Hiya Chris Allright, I dug into the maths and seem to have solved it. I'll share it here, as I feel it is useful.
QC file is attached this email.
To project a 3d point onto space, use this formula and z-axis scale factor:
var scaleFactor = 0.58;
screenX = obX * (1 / ( 1 + (-obZ * scaleFactor) ));
screenY = obY * (1 / ( 1 + (-obZ * scaleFactor) ));
---
I need it for a top layer of 2d overlays and pointers that do not scale, but
accurately follow a moving 3d scene.
All the best
Sune Watts
---
On Tue, Nov 3, 2009 at 1:34 PM, Chris Wood <[email protected]> wrote:
> If you really want to do it manually, you'll need to learn some maths.
> You need to calculate the distance of a point on a sphere from the
> camera (the camera position in QC is (0,0,-1) if I remember right) to
> determine size and perspective transform.
>
> I don't understand why you need to convert though - if you have the
> xyz position, why not just tell QC to draw your image at that xyz
> position?
>
> You could also use the 3D transform patch perhaps?
>
> Chris
>
>
> 2009/11/3 Sune Watts <[email protected]>:
> > Sorry if I was unclear:
> >
> > How to translate an (x, y, z) point into (x, y) screen coordinates --
> >
> > For example, you have a rotating globe and want to know the screen
> > coordinates of a certain city on the globe.
> >
> >
> > Best regards
> > Sune Watts
> >
> >
> > ---
> >
> >
> > On Tue, Nov 3, 2009 at 11:02 AM, Chris Wood <[email protected]> wrote:
> >>
> >> QC supports 3D space already. There's 2 ways to show a 2D image:
> >> Billboard (this is best for overlays and the like, and is 2D based)
> >> and Sprite (this is similar to billboard, but exists in full 3D space
> >> so you can move it on Z, and rotate on all 3 axis.
> >>
> >> Most likely, sprite will cover your needs.
> >>
> >> Chris
> >>
> >>
> >> 2009/11/3 Sune Watts <[email protected]>:
> >> > Hello all;
> >> >
> >> > I need to pin a 2D billboard onto a (moving) point in 3D space.
> >> >
> >> > I haven't been able to find any info on the z-axis scaling QC employs.
> >> >
> >> > Has anybody got a handle on mathematically converting a point in 3D
> >> > space to
> >> > 2D screen space?
> >> >
> >> >
> >> > All the best
> >> > -SW
> >> >
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> >> >
> >
> >
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3d_to_2d_coords.qtz
Description: Binary data
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