Particles are an important part of effects work, because they allow free-form information in 3D space. Unfortunately, there is no standard format for particles akin to Wavefront .obj. Most animation systems have their own proprietary particle formats. For example Maya uses the binary and ascii particle database formats .pdb and .pda file formats. Houdini uses the .geo and .bgeo geometry uber formats. Renderers typically have their own point cloud format such as RenderMan's PTC format and Houdini's .pc. All of these formats share a common theme. They allow particles to be iterated or indexed and associate a customizable set of attributes with them. The goal of Partio is to provide a unified interface akin to unified image libraries that makes it easier to load, save, and manipulate particle files.
At Walt Disney Animation Studios, we had used a mix of PDB formats, PTC formats and BGEO formats, depending on the authoring environments. Many of our tools supported more than one of these, but the code was scattered and copied to read these formats. Additionally, some of these formats required linking to large libraries to use. For this reason we desired a library that could read and write all of these file formats in a simple way. This would allow all of our tools to easily support all the possible formats that we could throw at them. It also allowed more flexibility in moving particles into proprietary packages without having to write an importer/exporter for every different tool.
A goal we have is to have an efficient cached and ordered format that allows nearest neighbor searches without an initial KD-Tree search and also can have only part of the particle set in memory at once. In our initial version of Partio, we have not created that format, because we would instead like to collaborate to design the appropriate format in the context of open source.