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get outside shape

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the background object has some parts.
ex) tree, house , Rock, snow, cliff , ... and so on.

they has some intersectes each surface, and empty space.

How we get outside-shape?(one-skin-mesh, like one-Volume.)

Boolean or VDB_Combine?

I cannot delete inside empty space.

any options?



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Greetings , 

If this is for 2d bg like in the image one way i think can solve this is by extracting the longest border . Game Dev tools has great extract border tool that can help . then Measure the area of each connected prim ( sumed  for each connected )  , and delete all prims that dont have the maximum perimeter , leaving only the longest prim which is likely the outside border . attached is image showing an example of the node structure : 


in case the actual scene your working with is 3d and not a 2d background can apply similar method of only keeping the largest connected primitive ( thus discarding the separate interiors ) . 

For Each Connected Prim > Measure Area > Promote Area to detail ( SUM ) > promote Area back to prims ( first match ) . Then after the for each loop Promote Area to Detail ( Maximum ) and remove prims that dont have the largest area 

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my scene is 3D with complex scene.

I understood the way of thinking.
I am not used to Houdini, so it will take some time. I will try in your way.

I will post the file if it works.

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VDB should do the trick. Booleans are also good option. Probably I'd used booleans for exterior part, and VDB for interior with some peak node usage (like a push in max, inflate in zbrush) and combined it with exterion via boolean/union.

Also convexhull may help in some cases. It really depends in a given situation

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