Exercise 2: Modelling the Crepidoma

This will be the second exercise of building a temple to get a full reconstruction at the end and learn our tools in the process. You should have already completed Exercise 1: Modelling a Doric Column. Although we don't need the column in this exercise, we will need the knowledge from the last exercise, which will not be explained again. We will combine the result of that exercise with the column later. This chapter deals with the creation of the Crepidoma. You will find a written text below or, if you prefer to watch a video, here. Both methods cover exactly the same topics, so choose what suits you best. To start the project, please download this Cinema4D package and unzip it into a folder of your choice. It is important that you extract the ZIP archive somewhere, not just open it and navigate inside the ZIP. If you do not extract the ZIP, you will not find the attached background images.

Cite this video as: Hageneuer, S.: Teaching Archaeoinfomatics! - 3D Reconstruction - Exercise 2 - The Crepidoma. 2020. https://doi.org/10.5446/67631.

Creating the Crepidoma: two ways

The base (also called Crepidoma) is literally the first step into the temple. When you open the Cinema4D file you won't see anything. If you press F5 to see all the viewports, two of them should have background images visible. Now we need to think about how we are going to reconstruct the base of the temple, the ground on which our columns will stand. Of course there are many different ways to do this, but today we will learn two different ways: Spline Modelling and Box Modelling. Both ways lead to the same result, but I urge you to try both ways so that you can compare the different approaches to the same modelling problem. Later you will have to decide for yourself which way is better, or in other words, which modelling method you prefer.

Spline Modelling

In this type of modelling we use splines and generators to achieve our goal. The advantage of spline modelling is a kind of flexibility in its interpretation. For example, if we are creating a staircase, it is relatively easy to round the edges or add more subdivisions. Spline modelling is also good for computer performance. You will already be familiar with spline modelling as we used this technique in our first exercise Creating a Doric Column. There we used the Loft Nurbs and the Lathe Nurbs. Today we'll also be using the Loft Nurbs generator.

To start, we create a spline of the outer shape of the bottom step. We switch to our top view (F2) and select the pen tool from our spline menu at the top (see screenshot). We need to click on the four corners of our plan and then again on the first point created to close the spline. Take a closer look at the screenshot, which shows the finished spline (in red) and the location of the pen tool in the tool menu at the top. The next step should be to create a surface defined by the edges of the spline. We can do this in many ways, but for our purposes we'll need the Loft Nurbs generator, which can be found in the generator menu at the top (click and hold until the sub-menu opens). You can also find it in the Create/Generators/Loft menu.

In order for the generator to work, we need to tell it to use our newly created spline. To do this, we simply need to make the spline a child of the Loft Nurbs generator. This means that we need to click and drag the Spline into the Generator to make it a child of it. As you can see, the spline we created should now be filled with a surface. A small problem now is that we can't see the plan anymore. We can fix this by selecting the parent object Loft and in the Attributes Manager select the Basic tab and check the box next to X-Ray. This way we can see through the object and continue our work. Now we need to think about our next step. To do this we need to understand how the Loft Nurbs generator works. Basically it connects splines. So, for example, if you have a series of different splines next to each other, a Loft Nurbs can connect them into a solid 3D object. The shape of the splines doesn't have to be the same. The generator will interpolate the points between them.

We now need to create all the "folds" of this staircase, which means we need to place a spline wherever we want the 3D object to change direction or size. The first step would be to create the first step of this staircase. To do this, we simply need to tell the Loft Nurbs where the outer shape of this stair would end. As we now only have a flat surface that represents the base of the stair, we need to place another spline with the same dimensions a little higher than the base. You'll get it once we've done that. Copy the existing spline in the Loft Nurbs generator by selecting it and then pressing CTRL+C and CTRL+V. A second spline should appear at the top of your Object Manager. Drag and drop this into the Loft Nurbs, making sure it is on top of the existing spline (see screenshot).

The next step is to raise the newly created spline to the correct height. To do this, go to the front view by pressing F4 and make sure you have selected the new upper spline in the loft nurbs. Use your move tool E to move it up as you can see on the projected plan in the background. Also make sure you are not in Point/Edge/or Polygon mode, but in Object mode on the left. For this first step you only need to raise the spline a little. Do you see the 3D object? You have created your first step, well done! Now we need to create the second step. To do this, we will sort of repeat the steps from before. First we will build the base of the second step and then copy that base to move it up. Sounds simple enough, but how do you do it?

To create the base for the second step, we again need to copy the top spline and place it at the top of the Loft Nurbs list. So copy & paste the top spline (because it already has the correct height) and go to top view F2 to adjust the dimensions. Use the Scale tool T to do this. At the moment the copied spline has the same dimensions as the first stair, but we actually need to scale it down according to our plan. If you zoom into one of the corners you can see the scaling better. As we are scaling proportionally and the structure of the staircase is not proportional, you should be able to see that we can either make the horizontal or vertical dimensions fit. If you choose the side dimensions, we still have to compensate for the top and bottom dimensions. We will still use the scale tool but we will switch off the axis directions, we do not need them. In this case, I unchecked X and Y to scale only in the Z direction. This way I can scale the third spline to the correct dimensions.

