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Flightgear-devel mailing list
Jon Berndt [EMAIL PROTECTED] said:
[to Jim, in particular]
I have added code in JSBSim that calculates the relative position in local
frame (world space, in units of feet) of the common Visual Reference Point
(VRP) with respect to the current CG. The nest thing I have to do is to
modify
PROTECTED] Behalf Of Jim Wilson
Sent: Friday, January 16, 2004 7:35 PM
To: FlightGear developers discussions; Jon Berndt
Subject: RE: [Flightgear-devel] 3D aircraft model origins
Jon Berndt [EMAIL PROTECTED] said:
[to Jim, in particular]
I have added code in JSBSim that calculates the relative
On Monday, 12 January 2004 01:05, Jon Berndt wrote:
It's done. Beta version, anyhow. See the announcement in the JSBSim list.
Jon
Excellent!
Now go spend some time with your kids Jon. ;)
What would be really useful and helpful is a step-by-step tutorial for the
layman of how to configure an
On Mon, 12 Jan 2004 21:38:06 +0200
Paul Surgeon [EMAIL PROTECTED] wrote:
Excellent!
Now go spend some time with your kids Jon. ;)
No kidding. Tonight is library night, so I will be spending some
time with the older ones. :-)
What would be really useful and helpful is a step-by-step tutorial
I've been watching this thread with some interest. May I say how impressed I
am with all that has been achieved so far.
FWIW I thought I describe my experience of modelling a 3d aircraft. At the
outset I used the nose as the origin of both the model and the FDM (YASIM in
this case). The 3d
Innis Cunningham [EMAIL PROTECTED] said:
Take Lee's P51 it has its MRP at the nose.
That's mine :-)
It is my understanding that the offset system was devised primarily to allow
MSFS A/C
to be positioned correctly.
The model offsets yes. The view offsets no.
I stand corrected if this is
Innis Cunningham [EMAIL PROTECTED] said:
All the model is is 1 vertices flying in close formation
Haha! That's about it for some of my modeling work. Gotta try and keep that
vertex count down :-)
Best,
Jim
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Lee Elliott [EMAIL PROTECTED] said:
How about the frontmost point on the leading edge of the main-wings at the
root - or would that be snafu'd by LEXs? e.g. F-18. Could be a bit iffy on
I think that actually would be the nose on a space shuttle model. ;-) One
question that came up before
Jon S Berndt [EMAIL PROTECTED] said:
I have still not delivered on my promise to provide the reference
point to FlightGear. I don't know what we do for the C-172, in order
to place it correctly.
Any chance that would be happening soon?
Best,
Jim
It's in work at this instant
[to Jim, in particular]
I have added code in JSBSim that calculates the relative position in local
frame (world space, in units of feet) of the common Visual Reference Point
(VRP) with respect to the current CG. The nest thing I have to do is to
modify the lat/lon/alt that the FDM owns. The VRP
Any chance that would be happening soon?
Best,
Jim
It's in work at this instant and nearly complete.
Jon
It's done. Beta version, anyhow. See the announcement in the JSBSim list.
Jon
--
Project Coordinator
JSBSim Flight Dynamics Model
http://www.jsbsim.org
Sorry Jim.
Jim Wilson writes
Innis Cunningham [EMAIL PROTECTED] said:
Take Lee's P51 it has its MRP at the nose.
That's mine :-)
Jim
_
E-mail just got a whole lot better. New ninemsn Premium. Click here
On Sunday 11 January 2004 15:58, Jim Wilson wrote:
Innis Cunningham [EMAIL PROTECTED] said:
Take Lee's P51 it has its MRP at the nose.
That's mine :-)
I missed that - Yes, its definitely one of Jims.
LeeE
It is my understanding that the offset system was devised primarily to
allow
Surely that's an approximation, no? A rigid body's response to a
(force + torque) moment has 7 degrees of freedom (one value for mass,
and a 6DOF inertia tensor). A single offset doesn't have enough
complexity to capture that behavior.
