pyopengl-users

[PyOpenGL-Users] gluUnProject Projection Failed

[Eleftherios G. <gar...@gm...>]

Hello,

I am using the pyopengl version 3.0.0 in Ubuntu 9.10 and I am trying to get
a pick ray when I press 'p' in the keyboard. To do that I found that is well
suggested to use gluUnProject.

if key == 'p':


            modelviewmatrix=gl.glGetDoublev(gl.GL_MODELVIEW_MATRIX)

            print 'ModelViewMatrix'
            print modelviewmatrix

            projectionmatrix=gl.glGetDoublev(gl.GL_PROJECTION_MATRIX)
            print 'ProjectionMatrix'
            print projectionmatrix

            viewport=gl.glGetDoublev(gl.GL_VIEWPORT)

            print 'Viewport'
            print viewport

            print float(x), viewport[3]-float(y)

            wx,wy,wz= glu.gluUnProject(float(x),viewport[3]-float(y),0.,
                                              modelviewmatrix,
                                              projectionmatrix,
                                              viewport)

            print 'World Coordinate'
            print wx,wy,wz

And the output is giving me a value error projection failed as you can see
below
ModelViewMatrix
[[   1.    0.    0.    0.]
 [   0.    1.    0.    0.]
 [   0.    0.    1.    0.]
 [   0.    0. -150.    1.]]
ProjectionMatrix
[[ 1.28300059  0.          0.          0.        ]
 [ 0.          1.73205078  0.          0.        ]
 [ 0.          0.         -1.00010002 -1.        ]
 [ 0.          0.         -0.20001     0.        ]]
Viewport
[    0.     0.  1080.   800.]
693.0 489.0
Traceback (most recent call last):
  File "_ctypes/callbacks.c", line 295, in 'calling callback function'
  File "scene.py", line 294, in keystroke
    viewport)
  File "/usr/lib/pymodules/python2.6/OpenGL/lazywrapper.py", line 9, in
__call__
    return wrapper( baseFunction, *args, **named )
  File "/usr/lib/pymodules/python2.6/OpenGL/GLU/projection.py", line 60, in
gluUnProject
    raise ValueError( """Projection failed!""" )
ValueError: Projection failed!

Any ideas?

Best wishes,
Eleftherios

Re: [PyOpenGL-Users] gluUnProject Projection Failed

[Greg E. <gre...@ca...>]

Eleftherios Garyfallidis wrote:

>             wx,wy,wz= glu.gluUnProject(float(x),viewport[3]-float(y),0.,
>                                               modelviewmatrix,
>                                               projectionmatrix,
>                                               viewport)

I don't think that 0 is a valid value for the z coordinate
when you're unprojecting in a perspective projection.

Also, to get a ray, you need to know *two* points in the scene.
The way I do it is to call gluUnProject twice, once with
z = the near plane, and once with z = the far plane. A line
between the two resulting points gives you your pick ray.

-- 
Greg

Re: [PyOpenGL-Users] gluUnProject Projection Failed

[Eleftherios G. <gar...@gm...>]

Hello,

Thank you again for your response.

- Show quoted text -
On Tue, Apr 13, 2010 at 11:20 AM, Greg Ewing <gre...@ca...>wrote:

> Eleftherios Garyfallidis wrote:
> > to get
>
>> the near plane I believe you need to gluUnProject with z=0. and to get the
>> far plane you need to gluUnProject with z=1
>>
>
> You're quite right, I was misremembering, sorry.
>
>
>  Surprisingly, when I do glu.gluUnProject(x,viewport[3]-y,0.) and
>> glu.gluUnProject(x,viewport[3]-y,1.) in PyOpenGL it seems it works fine but
>> when I am feeding the transformation matrices by myself I am getting this
>> error "Projection Failed".
>>
>
> That sounds like there is something wrong with your matrices.
> How are you getting them? Are you getting them directly from
> OpenGL, or calculating them yourself? If you're calculating them
> yourself, you might be making a mistake somewhere.
>

> What happens if you retrieve the relevant matrices from OpenGL
> and feed them to gluUnProject? If that works, compare them with
> your own matrices to see if there is a difference.
>

  Yes this is what I am doing just calculating these matrices using the
following PyOpenGL functions

  import OpenGL.GL as gl

  modelviewmatrix=gl.glGetDoublev(gl.GL_MODELVIEW_MATRIX)

  projectionmatrix=gl.glGetDoublev(gl.GL_PROJECTION_MATRIX)

  viewport=gl.glGetDoublev(gl.GL_VIEWPORT)

  These matrices are numpy arrays do you think that it might be a problem
when we put these as input in gluUnProject? Should I transform them into
something else perhaps?

