[x3d-public] visibilityRange for X3DFogObject: specification erratum detected

[Michalis Kamburelis]

Hi,

I completely agree with Andreas proposed addition to define

"""
- fogVisibility (Table 17.5) is the currently bound fog's
visibilityRange, in the same coordinate system as fogDistance.
"""

> Michalis may have background on introducing the 'fogVisibility' term.
> Perhaps it is an attempt to decouple from the fog node to allow
> flexible use of world or local coordinate systems for computations.

I'm afraid I don't have any additional insight as to why it is called
"fogVisibility". It was already called like that in X3D 3.3, before my
PBR edits ( https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/lighting.html
) and it was also not explicitly defined there. So I neither broke nor
improved that state when editing that section for X3D 4.0 :) The
theory above from Andreas sounds good -- i.e. the term is called
"fogVisibility" to make it clear that it is not "just straightforward
visibilityRange" value, and instead it is "visibilityRange converted
(scaled) by the fog node transformation".

I believe the intention was always just like Andreas said, and it
matches CGE/view3dscene implementation too.

Regards,
Michalis

śr., 18 paź 2023 o 16:22 Andreas Plesch <andreasplesch at gmail.com> napisał(a):
>
> Hi Don,
>
> Thanks.
>
> > Andreas, if you have suggested prose for “explain that fogVisibility corresponds to the visibilityRange field” then please send that.  We can at least create a Mantis issue for eventual resolution.
>
> The table 17.5 at
>
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-IS.proof/Part01/components/lighting.html#t-foginterpolant
>
> mentions 'fogVisibility' but the term is not clearly defined.
>
> The bullet list above the table has
>
> - fogInterpolant is the fog interpolant, see Table 17.5 for calculation.
> - fogDistance is the distance from point on geometry to viewer's
> position, in coordinate system of current fog node.
> - fogColor is the currently bound fog's color.
>
> Let me suggest expanding that list with an additional line:
>
> - fogVisibility (Table 17.5) is the currently bound fog's
> visibilityRange, in the same coordinate system as fogDistance.
>
> Michalis may have background on introducing the 'fogVisibility' term.
> Perhaps it is an attempt to decouple from the fog node to allow
> flexible use of world or local coordinate systems for computations.
>
> Best, Andreas