Andy
The rigid body response to a force and torque
On Saturday 10 January 2004 03:09, Jon Berndt wrote:
Paul:
The root of the problem - though it is not really a problem - is that the
FDM cares about modeling where the aircraft is in the world based on the
aircraft CG, and the 3D model wants to be in the correct spot in the world,
too, but
On Saturday 10 January 2004 02:35, Jim Wilson wrote:
Paul Surgeon [EMAIL PROTECTED] said:
On Saturday, 10 January 2004 00:35, Erik Hofman wrote:
No, sorry. AC_EARORP is the published offset from CG to where the
forces act. For the F-16 that would be 35% chord (and CG is 25% chord).
Perhaps some published 'Standards' might be a good idea - I remember the
earlier discussions about the model origin but didn't realise
that a standard
had been established, and so in ignorance, I haven't been following it:(
I'm working on it.
Jon S. Berndt wrote:
The rigid body response to a force and torque can be in roll, pitch,
yaw, and/or X, Y, Z translation. That's six DoF. How does the
seventh degree come into play?
I wasn't clear: the rigid body response function takes a 6DOF space
(force + torque) to another 6DOF space
On Saturday 10 January 2004 15:23, Jon Berndt wrote:
Perhaps some published 'Standards' might be a good idea - I remember the
earlier discussions about the model origin but didn't realise
that a standard
had been established, and so in ignorance, I haven't been following it:(
I'm working
Jim Wilson wrote:
That is mostly correct. There is also a visual effect that occurs when you
render a 3D scene with the camera tracking an object. The point you are
tracking always appears stationary. Examples of this in FlightGear are the
helicopter view and the tower view. If the origin is
Alan King wrote:
The 'nose' is a bad choice for either the viewing center or the FDM
center.
Except for the obvious fact that it's 100% unambiguous. It's not
uncommon for the FDM definition and 3D model to be done by different
authors. Take 21 people and ask them to identify the POS (or
On Saturday 10 January 2004 15:47, Andy Ross wrote:
Alan King wrote:
The 'nose' is a bad choice for either the viewing center or the FDM
center.
Except for the obvious fact that it's 100% unambiguous. It's not
uncommon for the FDM definition and 3D model to be done by different
authors.
On Saturday 10 January 2004 16:08, Andy Ross wrote:
Lee Elliott wrote:
The tip of the nose is fine with me but we need to clarify whether
the tip includes any nose-mounted pitots or probes.
Sure. Obviously it doesn't *really* matter. But picking some
unambiguous, obvious point on the
On Saturday, 10 January 2004 17:47, Andy Ross wrote:
Having the FDM coordinates and model coordinates match up is
critically important for collision issues like gear compression.
That is exactly my concern which made me ask about the FDM and model origins
in the first place.
I don't mind if
On Saturday 10 January 2004 16:34, Paul Surgeon wrote:
On Saturday, 10 January 2004 17:47, Andy Ross wrote:
Having the FDM coordinates and model coordinates match up is
critically important for collision issues like gear compression.
That is exactly my concern which made me ask about the
Paul wrote:
I don't mind if the origin of the FDM and model can be adjustable but once
they are set they MUST be static regardless of CG changes.
The Model Reference Point (MRP) must be static, yes. The CG will change,
but so will the vector from the CG to the MRP. It balances out. When the
On Sat, 10 Jan 2004 07:20:07 -0800,
Andy Ross [EMAIL PROTECTED] wrote in message
[EMAIL PROTECTED]:
Jon S. Berndt wrote:
The rigid body response to a force and torque can be in roll, pitch,
yaw, and/or X, Y, Z translation. That's six DoF. How does the
seventh degree come into play?
Andy Ross wrote:
Alan King wrote:
The 'nose' is a bad choice for either the viewing center or the FDM
center.
Except for the obvious fact that it's 100% unambiguous. It's not
uncommon for the FDM definition and 3D model to be done by different
authors. Take 21 people and ask them to identify
Lee Elliott wrote:
Definitely - I don't think I could accurately position a model to an
aerodynamic center.
LeeE
Then your model's relationship to how it flies is just as inaccurate. It
isn't by your or my or anyone else's vote or choice.
