physics engine
>>> > > > are
>>> > > > good goals for the long term; sort of a top-down approach (start
>>> > > > with
>>> > > > the vehicle abstraction, map it to many different physics engines).
>>> > > >
>>> > > > Complementary to this, I'd like to explore and start discussion of
>>> > > > an
>>> > > > alternative way of handling vehicles by using a bottom-up approach.
>>> > > > Starting with the specific physics engine of ODE, can we use
>>> > > > ODE-specific features to make simple vehicles?
>>> > > >
>>> > > > I did some experiments with OpenSim and ODE and the answer seems to
>>> > > be
>>> > > > yes, we can make simple vehicles with ODE by using joints. We can
>>> > > also
>>> > > > make ragdolls. I posted some videos to YouTube of the preliminary
>>> > > results:
>>> > > >
>>> > > > http://www.youtube.com/watch?v=iYIh-eIwmjs
>>> > > > http://www.youtube.com/watch?v=z9bedzIuxdM
>>> > > >
>>> > > > This is only prototype work for now, put together sort of quickly as
>>> > > a
>>> > > > proof-of-concept with just enough "plumbing" (data flow) to work.
>>> > > > There are a number of issues that need to be solved for this to work
>>> > > > cleanly. As far as I know (please correct me if I'm wrong) there
>>> > > > hasn't been much work done to try to get ODE
>>> > > > joints/vehicles/ragdolls
>>> > > > working in OpenSim, but I think it's an avenue worth exploring.
>>> > > >
>>> > > > Is there interest in pursuing this approach for OpenSim vehicles? I
>>> > > > would look forward to discussing some of the issues that would need
>>> > > to
>>> > > > be solved.
>>> > > >
>>> > > > Thanks,
>>> > > > N Lin (nlin)
>>> > > >
>>> > > > ---------------------------------------------------------------------
>>> > > ---
>>> > > >
>>> > > > _______________________________________________
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>>> > > >
>>> > >
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>>
>>
>> --
>> ===================================
>> The wind
>> scours the earth for prayers
>> The night obscures them
>>
>> http://osgrid.org
>> http://del.icio.us/SPQR
>> http://twitter.com/jstallings2
>> http://www.linkedin.com/pub/5/770/a49
>>
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