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Drawing symbols and other line types

In the last lesson we learned how to draw lines, and to check the line type. Now that our survey has the main walls drawn, we need to add some feature details. The Southerly part of our cave passage is a wide bedding plane at floor level, with a walking size section down the middle where there is a phreatic roof development. See the cross sections on the PocketTopo sketch. We can draw this step up in ceiling height using the ‘ceiling-step’ line type. Conveniently when we drew our walls we placed a point on the wall line exactly where this ceiling step feature joins the wall, so we can draw our line from this node. Start a new line, and click on the wall node where we want to start it. Draw the new line along the maroon line on the PocketTopo sketch as shown below. When the line is finished, set the type to ‘ceiling-step’ in the lines information panel.

Note the direction of the yellow tick at the start of the line. This indicates which side the marks along the line will be drawn when we render it. The UIS symbol for ceiling steps is a line with ticks pointing to the side of the line where the ceiling is lower, so our tick is pointing the right way. If it was not then we could reverse the direction of the line by ticking the ‘reverse’ checkbox in the lines information panel. Compile the project again and view the PDF. (Note that you have to close the PDF before you can recompile the project each time or you will get an error because the PDF file is locked by the PDF viewer). You should see the ceiling step line looking like this.

Once we have set a line type, any new lines we draw will be of the same type by default. So it makes sense to draw all the ceiling step lines together, before moving on to other line types. The line for the other side of our ceiling feature does not join the wall at a line point. There are two ways we can handle this. We could just draw our ceiling step line across the wall at the point we want it to join. Therion will not render the ceiling step line on the survey outside the boundaries of the wall by default. So the ceiling line will just stop at the wall even though we drew it crossing over beyond the wall. The alternative approach is to insert a new point into the wall line at the position where we want to end our ceiling step line. To insert a point, select the wall line, and then look in the lines information panel on the right. At the bottom there is an ‘edit line’ item. Click on this and a menu drops down. Select the ‘Insert point’ menu item and then click and drag at the position on the wall line where you want to insert the point. It is important to drag to pull out the curve control points. Otherwise the point will cause a sharp corner in the line. You can adjust the curve around the new point to make the wall line look right. Remember you can edit any point in a line by clicking on it to select it, and then drag it to a new position or adjust the control points to control the curve. If you mess it up, remember you can undo any number of steps by pressing Ctrl+z. Now we can draw the second ceiling step line.

Next we will look at the chimney dropping into our passage on the left hand wall. This poses some interesting problems which will teach us a number of useful things. Firstly, there is a wall line drawn through the middle of the feature. So we will need to break the line.

This is done by selecting the point on the line where we want to break it into two lines. Then from the ‘Edit line’ drop down menu in the line information panel, select ‘split line’. Now there are two lines meeting at the point in the middle of our feature. So select the point at the end of each of them in turn and then click and drag it to the edge of the feature. Adjust the control points on the end points and the next point along each line to get the curves aligned with the wall lines on the sketch. The tidied up wall lines should look like the image on the right (above).

Now we can draw the feature. Start a new line (Ctrl+l to put the editor into new line mode), then click and drag on one of the points at the end of the wall lines to start the new line from one of these wall end points. Draw around the chimney feature, making sure you also put a point on top of the other wall end line and continue to close the loop back on the starting point. The editor will automatically exit line drawing mode when you close the line into a loop. Set the line type to ‘floor step’ and compile the survey.

The images above show how our closed line looks, and how it was rendered in the PDF. There are two problems. The first is that the tick was pointing outside the loop in our case above. This means the floor step tick marks in the PDF appear outside the loop and not inside like we wanted. To fix this we simply need to reverse the line by ticking the ‘reverse’ check box in the line information panel. The other problem is that only half our floor step line was rendered. This is because the survey drawing is clipped by the outside of the wall lines. So only symbols and detail lines which are inside the boundary of our cave are rendered. Half our chimney is outside the boundary because Therion joins across gaps in the boundary wall lines with a straight line between the wall ends. This is straight through the middle of our chimney feature. We can turn off this clipping for our floor step line by adding the option ‘-clip off’ in the options field in the line information panel. Here is how it should all look when we have fixed these problems.

This has illustrated some useful lessons in line editing and clipping, but technically we have just drawn a pit in the floor and not a chimney going up. We could change the line type to ceiling step if this was an unexplored aven. But in this case we entered the cave down this chimney and there is a small passage coming in at the top of it. So we can actually redraw it properly to illustrate this. See if you can use what you have learned to make these edits yourself. Split the line forming the loop so we can set the line types separately for different parts and draw the side passage coming in to a floor step (a climb down) at the top of the chimney. Here is how it might look.

Some symbols are represented by points rather than lines. In the main part of our chamber we have some slope arrows and water flow symbols to draw. Switch to ‘insert point’ mode (Ctrl+p) and click on the top end of one of the slope arrows on the PocketTopo sketch. A new point should be created there. As we were last creating survey points the point type will probably be a new survey point. We can change the type in the Points information panel. The point type we need for a slope arrow is ‘gradient’. We also need to give our arrow a direction (they should point down the slope). This is done by ticking the ‘orientation’ checkbox in the information panel. You should see an arrow has been drawn on your new point. You can now click and drag on this arrow to rotate it around the point to orient it correctly to show the direction of the slope. The orientation arrow is only shown in the map editor while the point is selected. So as we add more slope arrows we should set the orientation of each one as we go or it is difficult to check they were all drawn correctly. As we are still in ‘insert point’ mode we can click on the other positions where we want slope arrows, adjusting the orientation of each one as we add them.

Water flow arrows work exactly the same way as slope arrows. Click on one of the water flow arrows on the PocketTopo sketch and change the point type to ‘water-flow’. Remember to tick the orientation checkbox again and set the direction of the arrow. Add a few water flow arrows to indicate where the stream flows down the chamber. Compile the project again and look at the PDF. Now it is beginning to look like a proper cave survey. There are plenty of point types and line types to explore in Therion. We can add some more to our survey later. But sometimes it is not practical to draw in every single rock or grain of sand. In the next lesson we will learn how to create areas and use symbol fills.