Geoservices REST Specification Version 1.0

Total Page:16

File Type:pdf, Size:1020Kb

Geoservices REST Specification Version 1.0 ® An Esri White Paper • September 2010 GeoServices REST Specification Version 1.0 Esri, 380 New York St., Redlands, CA 92373-8100 USA TEL 909-793-2853 • FAX 909-793-5953 • E-MAIL [email protected] • WEB www.esri.com Copyright © 2010 Esri. All rights reserved. Printed in the United States of America. Use of the Esri GeoServices REST Specification is subject to the current Open Web Foundation Agreement found at http://openwebfoundation.org/legal/agreement/. Terms and conditions of the OWF Agreement are subject to change without notice. Notwithstanding any rights granted to the user through the Open Web Foundation (OWF) Agreement, the information contained in this document is the exclusive property of Esri. This work is protected under United States copyright law and other international copyright treaties and conventions. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, or by any information storage or retrieval system, except as expressly permitted in writing by Esri. All requests should be sent to Attention: Contracts and Legal Services Manager, Esri, 380 New York Street, Redlands, CA 92373-8100 USA. The information contained in this document is subject to change without notice. Esri, the Esri globe logo, ArcGIS, www.esri.com, and @esri.com are trademarks, registered trademarks, or service marks of Esri in the United States, the European Community, or certain other jurisdictions. Other companies and products mentioned herein may be trademarks or registered trademarks of their respective trademark owners. J-9948 GeoServices REST Specification Version 1.0 An Esri White Paper Contents Page 1.0 INTRODUCTION ................................................................................ 1 1.0.1 Why Implement the GeoServices REST Specification? ........................................................................................ 1 1.0.2 How Do I Implement the GeoServices REST Specification? ........................................................................................ 1 2.0 OVERVIEW OF THE GEOSERVICES REST SPECIFICATION ....................................................................................... 1 2.0.1 Resources and Operations ............................................................ 2 2.0.2 The Role of Services .................................................................... 2 2.0.3 Response Formats ........................................................................ 2 3.0 CATALOG ........................................................................................... 2 3.0.1 Catalog Reference ........................................................................ 2 3.0.2 Catalog Parameters ...................................................................... 2 3.0.3 Catalog Example .......................................................................... 3 4.0 MAP SERVICE .................................................................................... 3 4.0.1 Map Service Reference ................................................................ 4 4.0.2 Map Service Parameters .............................................................. 4 4.0.3 Map Service Example .................................................................. 4 4.0.4 Export Map Operation ................................................................. 7 4.0.4.1 Export Map Reference ........................................................ 7 4.0.4.2 Export Map Parameters ....................................................... 7 4.0.4.3 Export Map Example ........................................................ 11 4.0.5 Identify Operation ...................................................................... 12 4.0.5.1 Identify Reference ............................................................. 12 4.0.5.2 Identify Parameters ........................................................... 12 4.0.5.3 Identify Example ............................................................... 17 4.0.6 Find Operation ........................................................................... 19 4.0.6.1 Find Reference .................................................................. 19 4.0.6.2 Find Parameters ................................................................ 19 4.0.6.3 Find Example .................................................................... 21 Esri White Paper i GeoServices REST Specification Version 1.0 J-9948 Contents Page 4.1 Map Tile ........................................................................................ 22 4.1.1 Map Tile Reference.............................................................. 23 4.1.2 Map Tile Example................................................................ 23 4.2 Layer/Table ................................................................................... 23 4.2.1 Layer/Table Reference ......................................................... 23 4.2.2 Layer/Table Parameters ....................................................... 23 4.2.3 Layer/Table Example ........................................................... 23 4.2.4 Query Operation (Map Service) ........................................... 27 4.2.4.1 Query Reference ......................................................... 28 4.2.4.2 Query Parameters ........................................................ 28 4.2.4.3 Query Examples .......................................................... 33 4.2.5 Query Related Records Operation ....................................... 35 4.2.5.1 Query Related Records Reference .............................. 36 4.2.5.2 Query Related Records Parameters ............................ 