Can CG characters be made to realistically walk along a curved surface of a filmed 2D video clip?

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http://postimg.org/image/wti6ybpub/

Hi folks, let us assume we have a live action video clip showing a U-shaped river valley as per the picture in the above link. The video clip shot is a simple zoom in and camera pan move from left to right, such that when the camera move is done, the left face or left side of the valley is shown (currently the right side is visible in the picture). The dog is NOT present in the video clip. The final product is for us to have a CGI 3D dog animated and walk down the slopes of the valley from one end and walk across the shallow river and walk up the other side of the valley as per the purple dots which show the path to be followed by the dog.

We therefore perhaps track the video clip with pfTrack perhaps and then import the tracked results in Maya and we import our 3D model of the dog. Would we not be stuck at this stage? My reason for thinking this way is the fact that the video clip is a 2D live action clip and therefore, if we programme a walk cycle on the dog, he would simply appear to walk horizontal from one end of the valley to the other end and appear to walk or float in ‘thin air’ while directly over the middle of the valley. So I think I am concluding to assume that motion tracking live action footage and attempting to get CG 3D animals or people to walk on the ground surface in the footage, e.g. on a road or anywhere on the earth’s surface, I am concluding to assume that the surface must be flat in the video clip and cannot be curved, such as walking down a live action 2D valley or climbing over a live action 2D mountain.

Am I wrong with my assumption above? How can one make that dog walk down one side of the valley, cross the water, and walk up the other side of the valley in a realistic way where the viewer could not be able to tell that it was a CG dog but in fact make the viewer think that it is a real dog?

When you answer the above question, please say if your answered technique is essentially what the industry professionals generally do to achieve this realistic effect in feature films.

Also, the final aim is to comp. the video shot with the CG animated walking dog with comp. software - e.g. After Effects - i.e. if we have a solution to the above!

Thanks!

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You need to render an animation of the dog walking over the curve/slope in 3D software, adjust the 3D camera movement to follow the exact movement of your live action video. After that, in your comp software put the dog animation on top of your live action video.

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Thank you! I know it may be difficult at first but with practice, should be fine! Thanks for the simple explanation!

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Your welcome. It shouldn’t be that difficult I think. The downside of this technique is that you need to recreate the environment (although doesn’t need to be 100% accurate) so your dog animation will walk convincingly. This is the most common technique used in VFX studios.

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Thanks for the heads up. But in creating the rough environment, is it correct to assume that the environment mesh itself does not need to be animated (therefore it remains static) and the environment will look like it is moving (just like in the video) because we animated the 3D camera?

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Yes. You don’t need to move the 3D environment.

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Good thanks!