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3.2 Areas
Now that you have completely enclosed the cave passages with cave walls
and invisible lines, you can see them greyed out, so the passages
are readily visible on the image.
Tunnel recognizes areas: each sequence of connected paths that form a closed
loop defines an area. The sequence of paths is the contour of the area.
Areas are not saved with the data, they must be recalculated
when you load the sketch from the xml file, or when you make changes to the
drwaing. To recompute and
display the areas click on the button "Update Areas" (or the menu
"Update | Update areas"). The picture below shows the sketch with the areas
lightly greyed.

Clicking on the "Update Areas" button you effectively invoke the
areas calculation algorithm. This algorithm is rather simple and you should
understand it in order to work effectively with areas.
Now I report the algorithm as explained by J. Todd:
The algorithm to generate the areas is simple: Follow a path till it hits
the first node. If there are other paths that connect to that node, choose
the first path on the left (clockwise), and follow it until you reach
another node. If there are no paths connecting to that node, go back on
the same path in the opposite direction. Repeat until you reach the
starting path, going in the same direction. This series of paths defines one
area. Continue until all areas are accounted for.
This algorithm explains why it is crucial that paths must be connected
correctly to one onother.
Also remember that the centerline and connective paths of paths are not used
by the areas calculation algorithm.
You can also display the areas hatched (as well as greyed).
This way it is easier to distinguish them from one another.
This feature will come useful when we draw more complicated
caves. For the moment just play with it.
Click on the menu "Import | Striped areas".
The picture below shows the sketch displayed with hatched areas.

marco corvi - Wed May 10 10:58:55 2006
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