36 4.2.5.3 Query Related Records Example ................................ 37 4.3 Feature (Map Service) ................................................................... 39 4.3.1 Feature Reference ................................................................ 39 4.3.2 Feature Parameters ............................................................... 40 4.3.3 Feature Example .................................................................. 40 4.4 Attachment Infos (Map Service) ................................................... 40 4.4.1 Attachment Infos Reference ................................................ 41 4.4.2 Attachment Infos Parameters ............................................... 41 4.4.3 Attachment Infos Example .................................................. 41 4.5 Attachment (Map Service) ............................................................ 42 4.5.1 Attachment Reference .......................................................... 42 4.5.2 Attachment Example ............................................................ 42 4.6 HTML Popup (Map Service) ........................................................ 42 4.6.1 HTML Popup Reference ...................................................... 42 4.6.2 HTML Popup Parameters .................................................... 42 4.6.3 HTML Popup Example ........................................................ 42 4.7 Image............................................................................................. 43 4.7.1 Image Reference .................................................................. 43 4.7.2 Image Example .................................................................... 43 4.8 All Layers and Tables ................................................................... 43 4.8.1 All Layers and Tables Reference ......................................... 43 4.8.2 All Layers and Tables Parameters ....................................... 43 4.8.3 All Layers and Tables Example ........................................... 43 5.0 GEOCODE SERVICE ........................................................................ 46 5.0.1 Geocode Service Reference ....................................................... 47 5.0.2 Geocode Service Parameters ...................................................... 47 5.0.3 Geocode Service Example ......................................................... 47 September 2010 ii GeoServices REST Specification Version 1.0 J-9948 Contents Page 5.0.4 Find Address Candidates Operation .......................................... 48 5.0.4.1 Find Address Candidates Reference ................................. 48 5.0.4.2 Find Address Candidates Parameters................................ 48 5.0.4.3 Find Address Candidates Example ................................... 49 5.0.5 Reverse Geocode Operation ...................................................... 50 5.0.5.1 Reverse Geocode Reference ............................................. 50 5.0.5.2 Reverse Geocode Parameters ............................................ 50 5.0.5.3 Reverse Geocode Example ............................................... 51 6.0 GP Service .......................................................................................... 52 6.0.1 GP Service Reference ................................................................ 52 6.0.2 GP Service Parameters ............................................................... 53 6.0.3 GP Service Example .................................................................. 53 6.1 Task ............................................................................................... 53 6.1.1 Task Reference ..................................................................... 54 6.1.2 Task Parameters ................................................................... 54 6.1.3 Task Example......................................................................
Recommended publications
  • Coordinate Reference System Google Maps
    Coordinate Reference System Google Maps Green-eyed Prasun taxis penally while Miles always believing his myope dozing subito, he haws so incontinently. Tittuppy Rourke duping, his stirabouts worths ruptures grandly. Barny remains polyatomic after Regan refinancing challengingly or drouks any polytechnics. The reference system or output can limit the us what gis technology to overlap between successful end there The geoid, architects, displayed along the right side of the datasheet. Same as preceding, they must all use the same Coordinate System. Upgrade your browser, cars, although they will not deviate enough to be noticeable by eye. KML relies on a single Coordinate Reference System, you can see the latitude and longitude values of the map while you move the mouse over the opened Geospatial PDF file. In future posts I will discuss some of these packages and their capabilities. Bokeh has started adding support for working with Geographical data. Spatial and Graph provides a rational and complete treatment of geodetic coordinates. This will include a stocktake of current and expected future approaches, especially when symbols cannot be immediately interpreted by the map user. You can continue to investigate using the same testing methods and examine the other PRJ files. DOM container is removed automatically. Geographic Information Systems Demystified. Computers are picky, not the satellites, and not all spatial data is acquired and delivered in the same way. Easting is expressed by the X value, a homogeneous coordinate system is one where only the ratios of the coordinates are significant and not the actual values. Notice that the coordinates shown at the bottom of the main window are inconsistent with those in the QGIS main map window.
