plib-users

Re: [Plib-users] Selecting with mouse

[Steve B. <sjb...@ai...>]

Curtis L. Olson wrote:

> I think step one would be to get a general purpose vector/scene-graph
> intersection routine in plib.  Plib does have something that will
> intersect a z=up vector with the geometry (for use in finding ground
> height in a z=up game.)  But, there needs to be a more general purpose
> routine that can find intersections with any arbitrary vector.

Whilst I agree that this is useful - for selection, it's better to use
the OpenGL mechanism because it allows you to select within a rubber-banded
region - and it stands a good chance of being hardware accellerated.

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net

Re: [Plib-users] Selecting with mouse

[Curtis L. O. <cu...@me...>]

David,

I think step one would be to get a general purpose vector/scene-graph
intersection routine in plib.  Plib does have something that will
intersect a z=up vector with the geometry (for use in finding ground
height in a z=up game.)  But, there needs to be a more general purpose
routine that can find intersections with any arbitrary vector.

FlightGear has something close, but it is highly optimized and
specialized for the flightgear scenery so it may not work as general
purpose drop in to plib.

But, once you have such a thing, the it should be relatively straight
forward to figure out which vector goes from your eye/camera view
point through the near clip plane at the mouse coordinates, and then
intersect this vector with the scene graph.

You'll likely need to do some post processing of the results to find
the particular intersection point of interest, but that would be
pretty application specific anyway.

Plib does have some sort of "LOS" intersection routine stubbed in, but
last time I checked in was completely in-op.

That's how my mind works any way, there's probably a much
cleverer/quicker way with inverting the camera matrix or something,
but I don't feel that matrix-friendly today to even try to think that
one through.

Regards,

Curt.


David Megginson writes:
> Norman Vine writes:
> 
>  > If the PPE source is that 'opaque' then a 'refresher' course in 
>  > the OpenGL 'way' might help
>  > http://fly.cc.fer.hr/~unreal/theredbook/chapter12.html
> 
> That's not the issue -- I understand (most of) the OpenGL stuff, but I
> find the PPE source very difficult to follow.  No offence is intended
> to the authors; my point is just that "read PPE" isn't particularly
> helpful advice either to me or to the others who've posted the same
> question.
> 
> I'd like to make two major points:
> 
> 1. The lack of a simple objects-under-the-mouse function in SSG is a
>    serious gap; i.e. it's a need-to-have, not a want-to-have feature
>    for a general-purpose scene-graph API.
> 
> 2. I'm not assuming that it's Steve's responsibility to fill that gap,
>    but would be grateful for more concrete guidance from the plib
>    development community as a whole.
> 
> Point #1 might not be self-evident to someone like Steve who writes
> high-end simulation software that will be used with prebuilt panels
> and cockpits, but it's critical for the PC world.  It's useful not
> only for operating instruments in a flight or racing simulator, but
> also for manipulating objects in a modeller, identifying features in a
> 3D GIS display, etc. etc. etc.  There's no point making each
> application writer recreate this code from scratch.
> 
> 
> All the best,
> 
> 
> David
> 
> -- 
> David Megginson, da...@me..., http://www.megginson.com/
> 
> 
> -------------------------------------------------------
> This sf.net email is sponsored by:ThinkGeek
> Welcome to geek heaven.
> http://thinkgeek.com/sf
> _______________________________________________
> plib-users mailing list
> pli...@li...
> https://lists.sourceforge.net/lists/listinfo/plib-users

-- 
Curtis Olson   IVLab / HumanFIRST Program       FlightGear Project
Twin Cities    cu...@me...                  cu...@fl...
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org

Re: [Plib-users] Selecting with mouse

[David M. <da...@me...>]

Norman Vine writes:

 > If the PPE source is that 'opaque' then a 'refresher' course in 
 > the OpenGL 'way' might help
 > http://fly.cc.fer.hr/~unreal/theredbook/chapter12.html

That's not the issue -- I understand (most of) the OpenGL stuff, but I
find the PPE source very difficult to follow.  No offence is intended
to the authors; my point is just that "read PPE" isn't particularly
helpful advice either to me or to the others who've posted the same
question.

