Rory Douglas wrote:
>
> Hi there
>
> >From this discussion I was just wondering, what does the method
> getImagePlateToVworld() in Canvas3D actually do?
> I realise it can't give you one of the co-ordinates,but which one? Does the
> transform returned correspond to the inverse of the matrix that takes
> Normalised Projection co-ords into screen space?
Hi Rory, here is an example (from 3D User Interfaces whith Java3D)
how to use getImagePlateToVworld():
Canvas3dD canvas;
int mouseX, mouseY;
Point3d rayOrg = new Point3d();
Vector3d rayDir = new Vector3d();
// Get eye position in view space
Point3d eyePos = new Point3d();
canvas.getCenterEyeInImageOlate(eyePos);
// Translate mouse canvas position to view space
Point3d mousePos = new Point3d();
canvas.getPixelLocationInImagePlate(mouseX, mouseY, mousePos);
//Get the view-to-world transform
Transform3D xform = new Transform3D();
canvas.getImagePlateToVworld(xform);
//transform eye and mouse from view to world space
xform.transform(eyePos);
xform.transform(mousePos);
//save the world pick ray origin
rayOrg.set(eyePos);
//build the world pick ray direction
rayDir.sub(mousePos, rayOrg);
rayDir.normalize()
//build pick ray
PickRay ray = new PickRay(rayOrg,rayDir);
//throw the pick ray into the scene at all leaf shape
// nodes under pick root (e.g. Branchgroup)
Scengraph paths[] = root.pickAllSorted(ray)
Now you use this to determine the hit point with objects in the scene,
which in fact will give you a point with 3 coordinates (x,y,z).
For 2 of these points it's easy to compute their distance.
Hope it helps
Joerg
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