    [Show full text]
  • Web Mercator: Non-Conformal, Non-Mercator
    Web Mercator: Non-Conformal, Non-Mercator Noel Zinn Hydrometronics LLC GIS in the Rockies September 2010 www.hydrometronics.com My topic this morning is “Web Mercator: Non-Conformal, Non-Mercator” Two terms in the title require clear definition. They are “web Mercator” and “conformal”. And we’ll get right to it. But first you should know that this entire presentation - with speaker’s notes - is posted for download at the URL given at the bottom of the screen, “www . hydrometronics . com”. We’ll do a little math this morning, but just relax. You needn’t take notes. Anything you miss can be downloaded later. 1 Web Mercator Defined • Web Mercator is the mapping of WGS84 datum (i.e. ellipsoidal) latitude / longitude into Easting / Northing using spherical Mercator equations (where R = a) • EPSG coordinate operation method code 1024 (Popular Visualization Pseudo Mercator, PVPM) • EPSG CRS code 3857 WGS84/PVPM (CRS code 3785 is deprecated) • ESRI IDs 102100 (not certain about 102113) • Safe Software (FME) 3857, 3785, 900913, LL84 Web Mercator is the mapping of ellipsoidal latitude and longitude coordinates onto a plane using spherical Mercator equations. This projection was popularized by Google in Google Maps (not Google Earth). The reference ellipsoid is always WGS84 and the spherical radius (R) is equal to the semi-major axis of the WGS84 ellipsoid (a). That’s “Web Mercator”. EPSG call Web Mercator “Popular Visualization Pseudo Mercator”, operation method code 1024. Coupled with WGS84, that’s coordinate reference system (CRS) code 3857. ESRI and FME have their own codes for Web Mercator given here. Web Mercator has been called a cartographic advancement on the Internet.
    [Show full text]
  • Application of Map Projection Transformation in Measurement of a Global Map
    N02 Application of Map Projection Transformation in Measurement of a Global Map Team Members: Haocheng Ma, Yinxiao Li School: Tsinghua High School Location: P. R. China,Beijing Academic Advisor: Jianjun Zhou Page - 163 N02 Application of Map Projection Transformation in Measurement of a Global Map Abstract: Cartographical projection is mathematical cartography. Map projection is the mathematical model of geoid. Gauss-Kruger projection is unable to realize seamless splicing between adjoining sheet maps. While Mercator projection, especially web Mercator projection, is able to realize seamless splicing but has larger measurement error. How to combine with the advantage of the two projections, apply the method of map projection transformation and realize accurate measurement under the framework of a global map, is the purpose of this article. In order to demonstrate that the problem of measurement could be solved by map projection transformation, we studied the mathematical principle of Gauss - Kruger Projection and the Mercator Projection and designed the algorithm model based on characteristics of both projections. And established simulated data in ArcMap, calculated the error of the three indicators-the area, the length and the angle- under areas in different latitude(0°-4°、30°-34°、 60°-64°)and longitude (120°-126°)range which validated the algorithm model. The conclusion suggests that it is feasible that using web Mercator Projection is capable to achieve a global map expression. Meanwhile, calculations of area, distance and angle using map projection transformation principle are feasible as well in Gauss - Kruger Projection. This algorithm combines the advantage of the two different kinds of projection, is able to satisfy uses' high demand and covers the shortage of measurement function of online map services in China.
