I could use some expresssion help

[Seriphu]

Hey everyone, ive been digging around for hours trying to find the formula to calculate a position and offset of a square. In my case a monitor screen. I have a shot where there is a monitor on a table at an angle with a slight camera push. Ive tracked and stabilized the shot, but my main problem comes when halfway through the shot a hand crosses over both corners of a laptop while it closes. The laptop is the hero and getting the cornerpin to lockdown is proving counter intuitive without any sort of perspective line reference.

Im pretty sure that I can figure out the position of both points and use the data of my two locked tracking points. Ive tried dividing both top and bottom left points by 2 individually then subtracting the two to get the difference down the middle. Ive also gotten the center point of the monitor, I just cannot seem to get the two corner points. It is taking up too much time trying to figure it out so im going back to hand animation, still for the future I was hoping to see if the expression masters of the community could lend me their aid.

Thanks as always!

[adamghering]

im not anexpression master but i might be able to solve your issue without using expressions. make a card in 3d space an put the pivot at the relative space where the laptop hinge rotates from. this may be slightly behind the card or in front a mm or two depending on the laptop. look at this on the physical model. then animate the card rotating from that pivot point just like the screen. this will require far less noodling and the perpective should be perfect. you can then apply the image to the card.

hope this helps. the issue with an expression is that it would require more than simple math to look correct. especially for one piont arcing in 3d perspective space; you also have the speed velocity of the closing monitor itself to contend with. if it were not such an extreme 3d perspective then itmight work, but i imagine it would be pretty diificult once the visible area shrinks as it closes.