Digital Earth Reference Model
Encyclopedia
The term Digital Earth Reference Model (DERM) was coined by Tim Foresman in context with a vision for an all encompassing geospatial platform as an abstract for information flow in support of Al Gore’s vision for a Digital Earth
. The Digital Earth reference model seeks to facilitate and promote the use of georeferenced information from multiple sources over the Internet.
A digital Earth reference model defines a fixed global reference frame for the Earth using four principles of a digital system
, namely:
The distinction between "digital" versus "analog" Earth reference model is made in the manner the entire Earth surface is covered. Tessellation
refer to a finite number of objects/cells that cover the surface as discrete partitions while Lattice
refer to ordered sets of points that cover the surface in continuous vector space. The mathematical frame for a digital Earth reference model is a tessellation while the mathematical frame for an analog Earth reference is a lattice.
The value of a digital Earth reference model to encode information about the Earth is akin to the value obtained from other digital
technologies, namely synchronization of the physical domain with the information domain, such as in digital audio
and digital photography
. Efficiencies are found in data storage, processing, integration, discovery, transmission, visualization, aggregation, and analytical, fusion and modeling transforms. Data reference to a Digital Earth Reference Model (DERM) becomes ubiquitous
facilitating distributed spatial queries such as “What is here?” and “What has changed?”. Image
and signal processing
theory can be utilized to operate on data referenced to a DERM.
The DERM structure is data independent allowing for the general quantization of all georeferenced data sources onto the common grid. Application, algorithms and operations can then be developed on the grid independent of data sources.
Approaches using an analog reference require rigorous manual conflation
to satisfy the creation of digital products such as digital maps or other cartographic, navigation or geospatial information (see also GIS
). However, digital models are weaker at geometric transformations where translation, scaling and rotation must conform to the discrete cell locations wherein on an analog model with a continuum of locations geometric transformation are straight forward with no requirements for reprocessing or resampling.
A cell shape in such representations can be critical to the validity, adaptability and usefulness of the grid. As rectilinear structures are intuitive but lack optimization characteristics as a tessellation especially when tiled to a sphere, other schemes including voronoi regions, peano curves, triangles and hexagonal tilings have been advanced as superior alternatives.
Many ordering and naming models
have been implemented as geospatial database indexing for efficient data retrieval (R-Trees, QTM, HHC). Few of these models have encompassed a complete digital Earth reference model where both a formation of digits that represent a hierarchy where the index contains a parent child relationship and a formation of digits that monotonically converges by a set modulus to all vector Reals.
The International Society on Digital Earth has a standing committee considering DERM implementations and standards which includes both the Earth reference frame and the ancillary requirements for metadata and attribute semantics.
Digital Earth
Digital Earth is the name given to a concept by former US vice president Al Gore in 1998, describing a virtual representation of the Earth that is spatially referenced and interconnected with the world’s digital knowledge archives.-Original Vision:...
. The Digital Earth reference model seeks to facilitate and promote the use of georeferenced information from multiple sources over the Internet.
A digital Earth reference model defines a fixed global reference frame for the Earth using four principles of a digital system
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
, namely:
-
- Discrete partitioning using regular or irregular cell mesh, tiling or GridGrid (spatial index)In the context of a spatial index, a grid is a regular tessellation of a manifold or 2-D surface that divides it into a series of contiguous cells, which can then be assigned unique identifiers and used for spatial indexing purposes...
; - Data acquisition using signal processing theory (samplingSampling (signal processing)In signal processing, sampling is the reduction of a continuous signal to a discrete signal. A common example is the conversion of a sound wave to a sequence of samples ....
and quantizingQuantization (signal processing)Quantization, in mathematics and digital signal processing, is the process of mapping a large set of input values to a smaller set – such as rounding values to some unit of precision. A device or algorithmic function that performs quantization is called a quantizer. The error introduced by...