    [Show full text]
  • Design of a Multiscale Base Map for a Tiled Web Map
    DESIGN OF A MULTI- SCALE BASE MAP FOR A TILED WEB MAP SERVICE TARAS DUBRAVA September, 2017 SUPERVISORS: Drs. Knippers, Richard A., University of Twente, ITC Prof. Dr.-Ing. Burghardt, Dirk, TU Dresden DESIGN OF A MULTI- SCALE BASE MAP FOR A TILED WEB MAP SERVICE TARAS DUBRAVA Enschede, Netherlands, September, 2017 Thesis submitted to the Faculty of Geo-Information Science and Earth Observation of the University of Twente in partial fulfilment of the requirements for the degree of Master of Science in Geo-information Science and Earth Observation. Specialization: Cartography THESIS ASSESSMENT BOARD: Prof. Dr. Kraak, Menno-Jan, University of Twente, ITC Drs. Knippers, Richard A., University of Twente, ITC Prof. Dr.-Ing. Burghardt, Dirk, TU Dresden i Declaration of Originality I, Taras DUBRAVA, hereby declare that submitted thesis named “Design of a multi-scale base map for a tiled web map service” is a result of my original research. I also certify that I have used no other sources except the declared by citations and materials, including from the Internet, that have been clearly acknowledged as references. This M.Sc. thesis has not been previously published and was not presented to another assessment board. (Place, Date) (Signature) ii Acknowledgement It would not have been possible to write this master‘s thesis and accomplish my research work without the help of numerous people and institutions. Using this opportunity, I would like to express my gratitude to everyone who supported me throughout the master thesis completion. My colossal and immense thanks are firstly going to my thesis supervisor, Drs. Richard Knippers, for his guidance, patience, support, critics, feedback, and trust.
    [Show full text]
  • Web Mercator Projection and Raster Tile Maps
    Annual Conference – 2017 – Ottawa May 31- June 2, 2017 Web Mercator Projection & Raster Tile Maps Two cornerstones of Online Map Service Providers Emmanuel Stefanakis Dept. of Geodesy & Geomatics Engineering University of New Brunswick [email protected] Online Map Service Providers O Available for ~12 years O Well established (difficult to remember how life was without them) 2 Online Map Service Providers 3 Online Map Service Providers Challenges ? • Technological • Cartographical 4 Online Map Service Providers Framework Request (where/what/resolution) CLIENT SERVER HTTP Map Product Map Service End-users Map Repository (Data+Images) 5 Technological Challenges O High and steadily increasing demand O Voluminous data (vectors and images) O Bandwidth limitations O Concurrent access O Security issues O Data protection 6 Cartographical Challenges O Visualize the map on Web browser O flat/rectangular monitor O Multi-resolution representation O various zoom levels O Multi-theme mapping O various themes (layers) O Multi-language mapping O various languages 7 Online Map Service Providers Web Mercator Projection Raster Tile Maps 8 Map Product Flat Monitor Request (where/what/resolution) CLIENT SERVER HTTP Map Product Map Service Map Repository (Data+Images) 9 Map Projection O A function f ... φ Y λ (Χ,Υ) ƒ(φ, λ) X 10 Choose a Map Projection 11 Choose a Cylindrical O Best fit O Rectangular grid 12 Conical Projection ? 13 Conical Projection ? 14 Cylindrical Projection ? 15 Cylindrical Projection O Simulation of a cylindrical projection 16 Cylindrical
    [Show full text]
  • Map Projections, Tiles & Copyright
    Institute of Cartography and Geoinformation Map Projections, Tiles & Copyright Ionuț Iosifescu ETH CAS RIS | | Module From GIS Data to Interactive Web Maps Map Projections, Tiles & Copyrights 17/02/2016 1 Institute of Cartography and Geoinformation Goal § Prepare data as tiled maps (similar to Google Maps) for integration into a Web Map Framework Learn / review § …what a map projection is § …the concept of zoom level (vs. map scale) § …what map tiles are needed for § …what is CartoCSS and TileMill § …why should we be aware of copyright ETH CAS RIS | | Module From GIS Data to Interactive Web Maps Map Projections, Tiles & Copyrights 17/02/2016 2 Institute of Cartography and Geoinformation Map Projections § Reference: sphere / ellipsoid § Distortions; e.g. WGS84, ETRS89 § Mapping surface: cylinder, cone, plane 