I'd like to make two major points:

1. The lack of a simple objects-under-the-mouse function in SSG is a
   serious gap; i.e. it's a need-to-have, not a want-to-have feature
   for a general-purpose scene-graph API.

2. I'm not assuming that it's Steve's responsibility to fill that gap,
   but would be grateful for more concrete guidance from the plib
   development community as a whole.

Point #1 might not be self-evident to someone like Steve who writes
high-end simulation software that will be used with prebuilt panels
and cockpits, but it's critical for the PC world.  It's useful not
only for operating instruments in a flight or racing simulator, but
also for manipulating objects in a modeller, identifying features in a
3D GIS display, etc. etc. etc.  There's no point making each
application writer recreate this code from scratch.


All the best,


David

-- 
David Megginson, da...@me..., http://www.megginson.com/

Re: [Plib-users] Selecting with mouse

[Norman V. <nh...@ca...>]

David Megginson

> Steve Baker writes:
> 
>  > PLIB wasn't ever designed to do this - so it's not a simple
>  > mechanism and it's not documented - if you want to do it, you'll
>  > *HAVE* to read the PPE sources.
>  > 
>  > I'm sorry if that's not convenient - but like I said, PLIB wasn't
>  > designed with this kind of thing in mind.
> 
> It's not a matter of convenience -- after two hours with the PPE
> sources, I was scarcely any more enlightened than I am now.

Hmm..  

If the PPE source is that 'opaque' then a 'refresher' course in 
the OpenGL 'way' might help
http://fly.cc.fer.hr/~unreal/theredbook/chapter12.html

Norman

Re: [Plib-users] Old OpenFlight format

[Steve B. <sjb...@ai...>]

Chris wrote:

> I'd like to be able to read old OpenFlight (OF) format files. I think 
> some trouble I'm having with some OF files now is that they are the old 
> format, possibly. There was an old link to the code that would read the 
> old OF files in the FAQ that I think is now broken.

OpenFlight has gone through at least 14 versions - each incompatible
with all that preceded it.  Writing one loader that works with all of
them is REALLY painful.

(I *DEEPLY* loath OpenFlight - which isn't 'Open' by the way).

> What's a good way to determine if an OF file is the old or new format?

There is a version number somewhere at the top of the file.

> Where is the code that would handle the old OF format? Does the code it 
> still exist?

I don't recall whether we ever had a loader for older FLT versions.

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net

[Plib-users] Old OpenFlight format

[Chris <cc...@co...>]

Hi,

I'd like to be able to read old OpenFlight (OF) format files. I think 
some trouble I'm having with some OF files now is that they are the old 
format, possibly. There was an old link to the code that would read the 
old OF files in the FAQ that I think is now broken.

What's a good way to determine if an OF file is the old or new format?

Where is the code that would handle the old OF format? Does the code it 
still exist?

Thanks,

Chris A.
Virginia Beach, VA

Re: [Plib-users] Selecting with mouse

[David M. <da...@me...>]

Steve Baker writes:

 > PLIB wasn't ever designed to do this - so it's not a simple
 > mechanism and it's not documented - if you want to do it, you'll
 > *HAVE* to read the PPE sources.
 > 
 > I'm sorry if that's not convenient - but like I said, PLIB wasn't
 > designed with this kind of thing in mind.

It's not a matter of convenience -- after two hours with the PPE
sources, I was scarcely any more enlightened than I am now.

We've already begun this discussion, but it's worth repeating that
this should be core functionality for a scene-graph API -- any 3D
editor or any game or simulation that allows the user to interact with
the scene graph using the mouse (i.e. to manipulate objects) will need
to do this.

If someone can explain what I need to do, I'll be happy to contribute
an ssgSelect() function so that we won't have to rehash this thread in
the future:

  ssgEntity ** ssgSelect (ssgRoot * root, ssgContext * context,
                          int mouse_x, int mouse_y);

(or something similar.)


