Waterbomb/Preliminary Base
This tutorial will illustrate some of the ambiguity related to finding the correct collapsed base from a crease pattern (cp).
Here is our first crease pattern:
Normally this is all you can expect in a crease pattern, no crease directions, and no pictures of the base, only pictures of the finished model. Often this complicates things and forces the folder to try multiple times, guessing at directions of the creases. Now, lets see how we can collapse this base. Option 1 is as follows:
And option 2 is as follows:
After collapsing the two different options, you should see that option 1 gives you the preliminary base while option 2 gives you the waterbomb base. The astute person sees that the two options would be exactly the same if one were turned over. This similarity is represented in the folding by doing a maneuver I call after hearing it from someone else, "pushing the button". This is where when part of the paper is sticking up towards you, you push it down so it sticks down away from you. You can change the preliminary base into the waterbomb by "pushing the button" in the center of the paper. This maneuver is photographed following:
Since the crease pattern leaves this ambiguity, I often must try different combinations of having parts of the semi-collapsed base sticking up or sticking down, by pushing different buttons in different directions. This is often very annoying and time consuming, and makes me try other models when I get frustrated.
Now, you can also learn more from this tutorial. On this crease pattern, their are 5 main locations to take interest in. Each corner and the center of the paper. The center of the paper begins at 360 degrees, but, with 8 creases going through the node, we now know that the center of the paper is narrowed to 45 degrees. Also, each corner has one crease going through it, and since it started at 90 degrees, they are narrowed to 45 degrees also. I call these 5 points nodes, namely, they are locations where creases converge and narrow the paper. Often the nodes represent landmarks on the finished model, and matching up which node is which appendage on the final model helps tremendously in collapsing the base. Often, additional pictures of the crease pattern are provided, with this type of information provided. When you see circles or rounded shapes drawn in a different color around nodes, you know this represents an appendage, and the radius of the circle represents the length of the appendage. Often the nodes are also labeled with what part of the model they are. If this is provided, use it to help collapse the model, and determining the relative location of the nodes. All of this will be further demonstrated in the continued tutorials.
One last pattern to notice. Each node has alternating crease directions. Namely, on a node, the creases go mountain, valley, mountain, valley etc. or valley, mountain, valley, mountain etc. This pattern exists in about 85% of the instances, and when I am trying to determine direction of creases, I often assume that this will be the pattern.