[x3d-public] candidate feature: display bounding box

Andreas Plesch andreasplesch at gmail.com
Sat Feb 1 16:41:19 PST 2020

short responses below:

---on the phone---

On Sat, Feb 1, 2020, 4:42 PM Don Brutzman <brutzman at nps.edu> wrote:

> Great point below regarding world coordinates that we forgot to mention
> during Friday's discussion Andreas.
> Responding to your points one by one:
> On 1/24/2020 9:16 AM, Andreas Plesch wrote:
> > Another aspect of showBBox is whether the displayed bbox should
> > replace or augment the normal rendering. Probably augmenting is what
> > most would assume but I think it would need to be spelled out.
> The prose below seemed unambiguous, please check.

ok, the prose is clear enough.

> > Another aspect is how to deal with non-visual content of a
> > X3DBoundedObject, say an empty Group with explicit bounding box, or a
> > Viewpoint or ProximitySensor inside a Transform with explicit bounding
> > box. Probably just display bbox if explicit, and ignore if no bounding
> > box can be computed. Does that need to be specified ?
> Inline is another good case similar to (perhaps temporarily) empty Group
> node.  Spec sayeth:
> * X3D Architecture, 10.2.2 Bounding boxes
> https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/group.html#BoundingBoxes
> "The bounding box shall be large enough at all times to enclose the union
> of the group's children's bounding boxes;"
> so we should be good on that score.  Note the "at all times" above which
> seems to apply that actual bounding box sizes always get displayed.

An empty group has an actual bbox size of 0. How could such a bbox be
displayed ? A point ?
Or by nothing ?

> > X3D defines the bounding box aligned with local coordinate system:
> >
> https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/group.html#BoundingBoxes
> > If the appearance of a display bounding box is left unspecified, then
> > it would make sense to also allow display as world axis aligned
> > bounding boxes.
> Added ", so that both are aligned with world coordinates" as follows:

If "both" is referring to bbox and associated geometry, then it is unclear
why aligning geometry is mentioned.

Aligning the bbox with world axes would mean that all displayed bboxes have
the same orientation which could be helpful. The drawback is that the
orientation of the geometry would be hidden.

> ======================================
> https://www.web3d.org/member-only/mantis/view.php?id=1277
> 10.3.1 X3DBoundedObject
>      SFBool [in out] displayBBox FALSE
> "When displayBBox is true, the bounding box is displayed for the
> associated geometry, so that both are aligned with world coordinates. The
> bounding box is displayed regardless of whether contained content is
> visible."
> ======================================
> > Finally, I think any more sophisticated bounding box rendering would
> > need to be left to an author, using switch nodes, or the visible
> > field, or prototypes. For example, an author could just place a shape
> > representing a bounding box (eg. a transparent box, or glowing cage
> > with the right dimensions) as a sibling to the bounded object and
> > control its display. If there are many objects, these are typically
> > generated, and the generation then can also generate the bounding box
> > shapes.
> agreed in principle during prior corresponding group discussion, this
> keeps spec terse and gives implementers freedom to "do the right thing" on
> their own.

> all the best, Don
> --
> Don Brutzman  Naval Postgraduate School, Code USW/Br
> brutzman at nps.edu
> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA   +1.831.656.2149
> X3D graphics, virtual worlds, navy robotics
> http://faculty.nps.edu/brutzman
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