What are the pros and cons of using impostors and billboards versus other LOD methods?

1 What are impostors and billboards?

Impostors and billboards are both types of LOD models that replace the original geometry of an object with a flat image. An impostor is a textured quad that always faces the camera, while a billboard is a textured quad that is aligned with a fixed axis, such as the vertical or horizontal axis. Both techniques use pre-rendered images of the original object from different angles, and switch between them depending on the camera position and orientation.

2 How are impostors and billboards created?

To create impostors and billboards, you need to render the original object from multiple viewpoints, and store the images as textures. You can use a spherical or a cylindrical coordinate system to define the viewpoints, and use a script or a tool to automate the process. Then, you need to create a quad mesh for each object, and assign the appropriate texture to it. You also need to define a distance threshold or a screen size criterion to determine when to switch from the original object to the impostor or billboard.

3 What are the benefits of impostors and billboards?

Implementing impostors and billboards can offer several advantages for 3D graphics, such as reducing the number of polygons and draw calls, which can improve performance and frame rate. Additionally, these methods can save memory space by using less data than the original objects. Furthermore, impostors and billboards preserve the appearance and lighting of the original objects, as they use pre-rendered images that capture the details and shadows of the objects. Finally, they handle transparency and occlusion better than other LOD methods, as they do not have gaps or holes in their geometry.

4 What are the drawbacks of impostors and billboards?

When using impostors and billboards, there are some drawbacks to consider, such as increased texture memory usage and potential visual artifacts like aliasing or popping when the camera moves too quickly or too close. Additionally, impostors and billboards lack depth and parallax effects since they are flat and do not change shape or size with perspective. Moreover, they require more preprocessing time and storage space before rendering.

5 When to use impostors and billboards?

When deciding whether to use impostors or billboards, you need to consider your goals and constraints. Factors such as the complexity and size of the original objects, the type and movement of the camera, and the lighting and environment of the scene can all influence your decision. Generally, impostors and billboards work best for objects with a lot of polygons and details that are relatively small or distant from the camera, with static or slow-moving cameras, and in static or uniform lighting. However, they may not be suitable for fast or dynamic cameras that change position or orientation frequently, or for complex lighting that changes over time or with the camera angle.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?