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Drawing the plan outline for the Chamber

In this lesson we are going to create a new sketch file in our Therion project by importing our pocket topo plan drawing into the Therion editor, and linking it to our cave centre-line.

With the project files created in the previous lesson open in the XTherion application, we are now going to import the plan sketch from the files we exported from PocketTopo. Open the Map Editor (press F2 to switch to this view), and create a new file using the ‘File/New’ menu. Save this file in the project folder (which we called ‘Bull Pot’). The file type for sketches is .th2, so we will name this file ‘bpw.th2’.

Now from the ‘Edit’ menu, select ‘Insert Image’. In the dialog window which appears, change the ‘file types to show’ from ‘Pictures’ to ‘PocketTopo therion export’ in the list selector near the bottom right of the dialog box. Now navigate to the folder where we put our files exported from PocketTopo, select the ‘bpwth.txt’ file and click ‘Open’. You will be prompted to confirm some ‘XVI Properties’. Make sure that ‘Plan’ is selected because we want to import the plan sketch. Leave the scale (1:200), resolution (200dpi) and grid spacing (1.0m) settings at the default values as given here in brackets and click ‘OK’. You should now see the plan sketch drawing you did in PocketTopo displayed in the map editor.

Drawings in Therion are made up of parts called scraps. For very simple caves it may be possible to draw the entire plan survey in a single scrap, but in most cases more than one scrap will be needed. There are some basic rules to follow in deciding how to break a survey up into scraps.

  1. No scrap can overlap itself. So if your cave contains any passage which lies over or under another passage then you need to draw each of the overlapping passages in their own scrap.
  2. Scraps cannot be too big. How big is too big? Well you find out if you try to draw too much cave on one scrap because Therion will generate an error when you try to generate the survey. If this happens then you can always split the drawing up into more than one scrap at that point. So there is no need to worry about this problem now. Our survey for this tutorial will not get that big.
  3. For features such as colour by altitude, the entire scrap will be shaded the same colour, so it is a good idea to start a new scrap if there is a significant change in height in the part of the cave you are drawing. A good rule is to start a new scrap if the height has changed by over 5 metres from one part of your scrap to another. But use your judgement for what works best for your particular cave. Try to join scraps at places where there is no passage detail other than walls because Therion will do the best job then of creating a seamless join between them.

We start by creating a new scrap to draw the cave walls for the main chamber in our sketch. Down the right hand side of the map editor window are a number of panels with blue bars separating them. Scroll to the top of the screen and click on the ‘Objects’ panel heading to open that panel. At this stage if should just contain a single line of text saying ‘end of file’. This panel shows all the objects in our drawing, including scraps. So our first job is to create a new scrap. You can do this by clicking on the ‘Insert new scrap’ icon in the toolbar above this panel, or using the shortcut key combination ‘CTRL + r’.

The focus in the panels on the right should jump to the ‘Scraps’ panel when you create a scrap. Here we can give it an identifying name in the ‘id’ box. By default it will be named something like ‘scrap1’. It will really help later to use a system for naming scraps. We are drawing a plan in this scrap, so start the name with the name of the cave (or part of the cave for larger surveys). End the name with ‘S’ (for scrap) followed by ‘P’ (for plan), finishing with a number for this scrap. So we will name our first plan scrap for Bull Pot of the Witches ‘bpwSP1’. Finally we need to tell Therion what type of scrap this is. So select ‘plan’ in the ‘projection’ box below the ‘id’ field.

Before we start drawing, it will help to tell Therion what the scale of our sketch is. Therion can work this out for scraps which contain more than one survey station (because Therion knows how far apart the survey stations are). But when we come to draw cross-sections at stations there will only be one station in each scrap. So we will set the scale now. You will see the scale fields in the scrap information panel where we set the scrap id and type. The scale fields require a pair of points to be identified on the drawing, and the real world scale for these points to be entered below. You will see there is a button with the text ‘Scale’ on it on the scraps information panel. If you click on it then a red bar appears at the bottom of the window indicating we are in ‘scale scrap’ mode. We can now click in two places on the drawing to mark the start and end of the scaling arrow. Using the grid shown in blue on the screen, click on the bottom left corner of the grid, and then again on the point that is 10 square across and 10 squares up from the bottom left corner. You should now see a red arrow between these two points.

The picture scale points fields should now be showing numbers approximately from 0.0,0.0 to 395,395. Due to the fact we imported our drawing from PocketTopo we can actually work out the exact values that these fields should be set to. So set the values to 0,0 and 393.7,393.7 and click the ‘Update scrap’ button. The red arrow should now be perfectly aligned with the blue grid origin and the point 10m across and 10m up. So we also need to set the real scale points values to indicate the coordinates of these points in the real world. i.e. 0,0 10,10 with units set to ‘m’. Our completed scrap information box should look like the one shown above.

Next we need to mark the survey stations on our drawing. The Therion map editor gives us a helping hand here because our drawing was imported from PocketTopo. Switch to ‘insert point’ mode by clicking on the blue dot icon in the toolbar.

