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DaveMcD · Joined: 16 Mar 2005 Posts: 16

Hey All,

I'm looking for a couple of ideas to help align a particular bunch of shots I'm working on.

I have a 2000 frame long nose mount chopper shot flying along a freeway construction site ahich is about 10 km's long (footage is sped up prior to tracking 4x). I've tracked the shot and imported the 3D (from survey CAD) and manually lined it up by eye as best I can. I've been trying to find some recognisable points like edge of a road intersection which I can identify from the current level of construction. I was attempting to create these as seed points by using 'place' in the perspective view and resolve from seed points but it isnt seeming to work and appears to give me no solve at the end. With lining up by eye (in 3ds max) I can get a fair bit of the freeway to match but its quite wrong at certain points.I can either make the ends match and not the middle, or get one end and a middle to match but not the other end) My suspicion is that the solve isnt acurate over that distance and that it is slightly skewed or contracted, pinning some points might help to stretch that out (either that or the road they have started to construct has taken a wrong turn somewhere.

Is there another process I should be trying to use to create the points? Also considering that I may not be able to pick exact points can I get syntheyes to use them as suggestions and if so how many would I need.

any help appreciated I've actually got about 8 such clips to try to get working and make one long video of 70km's of freeway from.

Cheers

DaveMcD

ssontech · Posted: Mon May 12, 2008 12:12 am Post subject:

Camera matching is inherently subject to accumulating errors on long shots --- roughly you're measuring the change from one frame to the next, so if you have a long shot with new things coming and going then there's going to be drift. It's the same thing as trying to hike a straight line in the forest, or swim with your eyes closed. Slight systematic errors (lens distortion, off-centering) accumulate.

On this kind of project you should have periodic surveyed waypoints to match back into the 3-D model. Usually those are GPS'd.

Martin Smola has done some great work with highway previews.

lightfuzz · Joined: 03 May 2008 Posts: 9 Location: Arizona, USA

DaveMcD: Hey Dave, I'm working on something very similiar to your situation. It is described here: http://www.ssontech.com/phpBB2/viewtopic.php?t=670&start=0&postdays=0&postorder=asc&highlight=

For long shots my issue is seen here: http://www.vimeo.com/1020656
password: sr179

The highway mesh seems to scale or snap into place when a new pegged or seeded tracker comes into view. Is there a way to eliminate or ease this? I've tried seeding points, pegging points, and both to no avail.

Like you said, some areas look good others do not. This would seem to be a common usage for Visualisers and Civil Engineers. Not all highway shots are a mere 300 frames.

I would love to hear how you possibly resolved some of your issues.

Thanks.

DaveMcD · Joined: 16 Mar 2005 Posts: 16

Hey Lightfuzz.

I havent had any breakthrough on it yet, Our test footage is only being shown to the client now (it has a few errors in it but was fine to show all the model detail we were proposing)

My next step was to try and redo my solution with some more footage added to it to be able to seed some more unrecognizable points. I'll let you know how I get on. From reading your thread it sounds like you're doing pretty much what I was trying.

DaveMcD