It looks like I'm treading ground that's been settled for years.
I thought your link to the entities class was going to solve my problem, but...
I'm trying to construct component definitions out of several previously defined components, but without placing any physical objects.
Here's one of those definitions:

` # Make the bottom plate
bottom_plate_def = Sketchup.active_model.definitions.add "Bottom Plate"
bottom_plate = bottom_plate_def.entities.add_face pt # pt is an array of points

Move the origin to center of final 3D cell

tr = Geom::Transformation.translation [-oal/2, -oaw/2, -cell_thickness/2 + plate_thickness]
bottom_plate_def.entities.transform_entities tr, bottom_plate`

Now, how do I combine three such definitions (bottom_plate, core, top_plate) into a fourth one? The entities class doesn't seem to allow it. But it must be possible, since it's a straightforward operation in Sketchup itself.

three_d_cell_std_def = Sketchup.active_model.definitions.add "3D Cell - Standard"

three_d_cell_std_def = Sketchup.active_model.definitions.add "3D Cell - Standard"

@tig said:

Use guide-lines or points at the two locations.

I guess I wasn't clear enough. That's what I do. The problem has been that with the move tool engaged I've been unable to reach the destination point. I've discovered that with the move tool dragging the object around it's still possible to zoom, pan, and rotate the point of view. That has helped some, but I'm still constantly running into situations where I just can't seem to select the destination point, no matter the gyrations I try.

The main trouble is with destinations points surrounded by existing objects. The move tool doesn't like to allow movement into those tight spaces unless I do it in stages with the viewpoint nearly parallel with with each of the three axes.

This is in the newbie section instead of the wishes forum because someone might know a good technique I'm unaware of. My problem is in drawings that depart from the rectilinear bias of SketchUp. Often my solids are complicated shapes and not referenced to the orthogonal axes. I need to move entities to arbitrary points in space, so what I really need is an ability to select an arbitrary destination point, select a group or component and a point within the group or component which is to coincide with the destination point.

The usual way I accomplish this is to align the viewing angle with each axis successively and do three separate moves. This is very tedious and sometimes impossible because the destination point is visible only from certain angles and the structure is too complex for x-ray or wire frame mode to be useful.