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I have this strip on my landscape that I want to make disappear from where the digger currently is, and then following the digger towards the end of the strip, to reveal the trench underneath.

What is a good way to do this? Can I animate an object that removes the ground strip? The camera is static in this scene so I could also imagine using a mask, or doing something in the video sequence editor.

*Cutting out my strip (knife project) messes up the connection with the rest of the landscape (they both have displacement maps). So I think I need to keep both images and animate a mask in the video sequence editor or something.

Scene without trench

Scene with trench

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To get the cleanest result I suggest animated booleans. Since you have flat shading you wont get any shading artifacts, this is probably the textbook example for them. If you have some subsurf and displacement apply them or put the booleans after the displacement.

There will be 2 boolean objects.
- First one is static and will create the hole in the ground (highlighted). Put some edgeloops in the ground object around the trench so this boolean wont segment the whole thing.
- Second one can be just an animated cube and will intersect with first boolean object and the concrete wall inside trench. The bigger the intersection the more ground will be removed and more concrete wall will be shown.

enter image description here

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  • $\begingroup$ I still have the problem here that the displaced mesh deforms when I cut my strip. I can't apply the displacement modifier, because the large area has a huge subsurf and displacement. I'll try to isolate it to the frame area and then apply them. $\endgroup$ – cybrbeast Dec 5 '14 at 9:28
  • $\begingroup$ I see, but you should really get rid of subsurface because the model is so simple. Things get easy when you have only real geometry. And if there is only real geometry and the displacement is not animated it can be applied and gotten rid of. This would make your struggle so easier. $\endgroup$ – Jaroslav Jerryno Novotny Dec 5 '14 at 9:36
  • $\begingroup$ While it might not look like it, the displacement certainly there and the subsurf is needed. The displacement map is from a very accurate height map 0.1m resolution. It cause the ditches to be where they are. I agree that here it's not that necessary, but this is zoomed in from a larger scene, and if I remove it here you would see a weird discontinuity. $\endgroup$ – cybrbeast Dec 5 '14 at 9:38
  • $\begingroup$ I think I managed to fix it. I cut out a context area around the frame, applied the subsurf and displacement there. It looks the same as the normal situation now. Now I'll try your method. $\endgroup$ – cybrbeast Dec 5 '14 at 9:42
  • $\begingroup$ Thanks for all the help. Having never used boolean much, I'm now having a problem that the moving cube still appears. Illustrated here: imgur.com/bDuk629 $\endgroup$ – cybrbeast Dec 5 '14 at 10:12
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You could try a reversed Build Modifier starting with a cube which has been duplicated by an applied Array Modifier.

enter image description here

Result:

enter image description here

You could also use hide planes by the Build Modifier to uncover the trench.

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  • $\begingroup$ The problem there is that my strip of land already has a displacement modifier shared with the rest of the landscape, otherwise it doesn't fit in. Could I cut it up in blocks and then do this? *Nevermind, the displacement is already messed up on the cut, as it doesn't connect well with the rest now. I think I need to do something with a mask in the video sequence editor, not quite sure what yet. $\endgroup$ – cybrbeast Dec 5 '14 at 8:45

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