2003 (c) Voser § Distortions § Aspect: orientation of the surface to the globe: normal, transverse, oblique § Tangent or secant to the sphere / ellipsoid § Preservation of metric properties: § Conformal or orthomorphic: locally no angular distortion (e.g. Transverse Mercator) § Equivalent or authalic: locally equal-area properties § Partially equidistant § Others (compromise or error minimizing) ETH CAS RIS | | Module From GIS Data to Interactive Web Maps Map Projections, Tiles & Copyrights 17/02/2016 3 Institute of Cartography and Geoinformation Plate Carrée § Equirectangular projection § North-South distances neither stretched nor compressed § Neither equal area nor conformal § The standard parallel is the equator § De facto standard
    [Show full text]
  • Implications of Web Mercator and Its Use in Online Mapping
    ARTICLES Implications of Web Mercator and Its Use in Online Mapping Sarah E. Battersby Department of Geography / University of South Carolina / Columbia / SC / USA Michael P. Finn Center of Excellence for Geospatial Information Science / United States Geological Survey (USGS) / Denver / CO / USA E. Lynn Usery Center of Excellence for Geospatial Information Science / United States Geological Survey (USGS) / Rolla / MO / USA Kristina H. Yamamoto National Geospatial Technical Operations Center / United States Geological Survey USGS / Denver / CO / USA ABSTRACT Online interactive maps have become a popular means of communicating with spatial data. In most online mapping systems, Web Mercator has become the dominant projection. While the Mercator projection has a long history of discus- sion about its inappropriateness for general-purpose mapping, particularly at the global scale, and seems to have been virtually phased out for general-purpose global-scale print maps, it has seen a resurgence in popularity in Web Mercator form. This article theorizes on how Web Mercator came to be widely used for online maps and what this might mean in terms of data display, technical aspects of map generation and distribution, design, and cognition of spatial patterns. The authors emphasize details of where the projection excels and where it does not, as well as some of its advantages and disadvantages for cartographic communication, and conclude with some research directions that may help to develop better solutions to the problem of projections for general-purpose, multi-scale Web mapping. Keywords: online mapping, Web Mercator, map projections, GIScience, cartography RE´SUME´ Les cartes interactives en ligne sont devenues un moyen populaire de communiquer au moyen de donne´es spatiales.
    [Show full text]
  • DGIWG 124 Defence Profile of OGC's Web Map Tile Service
    DGIWG 124 Defence Profile of OGC’s Web Map Tile Service 1.0 Document type: Standard Document subtype: Implementation Profile Profile of: The Open Geospatial Consortium’s Web Map Tile Service (WMTS) Implementation Standard, v.1.0.0 (OGC 07-057r7) Document date: 17 October 2017 Edition: 1.0.0 Responsible Party: Defence Geospatial Information Working Group (DGIWG) Audience: This document is approved for public release and is available on the DGIWG website, http://www.dgiwg.org/dgiwg/. Abstract: This document is a profile of OGC 07-057r7, v.1.0.0, dated 2010-04-06. It defines specific Defence requirements, recommendations and guidelines for implementations of a Web Map Tile Service. Copyright: (C) Copyright DGIWG, some rights reserved - (CC) (By:) Attribution You are free: - to copy, distribute, display, and perform/execute the work - to make derivative works - to make commercial use of the work Under the following conditions: - (By:) Attribution. You must give the original author (DGIWG) credit. - For any reuse or distribution, you must make clear to others the license terms of this work. Any of these conditions can be waived if you get permission from the copyright holder DGIWG. Your fair use and other rights are in no way affected by the above. This is a human-readable summary of the Legal Code (the full license is available from Creative Commons <http://creativecommons.org/licenses/by/2.0/ >). STD-DP-18-001 17 October 2017 Table of Contents EXECUTIVE SUMMARY ....................................................................................................