All the best,


David

-- 
David Megginson, da...@me..., http://www.megginson.com/

Re: [Plib-users] Selecting with mouse

[Steve B. <sjb...@ai...>]

David Megginson wrote:
> Steve Baker writes:
> 
>  > > Does somebody have a good advice?
>  > 
>  > Take a good, long look at http://ppe.sf.net
>  > 
>  > Nobody is working on that project right now   :-(
>  > ...but it does allow you to pick polygons and vertices
>  > out of a ssgLeaf node and to edit it.
> 
> I found the ppe source complex and unhelpful, so I'll recommend
> against looking at it if you're already confused.

Well, it is complex but...

> Steve and others have assured me that it's easy to pick the SSG
> entities under a screen location with existing SSG code.

I don't think I ever said it was easy.  It's possible though.

PLIB wasn't ever designed to do this - so it's not a simple
mechanism and it's not documented - if you want to do it, you'll
*HAVE* to read the PPE sources.

I'm sorry if that's not convenient - but like I said, PLIB wasn't
designed with this kind of thing in mind.

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net

Re: [Plib-users] Selecting with mouse

[David M. <da...@me...>]

Steve Baker writes:

 > > Does somebody have a good advice?
 > 
 > Take a good, long look at http://ppe.sf.net
 > 
 > Nobody is working on that project right now   :-(
 > ...but it does allow you to pick polygons and vertices
 > out of a ssgLeaf node and to edit it.

I found the ppe source complex and unhelpful, so I'll recommend
against looking at it if you're already confused.

Steve and others have assured me that it's easy to pick the SSG
entities under a screen location with existing SSG code.  Could
someone please explain precisely how?  Let's assume that I have

  ssgRoot * root;

and

  ssgContext * context;

Using PUI, I receive a mouse click at x=30, y=50.  Now, exactly what
C++ code would I use to get the list of ssgEntity objects under that
screen location?


Thanks, and all the best,


David

-- 
David Megginson, da...@me..., http://www.megginson.com/

Re: [Plib-users] Selecting with mouse

[Steve B. <sjb...@ai...>]

SilvioCVdeAlmeida wrote:
> 
> I'm new to the list, so please excuse me if selection
> is an old issue here...
> 
> I'm working on a drawing system and I want to find the
> nice way to select an ssgLeaf with the mouse, in order
> to edit a colour for example.
> 
> My difficult is to isolate, from scenery, a traversal
> suitable to go inside a selecting function along with
> GL_SELECT, InitNames...
> 
> But SSG's by-element GL state management apparently
> make it difficult to treat some very OpenGL specific
> problems.
> 
> Does somebody have a good advice?

Take a good, long look at http://ppe.sf.net

Nobody is working on that project right now   :-(
...but it does allow you to pick polygons and vertices
out of a ssgLeaf node and to edit it.

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net

[Plib-users] Selecting with mouse

[SilvioCVdeAlmeida <scv...@gr...>]

Hello...

I'm new to the list, so please excuse me if selection
is an old issue here...

I'm working on a drawing system and I want to find the
nice way to select an ssgLeaf with the mouse, in order
to edit a colour for example.

My difficult is to isolate, from scenery, a traversal
suitable to go inside a selecting function along with
GL_SELECT, InitNames...

But SSG's by-element GL state management apparently
make it difficult to treat some very OpenGL specific
problems.

Does somebody have a good advice?

__________________________________________________________
SilvioCVdeAlmeida 2002.09.27
scv...@gr...

Re: [Plib-users] The examples

[Sebastian U. <ud...@ha...>]

On Wed, 11 Sep 2002, sjb...@ai... (Steve Baker) wrote:
> Date: Wed, 11 Sep 2002 18:36:00 -0500
> To: pli...@li...
> From: sjb...@ai... (Steve Baker)
> Reply-To: pli...@li...
> Subject: Re: [Plib-users] The examples
>
> Sebastian Ude wrote:
>
> > Again - argh ! From the automake manual:
>
> Well, on the theory of "Go With What Works" - and "Don't F**k With What
> You Don't Understand"...perhaps you'd be so kind as to put the
> Makefile.am's back to where they work - then I'll do another quick
> Examples/Demo's release.
>
> We can figure out what's really wrong later - but it's important that
> everyone can download working examples/demos.
>
> Thanks!

I am sorry Steve, but you can't blame the missing configure helper scripts
on me, and what you suggest does NOT solve the problem.

