Item emerging from within a shot

#1

Dear all,

I am trying to make a short (14 sec) shot where a camera is flying through a canyon and I would like to make a 3D structure emerge into view as the camera goes over a rise and the canyon opens up.

I have tracked the shot, brought it into Modo, done the 3d passes, but when I get it into fusion I can’t work out how to “hide it” behind the rocks and make it visible as the camera crests the rise and flies into the canyon.

Probably a totally noob question, but if you could please signpost me as to where to look up a guide or a tut on DT, I would really appreciate it.

(I am using SynthEyes, Modo, Fusion (have access to Nuke if needed))

Thank you.

SJ

#2

a) you do a roto of the things which hide you CG asset and use that as a mask for the CG asset

b) you build a 3d model from the canyon, based on synthese pointcloud or even let build syntheyes the model and make adjustments in your 3d app
then use the model as a matte object in your 3d scene

#3

Glorious, this should be enough for me to get started, thank you.