Selecting only the outside of an object

[bradcarvey]

I am using H15 and would like to select just the outside of a half pipe with thick walls.

Ultimately, I want to create groups for different parts of the pipe.  I have tried "Shift + L" and "Shift + R" to select an edge.  But I don't know how to get this to grow, without wrapping around and getting the edge of the pipe and the inside surfaces.

 

I could manually select the geometry, but this is an experiment for using very large objects that have millions of points.

 

Perhaps normals could be used as a selection tool?

 

Any suggestions?

[Maurits]

Well depending on the mesh.
You could use the "unshared edges" under the Edges of the group node. This selects all the edges that only have one polygon attached.
Another option could be to use the Bounding box option giving the box the position and size of the object bounding box.
In this case you need to resize the x, y, z  so the bounding box is slightly smaller then the object, this will select everything except the outside. Then simply invert the selection and your done.

Or as you said use the Normal tab and select polygons based on their normal angles although you might need to create multiple groups and later combine them..
For a better answer providing the object or a image of the object and what you want to select might help.