[x3d-public] Interesting max/round off issue

[Don Brutzman]

John, such a tolerance might be relevant within an engineering
application.  However there is no such way to express that within a data
schema.  Thus the careful selection of limit values for data validation, to
align with the authoritative X3D Architecture specification, remains the
appropriate response.

As ever, limits in X3D XML Schema are used to produce X3DUOM, which
(someday) will be used to produce an X3D JSON Schema.  The limit values are
also used in our APIs for Java and Python.  Thus keeping everything aligned
makes good sense for continued consistent X3D modeling across file formats
and programming languages.

In the meantime, it is certainly not a "false positive" diagnostic to learn
that some values in your models might be greater than required limits of
pi/4, pi/2 or pi.  Identifying such values does not hurt and might prevent
a later error in another application.

all the best, Don
-- 
X3D Graphics, Maritime Robotics, Distributed Simulation
Relative Motion Consulting  https://RelativeMotion.info


On Sun, Mar 1, 2026 at 8:47 PM John Carlson <yottzumm at gmail.com> wrote:

> Another thought is to create (physical) tolerances (error bars) of maximum
> and minimum constraint values, which would allow more realism, but that’s
> probably a lot of work.  So, pi/2+/-0.001.
>
> Thoughts?
>
> John
>
> On Sun, Mar 1, 2026 at 12:02 PM Don Brutzman via x3d-public <
> x3d-public at web3d.org> wrote:
>
>> Thank you for suggestion that we might change boundary values for our
>> numerical validation limits.
>>
>> I would be reluctant to change limit for pi/2 to “2” , since that could
>> be a mistaken model entry for 2 degrees, which is a case that does need to
>> be caught as a validation error.
>>
>> I think a limit of 1.6 would be OK, that would be forgiving of roundoff
>> errors and permit functional content, also providing a hint for numerical
>> value of pi over two.
>>
>> Similarly, we might make the validation limit for pi as 3.2.
>>
>> Meanwhile, we should probably keep specification boundaries unchanged
>> since they are reasonably precise and correct.  Most are defined in terms
>> of pi, double checking for consistency is always a good idea.
>>
>> Dick and I can discuss his topic at the next specification editors
>> meeting.
>>
>> all the best, Don
>>
>> --
>> X3D Graphics, Maritime Robotics, Distributed Simulation
>> Relative Motion Consulting  https://RelativeMotion.info
>>
>>
>> On Sun, Mar 1, 2026 at 04:46 Vincent Marchetti via x3d-public <
>> x3d-public at web3d.org> wrote:
>>
>>> I think this serves as an example of overeager validation, not overeager
>>> rounding.
>>>
>>> If validation is going to be a useful tool it should serve to warn of
>>> practical errors. The issue raised here could happen regardless of any
>>> additional rounding applied beyond that due to floating point
>>> representation.
>>>
>>> I suggest that a practical validation for this case would be to compare
>>> the groundAngle to 2.0 This will allow users to achieve the intentian of a
>>> groundAngle of pi/2 without giving false validation errors, and it would
>>> raise a red flag if the author mistakenly entered 180 for the groundAngle.
>>>
>>> It's always the code developer responsibility to catch mathematically
>>> invalid input values at run time.
>>>
>>> Vince Marchetti
>>>
>>>
>>> > On Mar 1, 2026, at 3:39 AM, John Carlson via x3d-public <
>>> x3d-public at web3d.org> wrote:
>>> >
>>> > Any comments on overeager rounding, which causes validation failures?
>>>  Maximum angle is 1.5708, which rounds off to 1.571, which is too big.
>>> Problem is with Background.groundAngle.  An argument for always validating?
>>> >
>>> > I didn’t notice an issue visually until trying to interpret schema
>>> validation issues.
>>> >
>>> > Any JavaScript filters for fixing overflows is welcome!
>>> >
>>> > As Joe says, sometimes you just want to go into user code and fix it.
>>> >
>>> > What if this had happened with .glb?
>>> >
>>> > John
>>> >
>>> >
>>> > Error below:
>>> > keyword: maximum
>>> > schema location: $defs > Background > oneOf > 1 > properties >
>>> @groundAngle > items > maximum
>>> > schema value: 1.5708
>>> > instance location: X3D > Scene > -children > 0 > Background >
>>> @groundAngle > 1
>>> > instance value: 1.571
>>> > instance shorthand value: 1.571
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