  By the way I do confirm that when using gluUnProject without feeding in
the transformation matrices as in glu.gluUnProject(x,viewport[3]
-y,0.) does work correctly :-) I made some tests with picking planes and the
accuracy of picking was excellent!!! The tests involved checking if the
segment AB (where A is near and B is far) intersects with planes. For my
application I need to check against many planes so I made a function for
this in cython. The link for the code is here

http://github.com/Garyfallidis/Fos/blob/master/fos/core/collision.pyx

Best wishes,
Eleftherios

Re: [PyOpenGL-Users] gluUnProject Projection Failed

[Gary H. <gh...@di...>]

Eleftherios Garyfallidis wrote:
> Hello,
>
> Thank you again for your response.
>
> - Show quoted text -
> On Tue, Apr 13, 2010 at 11:20 AM, Greg Ewing 
> <gre...@ca... <mailto:gre...@ca...>> wrote:
>
>     Eleftherios Garyfallidis wrote:
>     > to get
>
>         the near plane I believe you need to gluUnProject with z=0.
>         and to get the far plane you need to gluUnProject with z=1
>
>
>     You're quite right, I was misremembering, sorry.
>
>
>         Surprisingly, when I do glu.gluUnProject(x,viewport[3]-y,0.)
>         and glu.gluUnProject(x,viewport[3]-y,1.) in PyOpenGL it seems
>         it works fine but when I am feeding the transformation
>         matrices by myself I am getting this error "Projection Failed".
>
>
>     That sounds like there is something wrong with your matrices.
>     How are you getting them? Are you getting them directly from
>     OpenGL, or calculating them yourself? If you're calculating them
>     yourself, you might be making a mistake somewhere.
>
>
>     What happens if you retrieve the relevant matrices from OpenGL
>     and feed them to gluUnProject? If that works, compare them with
>     your own matrices to see if there is a difference.
>
>
>   Yes this is what I am doing just calculating these matrices using 
> the following PyOpenGL functions           
>
>   import OpenGL.GL as gl
>
>   modelviewmatrix=gl.glGetDoublev(gl.GL_MODELVIEW_MATRIX)
>
>   projectionmatrix=gl.glGetDoublev(gl.GL_PROJECTION_MATRIX)
>  
>   viewport=gl.glGetDoublev(gl.GL_VIEWPORT)


I have not followed this thread at all -- so I don't know the history.  
Nevertheless, I see a potential problem.

The call to gluUnProject expects the viewport to be passed in as 
integers (GLint*) so you should be using glGetIntegerv not glGetDoublev 
to get the viewport as an array of integers.

Here's gluUnProject's spec:
  GLint gluUnProject(    GLdouble winX,
       GLdouble winY,
       GLdouble winZ,
       const GLdouble * model,
       const GLdouble * proj,
       const GLint * view,           // !!!!!
       GLdouble* objX,
       GLdouble* objY,
      GLdouble* objZ);

Using glGetDoublev for the two matricies and glGetIntegerv for the 
viewport as input to gluUnProject has always worked well for me.

>
>   These matrices are numpy arrays do you think that it might be a 
> problem when we put these as input in gluUnProject? Should I transform 
> them into something else perhaps?
>
>   By the way I do confirm that when using gluUnProject without feeding 
> in the transformation matrices as in glu.gluUnProject(x,viewport[3]
> -y,0.) does work correctly :-) I made some tests with picking planes 
> and the accuracy of picking was excellent!!! The tests involved 
> checking if the segment AB (where A is near and B is far) intersects 
> with planes. For my application I need to check against many planes so 
> I made a function for this in cython. The link for the code is here
>
> http://github.com/Garyfallidis/Fos/blob/master/fos/core/collision.pyx
>
> Best wishes,
> Eleftherios
>  
>
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-- 
Gary Herron, PhD.
Department of Computer Science
DigiPen Institute of Technology
(425) 895-4418