Look - mkinstalldirs, config.sub, config.guess and install.sh are not
listed the top-level Makefile.am; and not because I removed them, but
because they have never been in there (check the CVS archive, if you want)
!

So how did the files make into the plib-1.6.0.tar.gz tarball, then ? The
answer is simple: Because autoconf has always _automatically_ added these
files to the distribution. I verified it, it really does.

If the files were not added to the distribution, the reason for that was
that they were not in the directory prior to the 'make dist' ! In this
case, it does not help AT ALL to (re-)add anything to Makefile.am; the
build system just can't add a non-existing file to the distribution.


The question we need to ask is why the files were missing in the "examples"
directory, and the answer is that autoconf does NOT install the
'mkinstalldirs', 'missing', 'install-sh', 'config.sub', 'config.guess' in
the current directory if it finds them in '..'.

Try it - take a fresh PLIB CVS tree, run ./autogen.sh from the top-level
plib directory. autoconf will install the configure helper scripts to the
top-level plib dir.

Now, cd to 'examples' and run ./autogen.sh from there as well. autoconf
finds the helper scripts in '..' and does NOT install them to the
'examples' directory again.


As you see, everything works as long as you keep the directory hirarchie -
but if you distribute the 'examples' directory seperately, the example's
configure script won't find its helper scripts in '..' as it expected ->
BUMMER !

That's just the behaviour of autoconf. As you can see, the problem has
*nothing* to do with me removing the helper scripts from the examples
Makefile.am file, which I think was a good move by the way, because it is
just unnecessary to list them there.

Again - re-adding them would not help a single bit, because the problem is
not that the build system does not know about the scripts, but that the
build-system can't add non-existing files to the distribution.


Perhaps you'd be so kind as to do a bit of research in the future prior to
blaming me for problems that I am not responsible for.

Thanks.


The solution of the problem is - if it is not obvious - either to remove
the scripts from the top-level plib directory prior to excecuting
'autogen.sh' from the examples directory in order to make the distribution,
or to move the 'examples' dir out of the plib source tree. In both cases,
'autoconf' won't find the helper scripts in '..', which is what we want to
achieve.


- Sebastian

Re: [Plib-users] The examples

[Steve B. <sjb...@ai...>]

Sebastian Ude wrote:

> Again - argh ! From the automake manual:

Well, on the theory of "Go With What Works" - and "Don't F**k With What
You Don't Understand"...perhaps you'd be so kind as to put the Makefile.am's
back to where they work - then I'll do another quick Examples/Demo's release.

We can figure out what's really wrong later - but it's important that everyone
can download working examples/demos.

Thanks!

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net

Re: [Plib-users] The examples

[Sebastian U. <ud...@ha...>]

On Tue, 10 Sep 2002, sjb...@ai... (Steve Baker) wrote:
> Date: Tue, 10 Sep 2002 20:39:01 -0500
> To: pli...@li...
> From: sjb...@ai... (Steve Baker)
> Reply-To: pli...@li...
> Subject: Re: [Plib-users] The examples

[...]

> So, I use 'make dist' to make the distribution tarball - and it *used* to
> work.  Something must have happened to 'Makefile.am's "extra-dist" entry.
>
> Ah - yes - checking the CVS records, I see that *SOMEONE* has removed the
> entry requiring those files.
>
> That happened between version 1.5 and 1.6 of examples/Makefile.am ...and
> that entry was committed by....
>
>      Revision 1.6, Wed May 8 21:24:24 2002 UTC (4 months ago) by ude
>
> Hmmmm - someone by the name of "ude" ??

Again - argh ! From the automake manual:


What Goes in a Distribution
***************************

[...]

   For the most part, the files to distribute are automatically found by
Automake: all source files are automatically included in a distribution, as
are all `Makefile.am's and `Makefile.in's.  Automake also has a built-in
list of commonly used files which, if present in the current directory, are
automatically included.  This list is printed by `automake --help'.  Also,
files which are read by `configure' (i.e. the source files corresponding to
the files specified in the `AC_OUTPUT' invocation) are automatically
distributed.