If the NOSE agrees in both, and you haven't
There is no choice in the matter. The center of the aircraft is the
center
of the aircraft and is the simplest point of agreement between the visual
and
the FDM, and simplest point of calculations for both. You can use the
nose as a
reference point, but you still better make very sure
On Sat, 2004-01-10 at 12:14, Alan King wrote:
Andy Ross wrote:
Alan King wrote:
The 'nose' is a bad choice for either the viewing center or the FDM
center.
Except for the obvious fact that it's 100% unambiguous. It's not
uncommon for the FDM definition and 3D model to be done
Jon Berndt wrote:
You are in an A-10 with a maverick on one side. You have an aircraft CG
(which the FDM is reporting the position of) and an MRP, which the FDM is
also supplying to FlightGear. The MRP is given to FlightGear in lat/lon/alt.
The FDM calculates that position because it knows where
Andy Ross wrote:
Lee Elliott wrote:
The tip of the nose is fine with me but we need to clarify whether
the tip includes any nose-mounted pitots or probes.
Sure. Obviously it doesn't *really* matter. But picking some
unambiguous, obvious point on the fuselage just seems much more sane
to me
It is hard to tell from what's said whether you're using the
COL as the
reference or the CG. COL is the real reference to use in the
FDM, the CG is
purposefully forward on most craft for stability. The CG swings
around the COL
pivot point noticably when you change pitch. Also all
Alan King [EMAIL PROTECTED] said:
Andy Ross wrote:
Alan King wrote:
The 'nose' is a bad choice for either the viewing center or the FDM
center.
Except for the obvious fact that it's 100% unambiguous. It's not
uncommon for the FDM definition and 3D model to be done by
Alan King [EMAIL PROTECTED] said:
The 'nose' is a bad choice for either the viewing center or the FDM center.
It wouldn't be an FDM center. It is only an easy to define reference point.
Everything works around the POS. The nose is just an arbitrary point how ever
many feet ahead.
Lee Elliott [EMAIL PROTECTED] said:
The tip of the nose is fine with me but we need to clarify whether the tip
includes any nose-mounted pitots or probes.
I'm specifically thinking about the TSR2 here, which has a nose mounted probe
but there will probably be others, if there aren't
Maybe a description of the nose location should be a standard
comment at the top of the FDM config files?
Yes, that is a very good idea. In fact, the last model I started to write
(B747) contained all the data the model was based on as well as source
references. The DAVE-ML standard being
On Behalf Of Alan King
Alan: Visit jsbsim.org, select the Links item, and look for the references
marked with a yellow checkbox square. Those references are the most
important and helpful ones.
Jon
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[EMAIL PROTECTED]
On Sat, 2004-01-10 at 14:10, Alan King wrote:
Jon Berndt wrote:
You are in an A-10 with a maverick on one side. You have an aircraft CG
(which the FDM is reporting the position of) and an MRP, which the FDM is
also supplying to FlightGear. The MRP is given to FlightGear in lat/lon/alt.
Jon Berndt wrote:
structural frame. The 3D modeler has no clue about (and probably doesn't
care to know about) where the CG is - and that's fine. The FDM and the 3D
model, though, *do* need to agree on a common MRP (Model Reference Point)
that the FDM can supply to the FlightGear scene code for
I see what you're doing now. You are letting them just use
the nose, and
then shifting the FDM nose point until the FDM center is near the
visual center.
Not really. The FDM still calculates the position of the CG of the aircraft.
It's just that we know exactly where the agreed-upon MRP
Jim Wilson wrote:
Maybe this will help: Unless you crash the plane, or you are flying a
concored sst, the nose will _always_ have exactly the same relationship in 3D
space to the furthest aft point of it's tail. The x, y, z distances between
the two points will always always be the same no
Tony Peden wrote:
Once the wheels are off the ground, the center of gravity is the point
about which the aircraft rotates. It does not rotate around the aero
center or any other point.
Yes, been a while since I'd used the POS. It is the other way around, with a
fixed POS it's the best point
Jon Berndt wrote:
I see what you're doing now. You are letting them just use
the nose, and
then shifting the FDM nose point until the FDM center is near the
visual center.