) for assigning binary values from continuousContinuum (theory)Continuum theories or models explain variation as involving a gradual quantitative transition without abrupt changes or discontinuities. It can be contrasted with 'categorical' models which propose qualitatively different states.-In physics:...
analogAnalog signalAn analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
or other digital sources to the discrete cell partitions; - An ordering or naming of cells that can provide both unique spatial indexing and geographic location addressGeographic coordinate systemA geographic coordinate system is a coordinate system that enables every location on the Earth to be specified by a set of numbers. The coordinates are often chosen such that one of the numbers represent vertical position, and two or three of the numbers represent horizontal position...
; - A set of mathematical operations built on the indexing for algebraic, geometric, Boolean and image processing transforms, etc.
- Discrete partitioning using regular or irregular cell mesh, tiling or Grid
The distinction between "digital" versus "analog" Earth reference model is made in the manner the entire Earth surface is covered. Tessellation
Tessellation
A tessellation or tiling of the plane is a pattern of plane figures that fills the plane with no overlaps and no gaps. One may also speak of tessellations of parts of the plane or of other surfaces. Generalizations to higher dimensions are also possible. Tessellations frequently appeared in the art...
refer to a finite number of objects/cells that cover the surface as discrete partitions while Lattice
Lattice (order)
In mathematics, a lattice is a partially ordered set in which any two elements have a unique supremum and an infimum . Lattices can also be characterized as algebraic structures satisfying certain axiomatic identities...
refer to ordered sets of points that cover the surface in continuous vector space. The mathematical frame for a digital Earth reference model is a tessellation while the mathematical frame for an analog Earth reference is a lattice.
The value of a digital Earth reference model to encode information about the Earth is akin to the value obtained from other digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
technologies, namely synchronization of the physical domain with the information domain, such as in digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
and digital photography
Digital photography
Digital photography is a form of photography that uses an array of light sensitive sensors to capture the image focused by the lens, as opposed to an exposure on light sensitive film...
. Efficiencies are found in data storage, processing, integration, discovery, transmission, visualization, aggregation, and analytical, fusion and modeling transforms. Data reference to a Digital Earth Reference Model (DERM) becomes ubiquitous
Ubiquity
Ubiquity is a synonym for omnipresence, the property of being present everywhere.Ubiquity may also refer to:* Ubiquity , a simple graphical installer made for the Ubuntu operating system* Ubiquity Records, an American music label...
facilitating distributed spatial queries such as “What is here?” and “What has changed?”. Image
Image processing
In electrical engineering and computer science, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame; the output of image processing may be either an image or, a set of characteristics or parameters related to the image...
and signal processing
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
theory can be utilized to operate on data referenced to a DERM.
The DERM structure is data independent allowing for the general quantization of all georeferenced data sources onto the common grid. Application, algorithms and operations can then be developed on the grid independent of data sources.
Approaches using an analog reference require rigorous manual conflation
Conflation
Conflation occurs when the identities of two or more individuals, concepts, or places, sharing some characteristics of one another, become confused until there seems to be only a single identity — the differences appear to become lost...
to satisfy the creation of digital products such as digital maps or other cartographic, navigation or geospatial information (see also GIS
Geographic Information System
A geographic information system, geographical information science, or geospatial information studies is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data...
). However, digital models are weaker at geometric transformations where translation, scaling and rotation must conform to the discrete cell locations wherein on an analog model with a continuum of locations geometric transformation are straight forward with no requirements for reprocessing or resampling.
A cell shape in such representations can be critical to the validity, adaptability and usefulness of the grid. As rectilinear structures are intuitive but lack optimization characteristics as a tessellation especially when tiled to a sphere, other schemes including voronoi regions, peano curves, triangles and hexagonal tilings have been advanced as superior alternatives.
Many ordering and naming models
Grid (spatial index)
In the context of a spatial index, a grid is a regular tessellation of a manifold or 2-D surface that divides it into a series of contiguous cells, which can then be assigned unique identifiers and used for spatial indexing purposes...
have been implemented as geospatial database indexing for efficient data retrieval (R-Trees, QTM, HHC). Few of these models have encompassed a complete digital Earth reference model where both a formation of digits that represent a hierarchy where the index contains a parent child relationship and a formation of digits that monotonically converges by a set modulus to all vector Reals.
The International Society on Digital Earth has a standing committee considering DERM implementations and standards which includes both the Earth reference frame and the ancillary requirements for metadata and attribute semantics.