Hi George,

Hmmm....I'm thinking, after all this, its not what I need anyhow, for the

third parameter to gluUnProject(). Sorry to give everyone the runaround. I

thought I needed an actual Z value. My problem must reside elsewhere -- and

I was surethis was it.

BTW, do you need this function yourself? I'll be glad to look t it and put

it into code for the group if anyone really needs it. -Ralph

> > > > I have a zNear value of 5.0, and a zFar value of 60.0.

> > > > When I click on an object in my scene, and call:

> > > > glReadPixels(x,y,1,1,GL_DEPTH_COMPONENT,GL_FLOAT,&selectedThingZ);

> > > > I get a value of 0.95 for my selectedThingZ.

> > > > What, actually, is that z value given my zNear and zFar (I have

loked at the

> > > > FAQ, but find nothing on this). Also, what would happen in

glOrthoMode?

> > > The redbook fig. 3-18 shows that depth coord values are in the

range of 0->1 and not linear.

Quote:> > > I'm no mathematician, if I'm not mistaken the z-buffer value is a

number representing the non-linear location in zNear-zFar

Quote:> > > space, so I would guess, that .95 squared of the z range + the znear

is the actual worldspace location, i.e.:

Quote:> > > znear+pow(.95,2)*(zfar-znear)

> > > 5 + .9025 *( 60 - 5 ) or 54.6375?

> > > pow may not be the precise way to convert the z value but it looks

about right.

> > The exact maths for doing this are described at the OpenGL SIGGRAPH

> > courses:

http://www.opengl.org/developers/code/sig99/advanced99/notes/node403....

Quote:> Like I said, I'm no mathematician.

> I can't get a resaonable value, can you/someone compute the example

provided?

> zin