Chapter 1: Unit system and the trench grid


In this lesson, we'll learn how to use the software AutoCAD to redraw an archaeological excavation plan. Here, we will talk about the unit system and create a 10x10 metre grid that can be printed out in a scale of 1:50, so as a 20x20 centimetre grid on actual paper.

First we need to make sure, that our software uses the metric system. For this, we can open a template of AutoCAD which you will find on the welcome page under the Start a new drawing (**Zeichnung starten**) box. If you open up the drop-down menu, you'll find a template called acadiso.dwt. Click on it and AutoCAD opens up a new empty drawing.

What you see now is the so-called Drawing Space (**Modell**), where we will do our drawing. In it, we will draw in 1:1, meaning that when we need a line that is 1 metre long, we will draw a line that is 1 metre long in the drawing space. Later, we can create so-called Layouts where we can specify what gets printed of the Drawing Space and at which scale. AutoCAD is working by default in millimetres, so to draw a line that is 1 metre long, we would need to draw 1000 units. We can change that if we want, but more on that later.


First, let's talk about scales. If you already know what a scale of 1:50 is, then you can skip this chapter and proceed to the next one. What does it mean to draw in 1:50? It basically means, that your drawing is 50 times smaller than the original. So a 50 centimetre line in the real world, would only be 1 centimetre on your drawing. On the other hand, if you would draw in 1:20, the 50 centimetre line would be 2.5 centimetres, so the final drawing would be bigger. If you would draw in 1:1, 50 centimetres in the real world, would be 50 centimetres on paper too.

It is obvious why we use scales, as trenches of 10 x 10 metres would not fit on regular drawing sheets. On an excavation, you do the drawing always to scale and a re-scaling of the drawing (for a publication for example) is always difficult. Not so much with a digital drawing, where we can effortlessly choose between different scales and produce results as much as we want.

Exercise: Draw a 10cm line

So lets do a little experiment. In the Drawing Space, we want to draw a 10cm straight line. To do this, we will select the Line (**Linie**) tool from the top menu and enter some coordinates by ourselves. Instead of clicking somewhere in the drawing, we will enter the coordinates in the Command Line (**Befehlszeile**) at the bottom, like this: 0,0,0 for the first point and then 100,0,0 for the second point. You can exit the Line tool by pressing Space (**Leertaste**). To see the line, you have to use the Mouse Wheel to zoom in and out and find the relatively small line at the world zero point. Zoom in on that, so you can see the line clearly.

What we did was draw a line 100 units to the right. When entering coordinates, we always enter X,Y,Z coordinates. As we are only drawing in the XY axis, the Z axis will always be 0. The first point was located at 0,0,0, which means, the line starts at the world zero point of the drawing. The second point had a X value of 100, which means we draw the line 100 units to the right.

When we switch over to the Layout view, we will see the line relatively big, as the default setting of ACAD needs some adjustments. First of all, we want to get rid of the grid that is showing as a background of the drawing. Double-click inside the drawing, so that the frame border becomes thick. Then press F7 to turn off the grid. After that, double-click outside of the drawing, so that the frame border becomes thin again. Then select the frame border by clicking on it, so it becomes blue and then right-click to open up the Properties. There, select the Ansichtsfenstermaßstab and turn it to 1:1. The line now is 10cm long, you can go ahead and print this page out to measure its dimensions.

Change the scale

So what we have learned from our little experiment is, that when drawing 100 units in the Drawing Space, we'll get a 10 cm line in the Layout when set to a scale of 1:1. We can simply remember therefore, that we will draw in millimetres when we are in the Drawing Space, because 100mm are equal to 10cm. As mentioned in the beginning however, a scale of 1:1 is not really practical, as we will redraw trenches that have dimensions of 10x10 metre. We therefore have to choose a smaller scale, in order to fit our redrawing to an A4 or A3 paper.