~$ automake --version
automake (GNU automake) 1.4-p2

Copyright (C) 1999, 2001 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Written by Tom Tromey <tr...@cy...>
~$ automake --help
Usage: automake [OPTION] ... [Makefile]...

Generate Makefile.in for autoconf from Makefile.am

[...]

Files which are automatically distributed, if found:
  ABOUT-GNU           README              config.h.bot        ltcf-cxx.sh
  ABOUT-NLS           THANKS              config.h.top        ltcf-gcj.sh
  AUTHORS             TODO                config.sub          ltconfig
  BACKLOG             acconfig.h          configure           ltmain.sh
  COPYING             acinclude.m4        configure.in        mdate-sh
  COPYING.LIB         aclocal.m4          elisp-comp          missing
  ChangeLog           ansi2knr.1          install-sh          mkinstalldirs
  INSTALL             ansi2knr.c          libversion.in       stamp-h.in
  NEWS                config.guess        ltcf-c.sh           stamp-vti
  README              config.h.bot

Report bugs to <bug...@gn...>.


install-sh, mkinstalldirs, config.guess and config.sub are listed there.
What is going on ?


- Sebastian

Re: [Plib-users] Problem with rotations results

[Curtis L. O. <cu...@me...>]

David Megginson writes:
> Christian Mayer writes:
> 
>  > > Is this based on magnetic heading or true heading?
>  > 
>  > Doesn't matter for the question (as long as you are allways refering to
>  > the same type of heading). It only changes the absolute position of the
>  > tent.
> 
> Sure it does.  You might find a polar bear at the magnetic pole, but I
> don't know if it's as likely at the true pole.

Right, unless one of them is working for Santa, but in that case he
wouldn't be mean and nasty and wouldn't be chasing defensless hunters
around.

Curt.
-- 
Curtis Olson   IVLab / HumanFIRST Program       FlightGear Project
Twin Cities    cu...@me...                  cu...@fl...
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org

Re: [Plib-users] Problem with rotations results

[Norman V. <nh...@ca...>]

Steve Baker writes:

> Norman Vine wrote:
> 
> > Going back to my original question:
> > "When EXACTLY at the North Pole how may directions can you move"
> > 
> > Answer:
> > Only one, the only direction from the North Pole is SOUTH
> 
> Yep - if you are a zero-sized person.  

Almost  :-)  < see sig > 

> Otherwise, you get the
> interesting experience of your nose heading south at the same instant
> as your backside heading north and one arm going east while the other
> goes west...although after you've taken just one step, everything
> is more or less sorted out and heading more or less South!

Yep, and you have just 'nicely' described why the 'kludge' of offseting 
the pole position a 'smidge' works :-)

how-small-is-epsilon-anyway'ly yr's

Norman

Re: [Plib-users] Problem with rotations results

[Ben W. <be...@ec...>]

On September 11, 2002 08:19 am, Norman Vine wrote:
> Ben Woodhead writes:
> >Steve Baker writes
> >
> > > But anyway - this *is* classic 'Gymbal Lock'.
> >
> > Ah, I always thought gymbal lock was only when rotating around all 3 =
axes
>
> at
>
> > the same time.
> >
> > > As Norman suggested, you can visualise it in these
> > > terms:
> > >
> > >      "A hunter walks South one mile from his tent, then
> > >       he is chased due East for one mile by a ferocious Bear.
> > >       Having escaped, he walks North for one mile and finds
> > >       himself back at his tent.  What colour was the Bear?"
> > >
> > >      (White!)
> >
> > What? I don't get it..
>
> Going back to my original question:
> "When EXACTLY at the North Pole how may directions can you move"
>
> Answer:
> Only one, the only direction from the North Pole is SOUTH
>
> Norman
>
Hahaha, thats good, I like that.. I just want to let you all know that yo=
u=20
guys are crazy.. joking.. :)

Ben
>
>
>
> -------------------------------------------------------
> In remembrance
> www.osdn.com/911/
> _______________________________________________
> plib-users mailing list
> pli...@li...
> https://lists.sourceforge.net/lists/listinfo/plib-users

Re: [Plib-users] Problem with rotations results

[Steve B. <sjb...@ai...>]

Norman Vine wrote:

> Going back to my original question:
> "When EXACTLY at the North Pole how may directions can you move"
> 
> Answer:
> Only one, the only direction from the North Pole is SOUTH

Yep - if you are a zero-sized person.  Otherwise, you get the
interesting experience of your nose heading south at the same instant
as your backside heading north and one arm going east while the other
goes west...although after you've taken just one step, everything
is more or less sorted out and heading more or less South!

