POV-Ray : Newsgroups : povray.advanced-users : Optical Pendulum : Re: Optical Pendulum Server Time
28 May 2022 00:38:20 EDT (-0400)
  Re: Optical Pendulum  
From: Francois LE COAT
Date: 13 Apr 2022 11:50:28
Message: <6256f144$1@news.povray.org>
Hi,

Mr writes:
> Francois LE COAT wrote:
>> Do you know something about the experiment of the "Optical Pendulum"?
>>
>> A camera is suspended upon a cable, and an image is shot at the rest
>> position. Then you push the pendulum, so that the camera oscillates,
>> and new images are acquired when the pendulum moves. The goal is to
>> evaluate the eight parameters that describe the position of the camera
,
>> from the rest position to the actual one. Because the pendulum
>> oscillates, we obtain pseudo-sinusoidal curves.
>>
>> The eight parameters are the perspective transform that happen
>> from an image, to the others. That means translations <Tx,Ty,Tz>
>> rotations <Rx,Ry,Rz> and two perspective parameters <Sx,Sy>. That's
>> what we can see in bellow video. Each images, and the corresponding
>> perspective transform parameters, compared to the rest.
>>
>> The goal is to measure a global movement, when it is observed by the
>> camera. There are devices that determine the position, such as the GPS

>> (Global Positioning System). We can evaluate rotations with a gyromete
r,
>> the accelerations with an accelerometer, the speed with an odometer.
>> The goal is to measure all this by the image, with a camera. Why?
>>
>> For example when we send robots to the planet Mars (Perseverance and
>> Ingenuity recently), and we want to pilot them with the means at our
>> disposal... On planet Earth there is a positioning system by GPS, whic
h
>> works with a network of satellites. But on Mars it does not exists. To

>> navigate on Mars, we find our way with a camera. To do this, you have
>> to measure the movement of the camera. This is the goal of our
>> experiment. Measuring the movement of the camera... The robots that
>> move on Mars have navigation cameras. These are their eyes. It's as
>> efficient as a GPS.
>>
>> Here is the video demonstration, with the optical pendulum experiment:

>>
>>       <https://www.youtube.com/watch?v=PXbWNW7duCY>
>>
>> We can see the image taken at the pendulum's rest. Then each of the
>> images, when it oscillates. We see the perspective transformation
>> between each image, to the rest, in image plane, i.e. in two dimension
s.
>>
>> Then using the parameters obtained in 2D from the transformation, a
>> virtual camera moves in 3D, using Persistence Of Vision software.
>> It is an illustration of the use that we can have in 3D of the
>> parameters: in translation <Tx,Ty,Tz>, in rotation <Rx,Ry,Rz> and
>> in perspective <Sx,Sy>. It is a question of determining from the image
s,
>> the movement in space of the camera. The movement in space between two

>> images is completely described by eight parameters. POV-Ray is very we
ll
>> suited to represent the trajectory in 3D, because it is a free image
>> synthesis software. Of course, all these computations are not yet done

>> at the rate of video. It will probably be necessary to design a hardwa
re
>> acceleration, to obtain a smoother video...
> 
> This reads as what a 3D tracking software such as the one shipped in Bl
ender
> would do ?

I haven't seen such a tool yet. There's software to perform image
stitching like <http://hugin.sf.net/> which are registering images,
but it is not giving perspective transformation parameters. The goal
is to compute those perspective parameters, in order to reconstruct
the motion of the camera:

	- <Tx,Ty,Tz> translations in pixels
	- <Rx,Ry,Rz> rotations in degrees
	- <Sx,Sy> perspective in degrees

This can be directly used in Persistence Of Vision for animation.

Is that what you meant?

Thanks,

Best regards,

-- 

<http://eureka.atari.org/>


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