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Adding fill areas

Some survey symbols fill an area rather than appear at a single point. In this lesson we will create some areas with symbol fills. Typical area symbols show detail of what is on the floor. e.g. Water, mud, sand, debris and boulders. Our main chamber area has boulders all over the floor, so rather than draw them all we will define the area we want them to cover and then assign a symbol to fill that area. An area consists of a series of lines defining the boundary of an enclosed area. These can be lines of the various different types which appear on the survey, or can be invisible lines defining the perimeter of the area without actually appearing on the finished drawing. Like other symbols, an area fill will be clipped by the cave walls in the scrap. So you can just draw an area over the top of the passage, passing outside the walls. When the drawing is rendered only the parts of the area inside the walls will be filled with the area fill symbol.

We could join the lines defining the border of the area onto points on the wall lines, making the wall lines part of the area boundary. But this requires us to split the wall lines at the points where we want to join on the lines defining the other parts of the area boundary. It also makes it harder to spot that there is an area fill defined because the area boundary is less obvious in the scrap when viewed in the map editor. Here is an example showing three ways we could define an area. On the left we have split the wall lines at points and then started and ended two new border lines at these points on the walls. In the middle we have drawn two lines crossing over the walls to define part of the passage as an area. Note that the wall lines are included in the set of lines defining the area. On the right we have drawn just a single line in a loop across the passage to define the section of passage inside the loop as an area. All the lines defining the area are coloured red here in each case.

All these cases would render the same because Therion will only draw symbols inside the passage walls. But it is strongly recommended to use the third of the three methods shown. This is because lines defining an area all get assigned unique id codes, and if you later split any of the lines the area is very likely to get broken as the id codes do not get copied onto both segments of the line. So to avoid risk of messing up the areas later we should as a rule avoid using lines which are serving another purpose in the sketch (like the walls) in our area definition. It is safer to draw the area with a single line, so this is what we will do here.

We will draw the line more carefully than in the rough illustrations above, so that it properly marks out the parts of our passage where the floor is covered with boulders. Once the line has been drawn, set the line type to ‘border’ to indicate that the line is just a border between different areas of the cave. Next click the ‘new area’ toolbar button (or press Ctrl+a).

The map editor should now be in ‘insert area border’ mode as shown by the text in the red status bar. We define the area by clicking on each line which surrounds the area in turn, working around the area either clockwise or anti-clockwise. In our simple case here we only have one line to click on. You should see the line id being added to the ‘Areas’ information panel (identified by long id codes in a text box, with ‘end of area’ at the end of the list).When the line has been added to the area, press the ‘Esc’ key to exit ‘insert’ mode. You can change the area fill type in the ‘Areas’ information panel. Set it to ‘blocks’. Compile the project and check the rendered drawing. The area should be filled with blocks, but the border line is also drawn as a solid thin black line where it crosses the passage. We want to hide our border line, so select it and enter ‘-visibility off’ into the ‘options’ field in the ‘Lines’ information panel. Now when you render the drawing the border lines should not appear.

Sometimes it is not possible to draw an area border with a single line. When two areas sit side by side they need a border line in common. This is because it is only passage walls which clip a symbol fill. So if we drew two overlapping circles then each would display their symbol fill in the part of the areas which overlap, as shown here.

Instead we need to draw an area joined onto the line of another. In our example we will draw a pool in the passage at the bottom right of our sketch, and a mud/clay floor in the main passage at this end of the cave. When we add the areas in this case we need to add all the lines which make up the area. Be careful to only click on each line once so that the id is only added once in the ‘Areas’ information panel. If you added one twice by mistake you can delete it by clicking on the id, and then using the ‘Delete’ button in the information panel. If there are more than three lines making up the boundary of an area then you must add them in order going around the boundary.

Here is how our new areas look in the map editor and the rendered drawing. Note that we have made the line bordering the pool visible, but hidden the line bordering only the mud area.