Not really. The FDM still calculates the position of the CG of the aircraft.
It's just that we know exactly where the
I said the other day and I will say it now the FDM does NOT require
a 3D model.
Have a look at the attachment this is the 747 flying sideways,quite happily,
as a 737.If the 3D model affected the FDM then this should not fly.
The 3D model should have its MRP as close to the CofG as you can get, if
Alan King writes
You do a 20 foot long plane FDM, with CG at 10 feet. I draw a
3000 foot long plane. The noses match. Does about 2980 feet of my plane
sink into the ground? What makes sure that the CG is put at the right
place in the visual model with the nose as the only reference?
On Saturday 10 January 2004 20:17, Alan King wrote:
Lee Elliott wrote:
Definitely - I don't think I could accurately position a model to an
aerodynamic center.
LeeE
Then your model's relationship to how it flies is just as inaccurate.
It isn't by your or my or anyone else's vote or
Jon Berndt writes
Have a look at the attachment this is the 747 flying sideways,quite
happily,
as a 737.If the 3D model affected the FDM then this should not fly.
Nobody is saying the 3D model affects the FDM - that's not the point.
Reading some of the replys it seem to me that it does
The
On Sat, 2004-01-10 at 19:20, Alan King wrote:
Jon Berndt wrote:
I see what you're doing now. You are letting them just use
the nose, and
then shifting the FDM nose point until the FDM center is near the
visual center.
Not really. The FDM still calculates the position of the CG
On Sat, 2004-01-10 at 18:31, Alan King wrote:
Tony Peden wrote:
Once the wheels are off the ground, the center of gravity is the point
about which the aircraft rotates. It does not rotate around the aero
center or any other point.
Yes, been a while since I'd used the POS. It is
On Saturday 10 January 2004 21:57, Jim Wilson wrote:
Lee Elliott [EMAIL PROTECTED] said:
The tip of the nose is fine with me but we need to clarify whether the
tip includes any nose-mounted pitots or probes.
I'm specifically thinking about the TSR2 here, which has a nose mounted
probe
Including prop cones sounds fine. I'm not sure about the three inch limit
though - one of the later B-52 experimental a/c had a long probe attached
to
it, that looked thicker than 3 but I'd be inclined not to use that as the
reference point, but use the nose location on a standard a/c.
How
Jon S Berndt writes
Paul Surgeon wrote:
Shucks ... I must be tired or something because this is getting more and
more confusing by the minute.
What is this arbitrary point you are referring to?
It is a location which you can choose. You can use the CG, the nose of the
aircraft, the center
On Thursday, 8 January 2004 23:34, Jon S Berndt wrote:
Paul:
We (FDM) simply report the location of the
reference point (I think we agreed it would be the forward-most
position of the aircraft, like the prop hub tip, or nose tip) and
FlightGear places the reference point (tip of nose, for
On Friday, 9 January 2004 16:41, Innis Cunningham wrote:
Exactly.
At the risk of putting my foot squarely in my mouth the FDM does not
care what the model looks like or where it is.The reference point for the
model is usually put somewhere close to the centre of the model so the
model will
On Fri, 9 Jan 2004 23:58:35 +0200
Paul Surgeon [EMAIL PROTECTED] wrote:
On Thursday, 8 January 2004 23:34, Jon S Berndt wrote:
Paul:
We (FDM) simply report the location of the
reference point (I think we agreed it would be the forward-most
position of the aircraft, like the prop hub tip, or nose
Paul Surgeon wrote:
Aha!
So AC_AERORP = (0,0,0) in FlightGear's 3D aircraft model space?
No, sorry. AC_EARORP is the published offset from CG to where the forces
act. For the F-16 that would be 35% chord (and CG is 25% chord).
Maybe it's good to know that I had lots of troubles understanding
On Saturday, 10 January 2004 00:35, Erik Hofman wrote:
No, sorry. AC_EARORP is the published offset from CG to where the forces
act. For the F-16 that would be 35% chord (and CG is 25% chord).