Let's say, that we want to have our layout in a 1:50 scale for a trench-by-trench view, and a scale of 1:100 for a more overview style layout. If we change to our Layout1 we can simply change the scale, as we already did before. We select the frame and right-click to open up the Properties. There, select the Ansichtsfenstermaßstab and turn it to 1:50. Immediately you'll see, that the line is now significantly smaller. You can print out the paper and measure the line, but we can also do some calculations.

We know that our line is 10 cm long in a scale of 1:1. If we change the scale to 1:50, the line should become a fiftieth of the original size, so it now should be 0,2 cm or 2 mm long. If you print out Layout1 you should see a 2 mm line. To keep things tidy, we should rename our Layout1 to something like Layout 1_50 (note that a colon does not work here), by right-clicking on the name of the tab at the button and hitting Rename (**Umbenennen**).

We can now repeat the process with Layout2 and remove the grid inside the frame (F7), change the scale to 1:100 in the Properties and renaming the layout to Layout 1_100. Naturally, the line should shrink to a size of 1mm.

Drawing an excavation grid

Of course, instead of a simple line, we want to create a redrawing of an archaeological trench. Before we start the redrawing of the excavation data however, we want to prepare firstly a grid in which we will do the redrawing. In our example, we will work with 10x10m trenches, which means that everything that we want to redraw will be inside that 10x10m border. In archaeology, there exist a lot of different systems, we basically only have to decide for one. In our case, we want to create a 10x10m border with some crosses. We want to create big crosses at the corners of the trench and smaller crosses in between along the border, each cross with a distance of 1m to the next one. The first thing we want to do, is to delete the line we just have drawn. Just select it with a click and press Del (**Entf**) to delete.

Setting up a new layer

Layers are used to separate different forms of content within a ACAD drawing. For example, we can assign different colours, line types or line thickness to different layers and use them therefore to differentiate between various stratigraphical units or in this case the trench border. In order to set up a new layer, we have to open the Layer Properties (**Layer-Eigenschaften**) in the top menu. A new window should appear.

So far, we only have one layer called 0, which is the standard layer of ACAD and can't be deleted. I usually don't end up using it. To create a new layer, press the New Layer (//Neuer Layer//) button at the top, indicated by a yellow star besides the layer symbol. Give the new layer a recognisable name like Excavation Grid. We also want to change the colour of the layer by clicking on the white colour box in the corresponding row. Pick a nice bright green colour. The last step is to make our new layer active, so that things we draw new will automatically be drawn to the new layer. Do you see the green check-mark besides the standard layer 0? That indicates, that 0 is the active layer. To change this to our new layer, simply double-click on its name Excavation Grid. Close the window by clicking on the little x in the top right or left corner.

Creating a cross in the right dimensions

So to start, we want to create a cross that we will use for the four corners of our grid. This cross should be 1cm high and wide in a scale of 1:50, so we have to think for a moment. If we want to draw a 1cm line in 1:50, how long should it be in 1:1? Of course it should be 50cm long, when we draw it. When printed on 1:50 scale, it should appear as 1cm. How long will it be on a 1:100 scale? You figure that out. So to draw this line, we will use exact coordinates in order to be very precise.

To start, we will select the Line tool (**Linie**) from the Start menu on top. Instead of drawing by hand, we will enter the coordinates in the Command Line (**Befehlszeile**) as we have done before. The first point should be 0,0,0 and the second point 500,0,0. To create a cross though, we also need a vertical line from top to bottom. Try to figure out the coordinates yourself before reading further.

To draw the vertical line, you should start at the point of 250,250,0 and end at the point of 250,-250,0. You now should have a perfect cross that should print out in the dimensions of 1 by 1cm. Let's now move the cross to the world zero point by selecting both lines first. Be sure you have selected both lines and then choose the tool Move (**Verschieben**) and make sure your Snapping is turned on. The corresponding symbol should be highlighted blue (see screenshot). If not, you can toggle Snapping on and off by hitting F3. With the Move tool selected and Snapping turned on, you can now snap into the centre of the cross by moving your mouse there. You should feel a snap towards the centre, which indicates that you can click (just once). You are now able to move your cross. Instead of clicking, we again enter the desired coordinates into the Command Line (**Befehlszeile**) -> 0,0,0. Your cross should now have moved to the world zero point.

