A Global Grid System is an Earth Reference System based on a hierarchy of area tessellations (i.e., grid cells) that partition and address the entire globe. There is an OGC DGGS standard that goes further and defines a Discrete Global Grid Systems (DGGS) as an Earth Reference System based on a hierarchy of equal area tessellations.
A DGGS is a form of Earth reference that, unlike its established counterpart the coordinate reference system that represents the Earth as a continual lattice of points, represents the Earth with a tessellation of nested cells [Clark, 2000]. Generally, a DGGS will exhaustively partition the globe in closely packed hierarchical tessellations, each cell representing a homogeneous value, with a unique identifier or indexing that allows for linear ordering, parent-child operations, and nearest neighbour algebraic operations.
Advantages of Global Grid System
Real-time spatial/temporal big data management that enables state of the art storing, accessing and processing of global spatial/temporal data
Solves the problem of integrating location data from multiple sources with an efficient global representation of the earth that facilitates analysis and rapid integration of large datasets
Data organized with clear relationships to each other facilitating parallel and distributed processing
Global seamless integration of heterogeneous datasets
Real-time data integration with less human intervention, paving the way for 'linked data' and AI-based analysis
DGGS Evaluation
The investigation into DGGS included several existing systems:
Google's S2 geometry is a hierarchical decomposition of the sphere. Google's S2 geometry is a hierarchical decomposition of the sphere. S2 is a type of geo-hash but is it unique in that it uses a Hilbert space-filling curve, Java and C++ Libraries.
Hierarchical Triangular Mesh (HTM) Originally developed by SkyServer for the Sloan Digital Sky Survey (SDSS). Microsoft Research developed a C, C++, and Java library. The C++ library was adapted to work with SQL Server.
Geo-Hash index is a hierarchical spatial data structure that subdivides a sphere into grid like areas. The geo-hash system
http://geohash.org/ was invented by Gustavo Niemeyer. This system uses a Z-order curve to transform the two-dimensional spatial point (latitude, longitude) into a hash.
Hexagon – PYXIS hexagon is a commercial SDK and ISEA Aperture 3 Hexagon (ISEA3H) DGG. There are pre-generated ISEA grids available, Pre-Generated ISEA DGGs.
The rHEALPix DGGS - rectangular cells in equatorial regions [ <= +/- ~42o latitude] and a mix of rectangular and triangular cells in the polar regions.
Different DGGS have a subset of capabilities. These capabilities may not meet the requirements of the OCG DGGS standard but may be important to PB and our clients.
S2 Geometry library is a mature full feature library that is used by Google Maps, MongoDB, Foursquare, Amazon DynamoDB, Uber/Node.js, SafeSoftware, Areospike, and MapBox.
GeoHash is widely used in the industry, is recognizable by many and can be easily used without proprietary or complex software. PostGIS, ElasticSearch, the Geomesa opensource project, and many others support Geohash gridding in their systems.
PB is currently using Geohash for its Global Grid System. We have full support for polygon decomposition and coordinate conversion in our PB LI SDK.
Each Global Grid System is very different in the way it tessellates the globe. However, once data has been encoded into a (D)GGS indexing and query operations are similar to, or identical, from system to system. This makes it possible to architect an abstraction layer to isolate the dependencies on any one Grid System.
The OGC DGGS Standard is being currently being considered for adoption by ISO. The "equal area" OGC DGGS requirement addresses two key issues:
1. The repeatable representation of measurements – observations, interpretations, and events globally. As stated in the Discrete Global Grid Systems Abstract Specification "Equal area cells provide global grids with spatial units that (at multiple resolutions) have an equal probability of contributing to an analysis."
2. A uniform cell, equal area, facilitates interoperability between different DGGS [Amiri et. al. 2015]. It can enable a lossless data conversion from one DGGS index method to another.
As [Amiri et. al. 2015] state in their conclusion "data allocated to cells can be represented in different ways using different types of DGGS and that there exists a simple conversion between these representations that can be used to unify the data available given any DGGS."
IOT data may benefit from cells that have equal area.
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John Merola
Knowledge Community Shared Account
Shelton CT
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Original Message:
Sent: 05-14-2019 13:57
From: Dan Adams
Subject: Global Grid System Question
Hi Community--
I was just in a conversation with an exec at a company that is processing a large amount of IoT data. He asked if PB is using a Global Gridding systems, and, if so, which one we selected and why.
I know we are, but didn't feel comfortable enough with the details to give much of an answer.
Do any of the PB-ers have input?
It would be good to know what other organizations are doing with Global Grid technology too.
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Dan Adams
Pitney Bowes
White River Junction VT
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