As an example we take a cave passage with a pit in the middle of it and a lower passage departing from the bottom of the pit. The relevant piece of the centerline is:

survey test5
   ...
   survey s1
      ...
      input test5_s1.th2
   endsurvey

   survey s2
      ...
      input test5_s2.th2
   endsurvey

   ...
   join s2_l1@s2:0 s1_pit@s1:2
   join s2_l2@s2:end s1_pit@s1:6

   map map22 -proj plan
      scrap2@s2
   endmap

   map map5 -proj plan
      scrap1@s1
      break
      scrap2@s2
      preview above map22
   endmap

endsurvey test5

The drawing is made of two scraps: the first for the main passage, and the second for the lower passage. The walls of the second scrap are joined, with two join commands, to the lines of the pit in the first scrap. Each scrap is contained in one survey. The global survey defines two maps: map22 with the scrap scrap2 of the survey s2, and map5 for the presentation. This last map has two scraps on two different levels and a preview above command with the map map22.

Finally it is important that the configuration file contains the command to select the map map5. The map name must be "fully" qualified with the enclosing survey,

   select map5@test5

The outcome is shown in the next figure. Without the "break" command both scrap outlines would appear in the map. With the "break" you put them on different levels, and the first hides the second where they overlap. This is necessary because the map objects are scraps. It the two scraps were enclosed in maps that were the map objects, the top map would have appeared "above" the bottom one, and the break would have been irrelevant,

   map map11 -proj plan
      scrap1@s1
   endmap
   map map22 -proj plan
      scrap2@s2
   endmap

   map map5 -proj plan
      map11
      # break
      map22
   endmap

Without the "preview" (or with a "preview below") the outline of the second scrap would not be drawn in the map, and the drop would not be connected to the lower passage.

This example contains a passage passing under another. The first scrap has a crossway, The second scrap is attached to the right branch of the crossway and passes underneath the left branch.

This example shows a side passages departing from the main gallery and going backward and downward, passing below the main passage.

There are two scraps. The first scrap is the main gallery from the left to the right. The north wall is broken at the point the side passage starts with two lines, a "contour" and an "overhang". The latter has the option "-outline out" to tell therion that it belongs to the outline of the scrap.

The second scrap contains the side passage. It must join the first in three points: the two points where the north wall of the first is broken, and the other endpoint of the "overhang" line. The wall of this scrap is splitted in two lines to refer to the endpoints on the lines in the "join" commands. We could have used a single line and referred to the intermediate points in the "join"s.

    join s1_over@s1:end s2_l1@s2:0
    (or "-outline in") to specify that it belongs to the scrap outline
    join s1_l1@s1:0 s2_l2@s2:end
    join s1_l2@s1:end s2_l2@s2:0 

The next figure shows the result of this example. The colors have been added to emphasize the lines referred to by the "join" commands.

When you create the map of a complex cave it happens that one or more passages overlay on the map, thus making it hard to understand. The traditional way to handle this is to draw the outline of the minor passages (for example a dotted line around the contours) and draw them with all their features on the side. Dashed ot dotted connection lines are drawn to join the passage outline with the full fledegd drawing.

With therion you can achieve this by adding an offset to a map placed below another inside a container map. It is not possible to shift scraps, inside a map. Therefore you must collect scraps into maps and combine these maps into the global map, applying the shift where needed. For example,

  map m1
    scrap1
  endmap
  map m2
    scrap2 
  endmap
  map m12
    m1
    break
    m2 [0 8 m] below
  endmap

The map outlines are drawn as grey areas. To add the dotted connection lines you must add a point of type "map-connection" for each line, in the offseted scrap. It is also possible to draw "map-connection" lines directly in the scrap. The figures below show the xtherion interface and the resulting PDF.

Instead of below you can use above or none. With below the offseted map is drawn as a grey area in background. With above the offseted map is drawn in the main map as thin outline only. With none it is not drawn. You can change the colors with the layout option color preview-above and color preview-below. For example, to display the thin outlines red, use -layout-color preview-above [100 0 0]. This helps when the map gets messy.

Therion places the line points according to their distances from the station points in the scrap and to the 3D position of the stations (obtained from the centerline data).

It may happen that a vertical wall does not look really vertical in the outcome, because the sketch is not drawn well to scale, and therefore neither the scrap is so.

You can tell therion to draw a piece of a line vertically by adding the option "adjust vertical" (without the leading dash) to one, or more, of the line' points. Every point with this option is adjusted vertically with the previous point.

A similar problem can occur with horizontal surfaces, like the surface of a pond. Again, horizontality can be forced using the line point option "adjust horizontal".

The following figure shows a sample extended-elevation map with a vertical wall and a horizontal surface of a pond.

To draw a window in the wall in an extended section you draw the walls of the window passage with dashed lines, in the portion that overlaps with the section of the main passage.

In this example a pit has a window, and the contour of the window is drawn in the pit scrap with two lines of type "wall", one for the left side, the other for the right side (one line would have been enogth, but with two lines the scrap joins are easier). Both lines have the option "-outline in" so that the window would appear as a white hole in the pit map.

The contour of the window passage (in a second scrap) is broken at the intersection with the pit wall and the lines from the window to the wall have the option "-subtype presumed", so that they are rendered as dashed lines (this is not necessary: if the walls are not marked presumed, they are displayed in light grey, which is fine: it depends what you want to get). Furthermore the endpoints of these lines are use in the "join" of the scrap. To this extent it is necessary to insert line points in the pit wall (on the right in figure) at suitable positions.

Finally the window left wall must be replicated in this second scrap so that the bachground in the final map is properly colored, with a shaded area only where the window passages overlaps the pit wall.

The figure below displays the result. The xtherion sketch, on the left, has been colored for clearity. The "presumed" walls are shown in green; the left window wall is in red. The names of the stations are in red. The iblack numbers are the indices of the line-points of the right wall of the pit, used in the "join" commands. On the right is the result in the pdf document. You can see the dashed lines for the passage behind the pit and the shaded area.

The adjust command
Map preview command