# The Naked Scientists Forum

### Author Topic: Perceived speed of moving objects at a distance due to parallax effect  (Read 1780 times)

#### akiskalo

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##### Perceived speed of moving objects at a distance due to parallax effect
« on: 25/07/2012 16:15:26 »
Hi I have an object going from point A to point B(40m) at 1.6 sec while the observer is standing still and perpendicular 19m away from it.
I was wondering if there is a mathematical formula that when applied could enable us to simulate the perceived speed of that object moving across our retinas, but at a smaller distance from it?
In other words how much would one need to slow this object down in order for its perceived speed at say 3m would be the same as at 19m?
Sorry if it sounds confusing, I am sure its very easy to anyone who has experience in this field.
Its for a simulator that I have made and I just cant get this part right as I refuse to guessetimate it.
Any help will be greatly appreciated.

#### Geezer

• Neilep Level Member
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• "Vive la résistance!"
##### Re: Perceived speed of moving objects at a distance due to parallax effect
« Reply #1 on: 25/07/2012 17:07:38 »
The speed difference will be proportional to the ratio of the distances. In the example you give, multiply the speed by 3 and divide by 19.

#### akiskalo

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##### Re: Perceived speed of moving objects at a distance due to parallax effect
« Reply #2 on: 25/07/2012 17:17:16 »
I have done that since my simulator is a scaled version of the real thing.
However although the speed is also to scale as you suggested, due to the fact that the observer is closer to the projectile the motion parallax effect makes it seem much faster than it actually is.I need to slow it down slightly so that to the observer it seems to have the same speed as the full scale version.

#### Geezer

• Neilep Level Member
• Posts: 8328
• "Vive la résistance!"
##### Re: Perceived speed of moving objects at a distance due to parallax effect
« Reply #3 on: 25/07/2012 18:04:12 »
I think the distance between the eyes always reveals the true distance from the object through triangulation, so there really is no "right" solution to the problem (without also scaling the distance between the eyes, which might be a bit tricky!) If that's true, you will have to adjust things until it looks as good as you can get it.

#### akiskalo

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##### Re: Perceived speed of moving objects at a distance due to parallax effect
« Reply #4 on: 25/07/2012 18:47:37 »
Thank you again for your replies.
I have been battling with this for a while now and could also only come up with whatever looks the closest to the real thing.
I have everything to scale and the maths of it and algorithms  for my little program work very well, with the exception that the proximity to the projectile gives a false sense of it moving faster then it really is.I was hoping that there would be a precise mathematical process to work this out, but I guess an estimate will have to suffice.
Thank you all for your help.

#### The Naked Scientists Forum

##### Re: Perceived speed of moving objects at a distance due to parallax effect
« Reply #4 on: 25/07/2012 18:47:37 »