The last step should be to copy the cross into the three remaining corners. Again select both lines and this time hit the Copy tool (**Kopieren**) and again click into the centre of the cross with Snapping turned on. Again we enter the destination coordinate by ourselves: 10000,0,0, 0,10000,0 and 10000,10000,0. You should now have a 10x10m grid on your drawing space.

More crosses...

So the last step for this lesson is to create smaller crosses to fill the gaps in between the bigger crosses that we just created. This time, the smaller cross should be 0,6cm high and wide in a scale of 1:50, so try to figure out for a moment how long we need to draw our lines in order to achieve this goal... 30 cm is the answer. So we repeat the steps we just did for a smaller cross. Let's start with the first point at 100,100,0 and the second point at 400,100,0. The second line starts at 250,250,0 and ends at 250,-50,0.

Now we need to position the smaller cross. Again, we utilise the method used before: Select both lines and select the Move (**Verschieben**) tool. Make sure Snapping is turned on and select the centre of the smaller cross. Now instead of clicking, we enter the coordinate that is exactly 1m to the right of our lower left corner. We enter the coordinates 1000,0,0 as the destination. This way we positioned the smaller cross exactly 1m to the right of our bigger cross. Now we could continue like this or we can utilise a small trick. Instead of entering the coordinate every time, we can save some time. First we select both lines of our smaller cross und then select the Copy (**Kopieren**) tool from the menu. First, ACAD wants to know the basis point. This time, instead of selecting the centre of our smaller cross, we want to select the centre of the cross to the left that is exactly 1m away. Make sure you have turned Snapping on. As you can already see, you can now make copies of the smaller cross 1m to the right of where your mouse is. Now click on the centre of the smaller cross that you want to copy itself. You have now created a second smaller cross 1m to the right of the first smaller cross. Now click on the centre of the newest small cross and you will create a third and so on... Continue until the lower line is complete, so you should have eight smaller crosses in between the two bigger corner crosses. Now we want to copy the whole lower row of smaller crosses to the top. Select them all (not the big ones!), select Copy (**Kopieren**) and as a base point the bigger cross on the left side. Copy the selection to the big cross on the upper left side and you should have the top row completed. For the vertical lines, you start again with one cross that you copy to the top of the lower left corner and then continue to the top. At last, you copy the left column of smaller crosses to the right side. Your excavation trench borders should now be ready.

There is only one thing to correct. If you have a look at your Layout 1_50 you'll notice, that we can't see the whole excavation trench on the A4 paper. As the extend on the paper is at 20cm, we come really close to the printable area of the paper. In order to see the drawing fully in a scale of 1:50, we need to change the paper size of Layout 1_50 from A4 to A3. To do so, do a right-click on the tab of Layout 1_50 and select the Seiteneinrichtungs-Manager. In the pop-up window, select Layout 1_50 and hit Change... (**Ändern...**). In the new window, select the drop-down at paper format (**Papierformat**) and select ISO A3 (297.00 x 420.00 mm). Hit OK and Close (**Schließen**). You now have to adapt the visible border by selecting it and dragging one corner to the extend of the paper. By double-clicking the border (border gets thick), you can edit the view inside with pressing and holding down the mouse-wheel. Drag the excavation trench to the centre of the paper and make sure, that you don't rotate the mouse-wheel, which would change the scaling. If you are happy, double-click outside of the border to make it not active, so you can go back to your drawing.

You can now proceed to Chapter 2: Referencing, Layers and Drawing

This page was last edited on 2024-04-11 14:13

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This page was last edited on 2024-04-11 14:13

Sebastian Hageneuer
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