Hi David,
I looked into the maths of single precision floats some times ago. I can tell you
that imprecision
in the pure mathematical sense will occur for decimal numbers of 6-9 digits or larger.
This range may
sound strange like why is it 6-9 and not >8. Too much to go into here but you can
look at my analysis
on http://client.surak.com.au/~chris/PrecisionInVRML/PrecisionInVRML.htm.
However, in practical terms noticeable jitter from using floats occurs a lot earlier -
like when you have
zoom factors in your scene of > 1-2,000,000. All this I determined for VRML, not
Java3D but the maths will
be similar for Java3D floats - VRML browsers use only single precision floats and no
doubles.
In Java3D I have recently been changing transforms and coordinates for helo flight
simulator from floats to doubles.
The result is that the movements are smoother. I haven't finished all the conversions
so
still got a way to go before it is 'dead smooth'. I.E. still have some jitter I find
unnacceptable.
hope that helps,
Chris
David Yazel wrote:
> Hi all!
>
> I have a question for the math inclined. I am experiencing a lot of what I
> think are precision issues in my overlay system when my view is 3000+ units
> from the origin. The transforms are these:
>
> ViewTG
> |
> ConsoleTG
> |
> Geometry
>
> The console transform is scaling at 0.0006202004979235267, which tranforms
> into image plate screen coordinates taking into account field of view and
> screen size. The geometry is all specified then using screen pixel
> coordinates, so using (10,10) for the pixel location for example.
>
> Turning the view causes the most wobble in the overlay, but translating also
> does it.
>
> What is the solution to this? I am using floats for the coordinates, would
> changing them to doubles help at all in this case? What about putting a
> transform between the view and the console transform which moves it to the
> origin?
>
> Dave Yazel
>
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