4 points tracking with one hidden ?

Become a member of the CGSociety

Connect, Share, and Learn with our Large Growing CG Art Community. It's Free!

THREAD CLOSED
 
Thread Tools Display Modes
  09 September 2004
4 points tracking with one hidden ?

Hi again !
I need to track a paralepiped that have one corner hidden by the hand of a character, actually it's the sceen of a mobile that I need to replace.
How do you get the 4th point's motion in order to apply a corner pin effect ?
In after effects there is the parallel-corner-pin effect to do that.
I was thinking of looking for an expression to retreive this missing point but I'm stuck...
__________________
Georges' biggest fan
http://www.seb4d.com
 
  09 September 2004
Just track it as close as possible to the point and then just offset the track with a move 2d.
__________________
-deke
 
  09 September 2004
Ok actually this is not as easy as it seems.
What I need is to replace a mobile screen by a virtual one, so I need to track the corners to apply a corner pin effect to the virtual screen. But one corner is hidden by a hand, actually a big part of the screen is hidden.
I was wrong when I said "paralepiped", a rectangle seen in perspective is not really a paralepiped, oposite sides and angles are not equal. The mobile screen is a 3D object projected on a 2D plan.

I think the equation is too complicated for me. The tracker returns the x and y coordinates of the 3 corners but is it enough information to calculate the fourth corner ?

__________________
Georges' biggest fan
http://www.seb4d.com
 
  09 September 2004
Hi seb4d,

Can't you track the 4th point by hand?

If you have three points visible all the time shouldn't be that hard to figure out where the fourth one should be to manually track it.

Case you shot is shaking too much to try to go manually, you can stabilize it first, do the four corner and then put back the shaking in both elements.

Just an idea


Cheers,
__________________
diogo girondi | ••• | IMDB
 
  09 September 2004
This could be a solution yes, but I was hoping there was a way to do that automatically because this kind of shot often happens it would save a precious time.
__________________
Georges' biggest fan
http://www.seb4d.com
 
  09 September 2004
yes, i tend to stabalise my footage and then reverse the transform, it easier to see what its doing, also if you are having problems with tracking points disapearing, take a look at this post, http://www.cgtalk.com/showthread.php?t=164422Aneks points out something i had missed while learning tracking. The tracking point offset button allows you to put your track point where it should be, and then offset where it tracks, this was useful in a project where i had to replace a poster on the wall, while people were walking infront of it constantly, it worked in that situation because it was a long shot with a hand held camera but the camer stayed parralel. If you are unlucky enough to have a camera shot with lots of changes in perspective, this technique becomes less useful, as the further away from the orriginal point there will be a greater difference in relation to the orriginal movement, (that probebly doesn't make a lot of sence)

I have tried manually corner pinning, and its not a pleasant or very pretty way of doing it. Thats when i run and use 3d tracking instead
__________________
advirtising whore at the moving picture company
http://www.moving-picture.com

Don't eat muffins when i am developing you!
 
  09 September 2004
Yes ant- , I know the tracking point offset but unfortunately this does not the trick because of the complex motion of the screen to track.
I think I'll have to go with manual work.


Thanks for your help guyz !
__________________
Georges' biggest fan
http://www.seb4d.com
 
  09 September 2004
i don't know if you have access to 3d tracking with boujou or PFTrack or something, but the automatic tracking can work out motion from hundreds of points, I have used this techniqe sometimes, and then just rendered out a grid from a 3d program and tracked that with shake. Long way round, but more accurate.
__________________
advirtising whore at the moving picture company
http://www.moving-picture.com

Don't eat muffins when i am developing you!
 
  09 September 2004
Yes this sounds like a good alternative, it deserves to be tested !
Thanks !
__________________
Georges' biggest fan
http://www.seb4d.com
 
  01 January 2006
Thread automatically closed

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.
__________________
CGTalk Policy/Legalities
Note that as CGTalk Members, you agree to the terms and conditions of using this website.
 
Thread Closed share thread



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
CGSociety
Society of Digital Artists
www.cgsociety.org

Powered by vBulletin
Copyright ©2000 - 2006,
Jelsoft Enterprises Ltd.
Minimize Ads
Forum Jump
Miscellaneous

All times are GMT. The time now is 05:37 AM.


Powered by vBulletin
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.