Paper Cranes and Paper Planes
An Exposition on Unconventional 3D Modeling Technique
Making 3D graphics has never been easier — the technology is in full throttle and the community surrounding it is growing by the day. A quick search on YouTube reveals countless tutorials to model and animate everything from human faces to fauna. An even faster search on Google draws up innumerable blogs, forums, and galleries dedicated to the art of CGI. Yet it seems like the essence of creative modeling is lost in the throes of it all, to the point where all that matters is a passable end product.
A fun exercise is to make a paper crane. Conceptually, paper cranes are simple: elementary school students learn how to make them and can easily make tens of them in minutes. But structurally, these small folded creations are much more complex. Paper is flexible, mutable — hardly what you would want to imagine simulating in 3D modeling software. This falls under the idea of organic modeling, making meshes that look realistic on a material level. There are new products out there that are built for organic modeling, such as ZBrush. Of course, if it were that simple this article could end right here. But it’s not, unfortunately, because 3D modeling shouldn’t just be about finding the “tricks,” but also the exploration of the “how.”
Let’s go out on a limb and propose a new solution — how about modeling the paper crane exactly the way an elementary student would make one? The instructions seem simple enough:
We start with a simple plane, divided in half horizontally and diagonally, just as in the image above. We find that the process becomes quickly more complex — in order to adjust virtual “folds,” the mesh must be rescaled to act as paper would. Topology is important as it is easy to forget the original medium in the modeling process. It is because of this reason that materials such as paper are so difficult to model. Often called “cloth,” most materials like this are actually sculpted first and then assigned a “cloth” parameter, giving the mesh the properties of an elastically bound fluid. Since we’re using a procedural approach, however, we will end up taking more time at the expense of greater detail and attention to realism.
To make the folds, we select the appropriate vertex, such as a corner, which is where we would hold the paper if it were real. Good use of scaling, rotation, and translation makes the vertex move in the correct direction, making the fold. It is important to note during this process that the mesh will only fold up to the nearest edge. That is, edges in the model can be seen as the creases on which our paper folds. Take the image below, for example:
Notice how the flat surface has an edge diagonally. When the corner vertex is moved, the mesh folds along the edge:
It is this property that makes this method so difficult. Imagine needing to fold from that corner to the center of the square. The edge is in the way! In order to resolve this, we have to select all of the edges up until the center of the square, effectively preventing the other parts of the mesh from being affected.
While it would be nice to write every step to the process here, that would take far too long, so instead here is a nice timelapse of the creation process:
http://addisonleong.com/Images/Modeling%20a%20Paper%20Crane%20Small.mp4
Hopefully this has been an educational and fun post to read! A picture of the end result:
See you next time!
