Like in many things research is the first step when it comes to creating an animation. Many things need to be understood when attempting to animate a scene. This research can include many elements such as the anatomy of the creatures involved, the motions themselves as well as many other features. Once the animator believes they have done a sufficient amount of research and understand everything they need to, they can then move onto the planning stages.
When planning animation for any medium a lot of thought needs to be invested into the poses the characters will take and the progression of their motions. Its common practice for animators to perform the role themselves from many different angles to gain an understanding of the how the poses throughout the performances are constructed. From this reference footage the animator can then study the performance the do thumbnail drawings. Drawing out particular poses is a much faster and effective way to pose a character rather then posing them entirely within a 3D software like Maya. To do these drawings a certain amount of drawing ability is required to effectively communicate the poses and change across the movements.
Its quite common practice for animators to do thumbnail drawings while planning their animations. These thumbnail drawings are small and simple only displaying the necessary details to communicate the poses the animator wishes to create. However just because they are simple does not mean they do not require a certain amount of knowledge and practice to perform. For the drawings to do their job of helping the animator understand the details of the pose in its simplest form possible the drawings must be accurate. This requires knowledge of proportions and human anatomy as well as the ability to draw it.
From this point the animator translates the drawings onto a character in a 3D program, these then serve as the poses for the animation. They are adjusted in the 3D software to better suit what the animators require and then serve as the beginning as the blocking stage of animation.
The CGBros. (April 14, 2014). CGI Animation Breakdowns HD: Walt Disney’s “Frozen” Shot progression – by Bobby Pontillas [Video File]. Retrieved from https://www.youtube.com/watch?v=2z_k2z5m6H0