[x3d-public] candidate feature: display bounding box

Don Brutzman brutzman at nps.edu
Sat Feb 1 17:57:38 PST 2020

On 2/1/2020 4:41 PM, Andreas Plesch wrote:
> short responses below:
> ---on the phone---
> On Sat, Feb 1, 2020, 4:42 PM Don Brutzman <brutzman at nps.edu <mailto: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 ?

An empty Group (or Inline or whatever) might still have positive bboxCenter and bboxSize values specified by the author, in the original scene, perhaps in anticipation of animation changes.

>      > 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.

The goal is simply to have the browser display a bounding box around the rendered geometry.

Here it is again:

>     ======================================
>     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."
>     ======================================

Perhaps better:

"When displayBBox is true, the bounding box is displayed for the associated geometry. The bounding box is displayed regardless of whether the associated geometry is visible."

Phrasing improvements and complete clarity is always welcome.   8)

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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