Match 2 moving points to 2 unmoving points

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glenn
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Joined: January 19th, 2007, 2:49 pm
Location: Granada Hills California

OK, I'm fairly new to expressions, so this may be asking too much of them...
To overlay moving footage onto a still...

I have moving footage and a still
On the still there are two fixed points.

Is there a way to make two moving points on the footage line up in 2d onto the fixed points on the still?

Since the two moving points move at different speeds and do not maintain a steady spatial relationship to each other, it would be necessary to scale the moving footage to keep them equidistant...

Maybe I need 3 expressions:
1) to scale the footage to make the points remain equidistant
2) to rotate the footage to orient the moving points (to the same up/down relationship as the still points)
3) to align the footage with the still

and maybe that's not the right order to do it?

Is this even possible? Trying to do this 'by hand' is driving me nuts, and I thought I'd run this past the expressions geniuses...

at least it might be fun to think about.

Thanks for any help!
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lloydalvarez
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glenn wrote:OK, I'm fairly new to expressions, so this may be asking too much of them...
To overlay moving footage onto a still...

I have moving footage and a still
On the still there are two fixed points.

Is there a way to make two moving points on the footage line up in 2d onto the fixed points on the still?

Since the two moving points move at different speeds and do not maintain a steady spatial relationship to each other, it would be necessary to scale the moving footage to keep them equidistant...

Maybe I need 3 expressions:
1) to scale the footage to make the points remain equidistant
2) to rotate the footage to orient the moving points (to the same up/down relationship as the still points)
3) to align the footage with the still

and maybe that's not the right order to do it?

Is this even possible? Trying to do this 'by hand' is driving me nuts, and I thought I'd run this past the expressions geniuses...

at least it might be fun to think about.

Thanks for any help!
Unless i am not understanding you correctly, why are you trying to do this with expressions instead of a corner pin track?

-lloyd
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glenn
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Joined: January 19th, 2007, 2:49 pm
Location: Granada Hills California

I don't see how I can do this with the corner pin effect.

For clarity and simplicity, I'll use a fictional example of what I'm trying to do

Imagine a rope that's flipping around in the air, and the two ends are the points I want to match the two points on the still footage

On the still footage, Imagine two doorknobs on two doors that are side-by-side...

I want the composition to ' a show a rope flipping around in the air with it's ends fastened to the doorknobs ' - never mind knots or whatever, the ends just have to be on top of the knobs.

I don't think I can do anything like this with corner pinning
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hype
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it's certainly possible to lock the ends of the rope to the doorknobs using tracking and applying the data to the anchor point and position/rotation/scale values. But, if the image of the rope is a still image and you want it to sag and have all kinds of rope dynamic movement, that's sounds REALLY hard.
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glenn
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Location: Granada Hills California

ok, it's not a rope, but imagine it is.

and 'the rope' isn't a still image, it is moving around almost at random

the moving footage has

two moving points, that move both up and down and side-to side

and I want to pin those moving points to two NOT moving points

which are not moving and are on what can be considered a still image.

The moving footage can be scaled however it needs to be to match the two points on the still, it doesn't matter how much, the distortion to the moving footage won't ruin the footage.

The stationary points are essentially on the same horizontal line.

Yes, it's really hard, at least it seems so to me...

That's why I asked for help.
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lloydalvarez
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glenn wrote:ok, it's not a rope, but imagine it is.
Hey Glenn,

Maybe if you post the footage we'll have a better idea of what you are talking about. Based on your description i still think that tracking/stabilizing is the answer, but again.. i might be misunderstanding what you are after.

-Lloyd
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glenn
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Joined: January 19th, 2007, 2:49 pm
Location: Granada Hills California

I finally finished doing it by hand, one frame at a time.
But thanks for all the help anyway.

the moving footage is in the file called gzrrrt in either of the following zip files

http://www.pbjs.com/stockstock/stockstock5_mpg.zip
http://www.pbjs.com/stockstock/stockstock5_mp4.zip

The still is from one of the first 3 frames in the file called robot

I'm attaching the 'spark' to the two features at the left side of the wall

like I said, I did it by hand, but I'd be interested in ideas on any easier way to do something like this. I'm not very good at after effects yet...

I'm a (formerly retired) clown, and trying my hand at a career more suitable for someone my age... and out-of-shape condition. Clowning is too strenuous for me these days.
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lloydalvarez
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Hey Glenn,

Now that i see your footage i get what you want to do. Personally I would have done it by hand as well, so don't feel bad for having gone that route. But so that you can understand a little more of how expressions work.. expressions work with numbers and data within the AE application. They have no way on their own to actually "analyze" video. So what you need to do is convert the video into numbers that expression (or a plugin) can use. You can do this with tracking. Tracking "analyzes the video and converts it to x/y data that you can then use with an expression or plugin.. in your case you could try using some distort filters to lock the lightning bolts to the switch.. but due to the low quality of the video.. doing it by hand is probably the best way to go ..

hope that helps,

Lloyd
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lloydalvarez
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Hey Glenn,

Now that i see your footage i get what you want to do. Personally I would have done it by hand as well, so don't feel bad for having gone that route. But so that you can understand a little more of how expressions work.. expressions work with numbers and data within the AE application. They have no way on their own to actually "analyze" video. So what you need to do is convert the video into numbers that expression (or a plugin) can use. You can do this with tracking. Tracking "analyzes the video and converts it to x/y data that you can then use with an expression or plugin.. in your case you could try using some distort filters to lock the lightning bolts to the switch.. but due to the low quality of the video.. doing it by hand is probably the best way to go ..

hope that helps,

Lloyd
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glenn
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Joined: January 19th, 2007, 2:49 pm
Location: Granada Hills California

Yes, I tried tracking the 'end' of the sparks and no matter what settings I tried, it wandered all over.

Since it was so short, I figured it would be easier to do it by hand and skip trying to spend the effort on finding an 'easy way'.

I'm beginning to see that expressions are a bit different than I had first thought, and that's a good thing. Thanks for the help.
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