[x3d-public] OrthoViewpoint fieldOfView - and display size

Don Brutzman brutzman at nps.edu
Sun May 6 22:28:39 PDT 2018


Thanks for multiple helpful postings on this topic.  Offhand I'm not remembering special rationale involved.  Good question for CAD experts where OrthoViewpoint view is more commonly used.

X3D Tooltip:
http://www.web3d.org/x3d/content/X3dTooltips.html#OrthoViewpoint.fieldOfView
=========================================
[fieldOfView accessType inputOutput, type MFFloat CDATA "-1 -1, 1 1"]
Minimum and maximum extents of view in units of local coordinate system. Small field of view roughly corresponds to a telephoto lens, large field of view roughly corresponds to a wide-angle lens.
Warning: minimum corner must remain less than maximum corner.
Hint: rectangular display width/height = (maxX-minX) / (maxY-minY)
=========================================

If someone wants to collate everything posted regarding OrthoViewpoint fieldOfView into a proposed specification-text prose change, am happy to use that to establish a Mantis entry that tracks this issue.  Important to list options and tradeoffs when doing so.

As far as going from a 4-tuple to a 2-tuple for fieldOfView, and considering default values, and considering fractional or unit based, there is no better time to pursue such a change than when going to X3D v4 which indeed allows such modifications - when justifiable.

May I suggest that someone look into SVG and HTML to see if there is some potential benefit to changing our representation to better match with an existing Web design pattern.  X3D authoring would remain really awkward if a broader norm exists and our norm is different (or difficult to map) for no good reason.

Am finding a number of OrthoViewpoint issues already in Mantis when searching, but none seem particularly relevant to this point.
http://www.web3d.org/member-only/mantis/search.php?project_id=4&search=OrthoViewpoint

Of course having fieldOfView values that are fractional to screen size actually begs the point somewhat if screen size remains unknown...  Rechecked mantis, not finding any issues relevant to screen size.
http://www.web3d.org/member-only/mantis/search.php?project_id=4&search=screen

Am thinking that being able to determine display screen size at run time ought to be part of SAI for authors, and just rechecked, but am not finding it.  The Browser services list is lengthy but doesn't have that:

6.3 Browser services
http://www.web3d.org/documents/specifications/19775-2/V3.3/Part02/servRef.html#BrowserServices

Related: a number of years back I started exposing Browser functionality in a "Scene" prototype, trying to expose SAI functionality that otherwise required scripting to expose in a scene.  It includes several "wish list" parameters including pixelHeight and pixelWidth.  Incomplete/imperfect trial:

- Basic X3D Examples Archive, development, Scene Node Prototype
   "Expose functionality of Browser class in Java/ECMAscript annexes of VRML 97 specification. Consider promotion to a native node in X3D/VRML 200x scenes."
   http://www.web3d.org/x3d/content/examples/Basic/development/SceneNodePrototypeIndex.html

I frequently see HTML or tablet/phone app examples that require knowledge of screen size to properly function from a user perspective.  Always left with impression "X3D needs those parameters from browser" or X3D scenes cannot be similarly effective.  Historically, past browser-builder companies could never seem to agree on resolution (or even need) to handle the issue, and so this remains a gap...  am guessing that this definciency is why OrthoViewpoint.fieldOfView is weakly specified.

So, suggestion: let's fix both OrthoViewpoint.fieldOfView and Browser screen size together, consistently, if possible.  Aligning well with HTML or SVG or current practice in apps will simplify X3D authoring and integration.

Am also happy to dedicate X3D Working Group teleconference discussion time if that can help.  This is an excellent opportunity for progress, thanks for considering the possibilities.

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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