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motion tracking over long distances/with steadicam


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#1 Sebastian Matthias

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Posted 10 May 2005 - 02:39 PM

hey everybody!
i´m new to this forum ( come from the steadicam-forum) and have a question concerning motion tracking. i have a shoot coming up in a big (very big / 800 sqare meter !)studio.the shot will be steadicam and, since sytems like thoma´s walkfinder (infrared-leds+infrared cameras) have limitations in hight and width we want to use a motion tracking program to feed the shots into the motion control afterwards. we allready looked into bujou bullet and some other programs and the post-superviser+the dop don´t think that those softwares would work in a big studio over long distances and also would not be exactly enough to use with the moco+models later on.
has anyone of you done something like this before ? would it help if we made the tracking balls just 3times the size or are there any systems around (not sensor based!does not work with steadicam) that can track the pictural motion over a long distance?

would be nice to get some feedback !

all the best

sebastian
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#2 Laurent Andrieux

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Posted 10 May 2005 - 04:05 PM

Hi !

Maybe you should ask this in the post production section (if you haven't already).

I would say you are right about the idea of making the marks bigger. I would say the whole problem is the question of the marks being readable by the software.

I've been doing tracking in "normal" conditions, but I know that people at Megamount have made tracking on helicopter shots at some distances that were high upon 800 meters (the crosses being just hudge ! like 10 by 10 m) for moco and it worked (on some car advert, I can't remember wich one, sorry).

It wouldn't be so difficult to just test something in video in ext day at a long distance, with big balls, would it be ? hand held with a dsr 500 would be fine enough for it... Think it would be worth trying...

just a 2 cents, again, I never did such a shot...
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#3 Bob Hayes

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Posted 11 May 2005 - 06:33 AM

Interesting question.

I have seen these little motion tracking sensors. Instead of visually recording their x, y, z they send a signal telling a computer where they are in relation to other fixed transmitters. Look into mounting three on the camera and then placing some on key elements of your set. You might get you image close enough to match it.
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#4 Sebastian Matthias

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Posted 11 May 2005 - 02:27 PM

hello all! Thanks for your replies!
the real problem with tracking steadicam is that you have 6 positions to look at. pan,tilt,roll,booming up and down,backward/forward and accellaration. and everything has to very,very accurate to feed it into a moco.(especially when you work with models and not a 3-d image that you can manipulate in a computer). the helicopter thing sounds very interesting,alltoug in a blue/green studio you don´t have any other markers than the tracking balls/crosses. maybe that would be really the best way to make the markers just very big.
would you stll be able to erase them from the picture later on in the post if they are big?

thanks for input!

cheers

sebastian
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#5 Laurent Andrieux

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Posted 11 May 2005 - 03:34 PM

Once again I think a post production specialist could answer this question but actually it's not the real size of the marks that count, it's their size in the image so I would say a one foot mark at ten meter is not a bigger problem than a ten meter one shot at 500 meters you see...
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#6 Mark Allen

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Posted 11 May 2005 - 04:22 PM

You can use multiple sets of markers. In tracking them, you would change your marker set and then line up the change points. It's not a one click deal of course, but it's possible. If your several pixel tracking marker becomes the size of a basketball - you're not going to be able to track to it anyway.

If you're on a chroma stage then there will be noting else to track to but markers - so they will be key to have. If you're on a set that might have a hallway or something, you can often find objects in the hall to lock onto.

For this kind of shot you definitely need to bring a visual effects supervisor in to consult with you. Or at least the compositor who will be doing the shot. Setting it up right will be a huge financial savings for the producer in post side.

added later:

If the first paragraph wasn't clear - what you would end up having is a series of markers along your path, like a two level air strip. If they can be kept out of the range of moving actors - all the better - other wise it will require a touch of roto.

Edited by Mark Douglas, 11 May 2005 - 04:24 PM.

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#7 Kai.w

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Posted 12 May 2005 - 07:32 AM

hello all! Thanks for your replies!
the real problem with tracking steadicam is that you have 6 positions to look at. pan,tilt,roll,booming up and down,backward/forward and accellaration. and everything has to very,very accurate to feed it into a moco.(especially when you work with models and not a 3-d image that you can manipulate in a computer). the helicopter thing sounds very interesting,alltoug in a blue/green studio you don´t have any other markers than the tracking balls/crosses. maybe that would be really the best way to make the markers just very big.
would you stll be able to erase them from the picture later on in the post if they are big?

<{POST_SNAPBACK}>

I did something similar as a test some time ago. Rather slow handheld camera walk. Its possible, but you have to be sure you always have a good amount of markers in frame, so you'll probably lose some over time, make sure others come in for that. You have to practise the movement for sure and have someone resposible for the tracking present to take a look.

here are some good tracking tips I like to refer to:

http://www.fxguide.com/fxtips-273.html

-k
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#8 Sebastian Matthias

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Posted 12 May 2005 - 08:30 AM

hello everybody !
thanks for the replies !
and kai: thanks for the link!there´s some interesting stuff there!

cheers

sebastian-doesn´t-know-how-but-will-find-out-matthias :blink:
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