----------------------------- Steve Baker -------------------------------
Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
URLs : http://www.sjbaker.org
        http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
        http://prettypoly.sf.net http://freeglut.sf.net
        http://toobular.sf.net   http://lodestone.sf.net

Re: [Plib-users] Problem with rotations results

[David M. <da...@me...>]

Christian Mayer writes:

 > > Is this based on magnetic heading or true heading?
 > 
 > Doesn't matter for the question (as long as you are allways refering to
 > the same type of heading). It only changes the absolute position of the
 > tent.

Sure it does.  You might find a polar bear at the magnetic pole, but I
don't know if it's as likely at the true pole.


All the best,


David

-- 
David Megginson, da...@me..., http://www.megginson.com/

Re: [Plib-users] Problem with rotations results

[Norman V. <nh...@ca...>]

Ben Woodhead writes:
>Steve Baker writes

> > But anyway - this *is* classic 'Gymbal Lock'.
>
> Ah, I always thought gymbal lock was only when rotating around all 3 axes
at
> the same time.
>
> > As Norman suggested, you can visualise it in these
> > terms:
> >
> >      "A hunter walks South one mile from his tent, then
> >       he is chased due East for one mile by a ferocious Bear.
> >       Having escaped, he walks North for one mile and finds
> >       himself back at his tent.  What colour was the Bear?"
> >
> >      (White!)
>
> What? I don't get it..

Going back to my original question:
"When EXACTLY at the North Pole how may directions can you move"

Answer:
Only one, the only direction from the North Pole is SOUTH

Norman

Re: [Plib-users] Problem with rotations results

[Christian M. <ma...@Ch...>]

"Curtis L. Olson" wrote:
> 
> Steve Baker writes:
> >      "A hunter walks South one mile from his tent, then
> >       he is chased due East for one mile by a ferocious Bear.
> >       Having escaped, he walks North for one mile and finds
> >       himself back at his tent.  What colour was the Bear?"
> 
> Is this based on magnetic heading or true heading?

Doesn't matter for the question (as long as you are allways refering to
the same type of heading). It only changes the absolute position of the
tent.

But as everybody around here wants a house/flat with a south side front
I should build a house on the same spot where the tent was. Then I can
get rich as all sides re facing south!

CU,
Christian

--
The idea is to die young as late as possible.        -- Ashley Montague

Re: [Plib-users] Problem with rotations results

[Ben W. <za...@ec...>]

----- Original Message -----
From: "Steve Baker" <sjb...@ai...>
To: <pli...@li...>
Sent: Tuesday, September 10, 2002 11:46 PM
Subject: Re: [Plib-users] Problem with rotations results


> Ben Woodhead wrote:
>
> > Wow, I had no idea the results returning from a matrix were that like
that.. I
> > understood what you meant, when you said h <> h, and so on. But I didn't
> > realise just how off they would actually be.
>
> Yes - well, it's a mathematical fact.  There are an infinite number of
ways
> to represent an arbitary rotation matrix in terms of Euler angles - and
the
> code has no way to know which one you wanted - so it just picks one.
>
> It's hard to know what else we could do.
>
> > Anyway back to the point, I was
> > wrong about the 0 and 180, its at 90 degrees that cause the problem.
Here is
> > the header, pitch and role from the 3 different rotations. Take a close
look
> > at the pitch.
>
> (BTW: The word is "Roll" - not "Role" and "Heading" - not "Header")
>
> > Pitch
> > Header: -0.000000, Pitch: 88.002075, Role: -0.000000
> > Header: -0.000000, Pitch: 89.004166, Role: -0.000000
> > Header: 0.000000, Pitch: 90.000000, Role: 90.000000
>
> Eh?  Are you sure the heading was zero?  I'd expect it to
> be -90 or something.

