The Path Duplicator is one of the most sophisticated and powerful ones. Its purpose is to make it easier to create tube-like structures such as pipes, corridors, and paths, by giving you independent control over the cross-sectional shape of the structures, as well as the path it takes (so it's sort of like an 'extrusion' function in a 3D modelling program). It overlaps in functionality with the 'Extruder'.

When you select the path duplicator from New Polyhedrons|Duplicators & Misc and drop it into the map, you see the red 'group selected' square plus a lot of dotted outlines. That's because a group is what has been dropped into your map, and therefore selected. If you look at the group in the treeview, you'll see that it contains one Path Duplicator, and three Path Points. If you then select the Path Duplicator, a bunch of handles will become visible, one regular duplicator handle, and three squarish ones, which appear to be located at the 'bends' in a structure. Drag them around & you'll see that this is indeed the case.

Plus you can RMB on these handles to get menu items to remove them, and add new ones, thus getting lots of control over the shape of the path.

The path of what? It's actually a tube, defined by an ordinary positive brush and a negative one, you can see them by expanding the Path Duplicator and then inside of that the group named Template. What's happening is that the brushes inside the duplicator are taken as defining the cross-sectional outline of the shape we're going to make, with the X-direction being lengthwise.

The brushes don't have to be inside of the Template group, and there can be duplicators there as well, so the cross-section could involve some complicated structures (it could be a row or grid of pipes, for example).

It is also possible to have a structure that is replicated, or 'tiled', along the length of the corridor. Any such things are placed inside a group named 'Tile', which is treated specially: brushes in this group don't have their front and back faces stripped off, & the entire contents of the group is copied along each branch of the path as many times as the entire X-axis length of the stuff in the Path Duplicator will fit (the contents of Tile are treated just like other contents of the Path Duplicator for working out the size of the template).

Sometimes you might want to create some sort of complicated sub-assembly to connect the segments of the path duplicator (for example to solve texture alignment problems by having custom textures on the joins). Elbow-space can be created with the 'squarend' and 'setback' specifics (of the duplicator itself, not the containing group).

Next, if the angles of the joins are all the same, you can use the 'elbow' duplicator to make multiple copies of the joining structure, suitably rotated. Pushing the elbow button drops an elbow duplicator into the group, which uses the same path points as the path duplicator itself. Into this duplicator put the structure you want to be replicated at the elbows, locating it at the first elbow (space between first and second path segments). It might be easier to line things up if you dissociate the images of the path duplicator first; then you can use tag & glue operations to join things up (I have tested that the results can seal against the void).

Combined use of the elbows and the 'level' specific could be a reasonable way to deal with the problem of making a corridor or path that both rises and turns (horizonatally) at the joints, without twisiting.

I wanted to share this idea I had for a (possibly) different use for the path duplicator. Maybe everyone already does this, but just in case...

I used to think of the path duplicator as a tool for constructing hallways or piping or other symmetrical extruded objects. But it also works very well for constructing non-symmetrical things like rooms.

For example, instead of using symmetrical, closed objects for your template (like the shape of an "O"), try cutting your template in half down the middle (so that it's now shaped like a parenthesis) and constructing your tunnel out of two halves. This makes it very easy to widen your tunnel as you go, or have it open up seamlessly into a room. In fact, using this method, you can use your template to create an entire oddly-shaped room by extruding the template all the way around in a loop. Drop in a ceiling and a floor and voila! You have yourself an oddly shaped room with almost no work at all.

You can create some really cool rooms this way if you get creative with the template. For example, try making your template into the shape of a capital "E" and extruding that in a loop. Suddenly you have a room with a walkway around the edge.

Anyway, this is how I've taken to making all my maps these days. I keep a set of stylized cross-section prefabs that are all multiples of the same size and can be used in different areas of the map. I hope this comes as news to at least a few people. It has certainly made map-making a lot more fun for me.