If this is the effect you want, and your motion command is "translate 
x*clock" then you could just square the value of the clock. like this: 
"translate x*clock*clock*2 "

"Trevor G Quayle" <Tin### [at] hotmailcom> wrote in message 
news:web.44454d0399d124d66c4803960@news.povray.org...
> "danyolgiax" <d.o### [at] gmailcom> wrote:
>> Hi!
>>
>> Using motion_blur with a box runs along x axis I've seen this effect is
>> bidirectional! I've got a blur in front and at the end of the box!
>>
>> There's a way to make it uni-directional?
>>
>> Thanks!
>>
>> Daniele
>
> Actually motion blur works exactly the way it is supposed to.  In reality,
> for an object that is moving at a constant speed, each instance of the
> object has equal exposure time and equal weighting in the image.  This may
> give the impression that there is blur in front and in back, when really
> it's not, the the back of the blur is the object at the opening of the
> shutter and the front of the blur is the object at the closing of the
> shutter.
> What you are assuming that you should see would be for an object that was
> moving when the shutter opened, but stopped for some period of time while
> the shutter was open, giving that 'position' a greater weight in the
> exposure.  To do this (I assume this should work as I haven't actually
> played with motion blur in megapov), you would need to apply a function to
> the object tranform factor that gives a non-linear movement over the 
> period
> of time the blur is calculated.
>
> I hope this made sense to you and was helpful.  Coincidentally, I just 
> came
> across an article about this very subject the other day that was very 
> clear
> on the reasoning, but for I can't locate it at the moment.
>
> -tgq
>
>
>

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