No, that was actually the log from the program running, that I copied into
here.. That was what was causing me the greef.

> But anyway - this *is* classic 'Gymbal Lock'.

Ah, I always thought gymbal lock was only when rotating around all 3 axes at
the same time.

> As Norman suggested, you can visualise it in these
> terms:
>
>      "A hunter walks South one mile from his tent, then
>       he is chased due East for one mile by a ferocious Bear.
>       Having escaped, he walks North for one mile and finds
>       himself back at his tent.  What colour was the Bear?"
>
>      (White!)

What? I don't get it..

> > As you can see in pitch when it hits 90 on pitch, role also goes to 90.
The
> > one thing that I just noticed is that non of the other rotations get to
> > exactly 90.0.
>
> It's not so much that Roll or Pitch is special, it actually comes
> about that way because of the order of rotational operations.
>
> The bottom line is that Mat-to-Coord is working OK - it's just
> that you have to understand it's limitations.

Well, thanks everybody.. I rewrote all the code to have not use coord and
everything is good..
Thanks Ben

> ----------------------------- Steve Baker -------------------------------
> Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
> URLs : http://www.sjbaker.org
>         http://plib.sf.net http://tuxaqfh.sf.net http://tuxkart.sf.net
>         http://prettypoly.sf.net http://freeglut.sf.net
>         http://toobular.sf.net   http://lodestone.sf.net
>
>
>
>
>
> -------------------------------------------------------
> In remembrance
> www.osdn.com/911/
> _______________________________________________
> plib-users mailing list
> pli...@li...
> https://lists.sourceforge.net/lists/listinfo/plib-users
>

Re: [Plib-users] The examples

[Ramy S. <sa...@ic...>]

Wow you guys are fast. Thanks SO much for getting back to me so quick. I 
truly appreciate it. Yes, I am, in fact using RH 7.2 (I'm going to call 
it 7 point "poo" from now on). I will seek the new mesa package. Thanks 
a million!

-Ramy

ha...@sl... wrote:

>About the OpenGL Context, are you using Red Hat 7.2?  If so, I believe 
>they updated their Mesa package to fix this problem.
>
>--
>Brian
>
>
>On Tue, 10 Sep 2002, Ramy Sadek wrote:
>
>>Hi all. I hope I'm not stating a known or obvious problem.
>>
>>The examples don't work for me. If I try to get 1.6.1, configure 
>>complains about install-sh missing. If I run the compile by hand (which 
>>works) for, say, viewer, I get an error complaining that ssgInit is 
>>called without a valid OpenGL context. This seems bizarre since I 
>>haven't touched the code itself.
>>
>>Anyone have similar problems?
>>
>>-Ramy
>>
>>
>>
>>-------------------------------------------------------
>>In remembrance
>>www.osdn.com/911/
>>_______________________________________________
>>plib-users mailing list
>>pli...@li...
>>https://lists.sourceforge.net/lists/listinfo/plib-users
>>
>

Re: [Plib-users] Problem with rotations results

[Norman V. <nh...@ca...>]

Curtis L. Olson

> Steve Baker writes:
> >      "A hunter walks South one mile from his tent, then
> >       he is chased due East for one mile by a ferocious Bear.
> >       Having escaped, he walks North for one mile and finds
> >       himself back at his tent.  What colour was the Bear?"
> 
> Is this based on magnetic heading or true heading?
> 
> >      (White!)
> 
> Extra credit:  What colo[u]r were his pants.

Same colo[u]r as the Bear !

need-open-water-nearby-to-bath-in'ly yr's

Norman

Re: [Plib-users] Problem with rotations results

[Curtis L. O. <cu...@me...>]

Steve Baker writes:
>      "A hunter walks South one mile from his tent, then
>       he is chased due East for one mile by a ferocious Bear.
>       Having escaped, he walks North for one mile and finds
>       himself back at his tent.  What colour was the Bear?"

Is this based on magnetic heading or true heading?

>      (White!)

Extra credit:  What colo[u]r were his pants.

Curt.
-- 
Curtis Olson   IVLab / HumanFIRST Program       FlightGear Project
Twin Cities    cu...@me...                  cu...@fl...
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org