# Digital Earth Reference Model

From Pyxis public wiki

Frequently abbreviated **DERM** a Digital Earth model uses a well defined discrete partitioning or grid of cells to model the Earth, as opposed to a continuous point based model developed for navigation of traditional geographic coordinate reference systems.

A Digital Earth Reference Model tends to encompasses four critical principals of a digital model namely:

**A discrete uniform partitioning**also called a Geodesic Discrete Global Grid System (a tessellation or tiling of cells over the Earth surface). Criteria for an optimized discrete global grid has been proposed by Michael Goodchild - generally,*equal area cells*that exhaustively cover the globe in closely packed hierarchical tessellations, each cell representing a homogeneous value:**A unique linear non floating point index**for each discrete cell that encompasses within the index both a parent child hierarchical relationship and a coordinate system that converges uniformly to the set of all real numbers;**A set of mathematical relationships and operations**built on the index: algebra, geometry, Boolean operations, image processing, etc; and- Drawing on signal processing theory,
**a strategy for quantizing values**(preferable integers) from analog or other digital sources to each discrete cell.

A DERM is designed to work in a digital environment providing statistically valid sampling, rapid storage, processing, transmission, discovery, visualization, integration, aggregation, and transformations. See: **DERM in action**.