How do I go about calculating where the forces act?
Is this data supposed to be published or can I
Erik Hofman wrote:
Paul Surgeon wrote:
Aha!
So AC_AERORP = (0,0,0) in FlightGear's 3D aircraft model space?
No, sorry. AC_EARORP is the published offset from CG to where the
forces act. For the F-16 that would be 35% chord (and CG is 25%
chord).
Surely that's an approximation, no? A
On Saturday, 10 January 2004 00:35, Erik Hofman wrote:
No, sorry. AC_EARORP is the published offset from CG to where the forces
act. For the F-16 that would be 35% chord (and CG is 25% chord).
Just *maybe* I got it this time around. :)
So any distance in the FDM is just an offset from
Paul Surgeon [EMAIL PROTECTED] said:
On Saturday, 10 January 2004 00:35, Erik Hofman wrote:
No, sorry. AC_EARORP is the published offset from CG to where the forces
act. For the F-16 that would be 35% chord (and CG is 25% chord).
Just *maybe* I got it this time around. :)
So any
Paul:
The root of the problem - though it is not really a problem - is that the
FDM cares about modeling where the aircraft is in the world based on the
aircraft CG, and the 3D model wants to be in the correct spot in the world,
too, but how does one decide where to place it? Can one simply take
On Fri, 2004-01-09 at 17:29, Paul Surgeon wrote:
On Saturday, 10 January 2004 00:35, Erik Hofman wrote:
No, sorry. AC_EARORP is the published offset from CG to where the forces
act. For the F-16 that would be 35% chord (and CG is 25% chord).
Just *maybe* I got it this time around. :)
Is position 0,0,0 of an aircraft model the same point as 0,0,0 of the JSBSim
FDM in FlightGear?
I know the JSBSim FDM defines everything using the nose as the origin but I'm
trying to figure out if my model and the FDM are lined up correctly.
BTW: What is this I hear about plib snapping
Paul Surgeon wrote:
Is position 0,0,0 of an aircraft model the same point as 0,0,0 of the JSBSim
FDM in FlightGear?
I know the JSBSim FDM defines everything using the nose as the origin but I'm
trying to figure out if my model and the FDM are lined up correctly.
No JSBSim does not.
JSBSim uses
On Thursday, 8 January 2004 21:03, Erik Hofman wrote:
Paul Surgeon wrote:
Is position 0,0,0 of an aircraft model the same point as 0,0,0 of the
JSBSim FDM in FlightGear?
I know the JSBSim FDM defines everything using the nose as the origin but
I'm trying to figure out if my model and
Paul Surgeon wrote:
On Thursday, 8 January 2004 21:03, Erik Hofman wrote:
Paul Surgeon wrote:
Is position 0,0,0 of an aircraft model the same point as 0,0,0 of the
JSBSim FDM in FlightGear?
I know the JSBSim FDM defines everything using the nose as the origin but
I'm trying to figure out if my
On Thursday, 8 January 2004 21:54, Erik Hofman wrote:
Ehrm, I just discovered it is not very helpful what I said.
I should have said that the *3d models* origin (0, 0, 0) would be places
at the FDM models static CG. The CG of the FDM is (again) relative to
the arbitrary reference point (which
Paul Surgeon wrote:
Shucks ... I must be tired or something because this is getting more and more
confusing by the minute.
What is this arbitrary point you are referring to?
It is a location which you can choose. You can use the CG, the nose of
the aircraft, the center location of the front of
On Thu, 08 Jan 2004 21:34:44 +0100
Erik Hofman [EMAIL PROTECTED] wrote:
Paul Surgeon wrote:
Shucks ... I must be tired or something because this is getting more
and more confusing by the minute.
What is this arbitrary point you are referring to?
It is a location which you can choose. You can
Jon S Berndt [EMAIL PROTECTED] said:
Within the FDM our math model really doesn't care about the specific
locations of anything. We really only care about the relative
distances from the aircraft CG of things like the wheels, the wings,
the aerodynamic reference point, the pilot eyepoint,
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