The mode status bar at the bottom of the screen should turn red and display ‘insert point’. Our survey stations are already indicated on the drawing as black dots. Click on one of these. It should turn blue and in the points info box on the right you should see a survey station point has been created automatically and given the station name from our PocketTopo survey. We are still in insert point mode, so click on the remaining survey stations along the main survey legs along the chamber. Do not include the stations on cross sections or on the side passage coming up from below. We will be drawing these in later scraps. The stations we want to include in this first scrap are 1.2, 1.3, 1.4, 1.6, 1.7 and 1.8 only. Remember if you do anything you did not want to then you can step back through your actions by selecting ‘Edit/Undo’ from the menu, or press Ctrl+z to undo. Once we have finished inserting points, exit the insert mode by pressing the ‘Esc’ key. The mode status bar should turn green again.

Now we can start to draw the walls. We do this using lines. In Therion a wall line has an inside and an outside, indicated with a small yellow tick mark on one end of the line. The ticks should all point into the ‘open air’ inside the cave passage, not into the solid rock. If a line is drawn the wrong way around then we can reverse it to put the tick on the correct side. But we can avoid having to do this for all our lines by drawing around the chamber in an anti-clockwise direction. Switch to ‘insert line’ mode by clicking on the ‘Insert new line’ button on the toolbar.

The mode status bar should turn red and display the message ‘insert line point’.

Drawing lines in the Therion map editor takes a bit of practise. Each line consists of a series of points, and each point has a pair of control points attached to it to control the curve of the line between the points. Click and hold down the mouse button at the point where you want to start drawing a new line, then while holding the mouse button down, drag the mouse in the direction you want to the line to head. This will drag out the control points from the point itself. Release the mouse button and click where you want to place the next point defining the line. Again drag the mouse while holding the button down. You should start to see how the position of the control points determines how the line curves between the points. Repeat this process until the entire line is defined. Then press the ‘Esc’ key to exit ‘insert line point’ mode. You can now select your line with the mouse and edit it. Click on any point and drag to reposition that point. The control points will appear for any selected point, and you can then click on these to move them. This method of drawing smooth curved lines enables fine control of the line appearance. Practise drawing some lines and editing them. Remember you can undo any step by pressing ‘Ctrl+z’. Or you can select an entire line and delete it by pressing ‘Ctrl+d’.

Once you have got a feel for drawing lines, we can draw our first wall. Going anti-clockwise around the outside of our drawing, we are going to draw the walls using smooth curved lines. Starting at the bottom right and going up the right side of our PocketTopo sketch, place line points to draw a smooth curved line matching the line of the wall. When you get to the top of the sketch where there is an open on-going passage we need to start a new line. So end the line by pressing the ‘Esc’ key. Your drawing should look something like this.

The Therion map editor draws all line types with the same appearance, so we need to check that the line type we have drawn is a wall line. Make sure your line is selected, then check the ‘Lines’ information panel on the right. If the type is not already set to wall then change it here now. All new lines drawn will be of the type you last selected here. Continue to draw the walls. You can start each new line by pressing ‘Ctrl+l’. This puts the map editor into ‘insert line’ mode, or ends a line if already in ‘insert line’ mode and keeps in that mode ready to draw another. When you get back to the start, exit ‘insert line’ mode by pressing the ‘Esc’ key to end the last line. Don’t forget to click ‘Save’ when you are finished drawing.

That completes drawing the walls for this lesson. If you are unsure how the sketch should look at this stage then find the bpw.th2 file in the Lesson 3 folder and open that in the Therion map editor to see what our drawing should look like. The final part of this lesson is about generating a survey from our drawing.

Back in the text editor (press F1) we need to include our drawing in our project. We do this by adding a line just below the ‘survey ...’ line at the top of the .th text file to include our .th2 file. The start of our project file should look like this:

  survey bpw

input bpw.th2

Now that we have included our drawing file, we can define a map containing the scraps in this drawing. We only have one scrap at the moment, so our map will just contain the one scrap. We need to give the map a name. As this is a plan map we are drawing, the convention we recommend is to name it after the cave, followed by ‘M’ for map, and ‘P’ for plan. So we are naming our map ‘bpwMP’ for this example. Inside the map definition we put the name of our scrap. So directly below the ‘input...’ line we add the following:

  map bpwMP

Finally we need to edit the configuration file to tell it to create some output for this map. Switch to the compile window (F3), and add the following line to the configuration file:

  export map -projection plan -o bpw.pdf

Here we are giving the instruction to create PDF document for our map. As we only have one map in the project we do not need to specify the name. We just indicate that it is a plan, and the filename we want to give the output file. Compile the project (press F9) and if everything has been done correctly then you should see the green ‘OK’ bar and find a file ‘bpw.pdf’ has been generated. Open this to view your Therion survey!

There is one more thing that has changed in our output now. The 3D model of the cave will now use the passage walls we have drawn to generate a better model. Open the bpw.lox file and take a look. Now instead of displaying thin cylinders along the survey legs, you should see a much better 3D representation of the cave passage we have drawn.