"Prim" is the term used for an object made from primitive shapes, such as cubes, spheres and other basic shapes. The prim modeling system is currently used by Second Life and has been in use since its inception. Shape is controlled by the basic position rotation and scale along with a set number of variables that transform the shape in a predetermined way, such as tapering, sheering and twisting. All items built in Second Life are built out of multiple prims grouped together to create an object.

The prim system is built for speed and ease of use and does a great job of making content creation more accessible for users. Building objects with this method is similar in concept to using building blocks stacked together to create something. With its ease of use, prims can help novice users get started on the road to further creativity and immersion in 3D modeling and virtual worlds.

The drawbacks to using prims becomes apparent when you have experience with a polygon based modeling system used by programs such as Maya, 3Dstudio Max, Cinema 4D and many others. In this system, rather than being made of primitive shapes, all objects are made of individual vertices and polygons which form a whole object. When editing shapes, you have control of each individual vertex allowing total power over the mesh. There are countless tools, deformers and operations you can use to help edit objects; therefore, there is nothing that can be done with the prim interface that can't be done in an external 3D application.

The downside to using an external 3D application is the same as the strong suit of prim based modeling, accessibility. The skilled use of the application takes time and training to utilize. The common user will be unable to contribute or participate in content creation leaving them as solely a consumer of the content. At the same time the applications used for this content are external from the virtual world requiring export, which means the objects are often created out of context from their final surroundings.

Organic shapes are much more difficult to create when building with a prim modeling system versus a polygon modeling system. To create an organic shape within a prim modeling system, you must group together multiple prims to create a curved surface. Without the direct control of vertices, your organic shapes tend to look lumpy and undefined with a prim based model.

It is important to note "prims" are made of polygons like any real time 3D object, but it’s the interface of how these objects are created which differs. It is not an obstacle to have both systems implemented into the same environment. In the end, both systems have a place in virtual worlds. If you need an e-learning or training space, it makes sense to have the content prebuilt in a 3D application to allow the highest visual quality and network stability with a static scene. However, if you want a community and entertainment space, it would be a great loss to take away the creative freedom of simple prim object creation. Prims have allowed Second Life to grow over the years and become the keystone virtual world of our time.

Stay tuned as mesh and collada will be discussed in a later post.

--Greg