[3D GIS]
A data structure associated with a terrain dataset used to define a multi-resolution surface, which organizes data into different levels of detail, or pyramid levels, and serves to improve performance by enabling the terrain to access only the data required for a particular display or analysis function. Data that is over-sampled or redundant can be avoided.Two pyramid types can be used to build a terrain: z-tolerance and window size. Z-tolerance pyramids filter data into different pyramid levels based on their vertical significance. Window size pyramids filter the data through localized selection biased to max, min, or mean height.