Then we repeat all the steps from before:

• Copy the top spline and place it at the top of the Loft Nurbs.
• Adjust the height in the front view F4.
• Copy the top spline and place it on top of the Loft Nurbs.
• Adjust the dimensions for the next step in the top view F2.
• repeat In the end you should have 8 splines when you reach the bottom of the columns and when you switch to perspective view F1 you should see a 3D object that looks like a staircase. In the default settings we still need to adjust one option of the Loft Nurbs generator. When you select it, go to the Object Tab in the Attributes Manager and find the Linear Interpolation option. Make sure it is checked.

Box Modelling

This method is called box modelling because we start with a simple shape (usually a box or cube) and work from there. In the case of our staircase, box modelling is actually the easier way to create, but it is important to know that you have many options and in some circumstances spline modelling may be the better choice. If you have already created the staircase using spline modelling, you can make the model invisible to give you more room to work. To do this, select the Loft Nurbs generator in the Object Manager and click twice on the two small dots you see to the left of the green hook, so that both dots turn red. You should no longer see your spline model.

We start with a cube, which you can create by clicking on the cube button in the top row of tools or by navigating in the menu Create/Object/Cube. In the top view F2 we try to adjust the dimensions of our cube with the little golden handles. It also helps to make the cube transparent by checking the X-Ray option in the Basic tab of the Attributes Manager. Don't be too precise, as we're going to convert the cube into a mesh and then move the points around individually. To do this, press the C button (Make Editable) and our primitive object will be converted to a mesh. We can now switch to point mode by clicking on the points button on the left toolbar. Note that we're no longer working with a primitive, which gives us more options for manipulating the geometry.

We now need to match the corners of our cube to the corners of our plan, but we need to be aware that we are dealing with a 3D object. Each point that we see here in top view is actually two points on top of each other. When we move the corners we need to make sure that we move both points. To do this, we will use the Rectangle Selection tool by clicking and holding the Live Selection tool on the top toolbar until a submenu appears. There we'll find the Rectangle Selection. If we now click and drag a rectangle around the two points of a corner, we can be sure that we are selecting the two points above the corner. You can achieve the same result with the Live Selection tool, but we will leave it at that for now.

We can now move the two selected points to the corner of the plan and repeat this step for all four corners, so that in the top view our cube fits the outer shape of the staircase perfectly. However, if we look at our Front View (F4), we can see that the height does not fit at all. Using the same technique, we can move the bottom up and the top down, so we have our first step. Make sure that this time you do not select individual corners, but all the top points or all the bottom points with the rectangle selection. Switch to the perspective view F1. As you can see, we have created a first step, although it is quite small. The next steps will be more visible. You can already see the difference between spline and box modelling.

We now need to define the dimensions of the next step, as we did in Spline Modelling. There we created a new spline with the new dimensions. This time we will do it a little differently. To create the dimensions of the next step, we need to create a smaller polygon inside the upper polygon of our first step. To do this we need to switch to polygon mode and select the top polygon with our live selection tool. Now we can use the Inner Extrude command by pressing the i key. If you now click somewhere in the viewport and drag the mouse (without releasing the mouse button), you'll see the newly created polygon. Try to make it a little smaller than the original polygon.

To get the dimensions right, switch to top view F2 and use the scale tool again to scale your still selected polygon to the correct dimensions. You may have some problems with the direction of the polygon. If you look at the centre of the selected polygon, you'll see that the vertical direction is now Y, so if you want to scale in the vertical direction, make sure you leave the Y direction on in the Heading menu. If this change in direction confuses you, there is a trick you can use. Instead of using the object axis to scale, you can also use the world axis to scale. This is what the fourth icon in the heading menu is for (→ X Y Z coordinate system). When you click on the fourth icon (or press W) it changes from a cube and axis to a world and axis. If you now look at the axis of the selected polygon, you'll see that it now corresponds to the world system, and if you scale the polygon, you can use the X and Z axis. Be sure to change the coordinate system back to object coordinate system (axis and cube).

In any case, we now need to extrude the selected polygon upwards so that we can proceed to the next step. To do this, go to the front view F4 and use the extrude tool by pressing D. If you now click and drag the mouse, you'll see the next step appear. Try to get the height right, so raise the step to the appropriate height on the plan. If you miss it, don't worry, but don't use the Extrude tool again, as this will create extra unnecessary polygons. If you want to correct the height of the step, simply use the Move tool to move it up or down, as you still have the top polygon selected. Once you have done this, all you need to do is repeat the above steps for each step. When you're finished, the result should look something like this.

To conclude this chapter, I would like to leave you with one more thing. A very important part of 3D modelling is naming and organising your structures. As this project is quite simple at the moment, we don't need to do much sorting. Naming, on the other hand, is something you can do right from the start. I would suggest that you rename your loft nurbs to CrepidomaLoft and your cube object to CrepidomaBox. You can rename objects by double-clicking on them in the Object Manager. Save your progress and keep your file as we will be working on this in later chapters.