    [Show full text]
  • Some Principles of Web Mercator Maps and Their Computation
    © Bundesamt für Kartographie und Geodäsie 2020, Datenquellen Some Principles of Web Mercator Maps and their Computation Thomas F. Sturm March 5, 2020 DOI: 10.18726/2020_3 urn:nbn:de:bvb:706-6400 Thomas F. Sturm Some Principles of Web Mercator Maps and their Computation University of the Bundeswehr Munich March 5, 2020 Corrected March 31, 2020 DOI: http://doi.org/10.18726/2020_3 URN: urn:nbn:de:bvb:706-6400 Except where otherwise noted, this work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0). https://creativecommons.org/licenses/by/4.0/ Prof. Dr. Dr. Thomas F. Sturm Professur für Mathematik, insbesondere Technomathematik Institut für Mathematik und Informatik Fakultät für Betriebswirtschaft Universität der Bundeswehr München Werner-Heisenberg-Weg 39 D-85577 Neubiberg, Germany https://www.unibw.de/bw/professuren/thomas-sturm [email protected] Some Principles of Web Mercator Maps and their Computation Some Principles of Web Mercator Maps and their Computation Thomas F. Sturm March 5, 2020 Abstract The Web Mercator projection is used widely for online interactive maps. Despite discussions of the appropriateness of a simplified spherical approach or fundamen- tal reservations against the Mercator projection in general, its broad availability for everyone gives it a great significance. For example, OpenStreetMap provides free ge- ographical data which is typically accessed by means of map tile servers which rely on the Web Mercator projection. In this paper, starting with the mathematical deriva- tion of spherical Mercator projections, the error introduced by identifying ellipsoidal and spherical coordinates is analyzed, the map tile disassembling is described in full detail and map applications are given.
    [Show full text]
  • Web-Based Information System for Modeling and Analysis of Parameters of Geomagnetic Field
    Available online at www.sciencedirect.com ScienceDirect Procedia Computer Science 59 ( 2015 ) 73 – 82 Web-Based Information System for Modeling and Analysis of Parameters of Geomagnetic Field Andrei V. Vorobeva*, Gulnara R. Shakirovaa aUfa State Aviation Technical University, Ufa, 450000, Russia Abstract Today the specialists in many scientific and applied spheres (such as biology, medicine, geophysics, geology, technics, sociology, psychology and many others) consider parameters of geomagnetic field and its variations as one of the key factors, which can influence on systems and objects of various origins. The estimation of the influence requires an effective approach to analyze the principles of distribution of geomagnetic field parameters on the Earth’s surface, its subsoil and in circumterrestrial space. The approach causes a complicated problem to be solved, which is concerned with modeling and visualization of geomagnetic field and its variations parameters. The most effective and obvious solution to this problem is supposed to be an information system, because of the data-centric character of the problem itself. In spite of wide variety of approaches for mathematical modeling and graphical visualization of various data a problem of modeling, automated analyzing and 2D/3D- visualization of geomagnetic field and its variations is still not solved. In this paper the authors suggest the solution, which is based on modern geoinformation and web technologies and provides the mechanisms to calculate, analyze and visualize parameters of geomagnetic field and its variation. ©© 20152015 The The Authors. Authors. Published Published by Elsevierby Elsevier B.V. B.V.This is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of organizing).
    [Show full text]
  • Tmap: Thematic Maps in R
    JSS Journal of Statistical Software April 2018, Volume 84, Issue 6. doi: 10.18637/jss.v084.i06 tmap: Thematic Maps in R Martijn Tennekes Statistics Netherlands Abstract Thematic maps show spatial distributions. The theme refers to the phenomena that is shown, which is often demographical, social, cultural, or economic. The best known thematic map type is the choropleth, in which regions are colored according to the dis- tribution of a data variable. The R package tmap offers a coherent plotting system for thematic maps that is based on the layered grammar of graphics. Thematic maps are cre- ated by stacking layers, where per layer, data can be mapped to one or more aesthetics. It is also possible to generate small multiples. Thematic maps can be further embellished by configuring the map layout and by adding map attributes, such as a scale bar and a compass. Besides plotting thematic maps on the graphics device, they can also be made interactive as an HTML widget. In addition, the R package tmaptools contains several convenient functions for reading and processing spatial data. Keywords: thematic maps, spatial data, R. 1. Introduction Visualization is important in statistics and data science. Without looking at the data, it is difficult to understand the underlying phenomena, to unveil anomalies, and, moreover, to extract valuable knowledge (Tufte 1983). Software tools to visually explore, analyze, and present data are therefore greatly needed. The R environment (R Core Team 2017) and its extension packages contain many possibilities to craft elegant and clarifying graphics, most notably package ggplot2 (Wickham 2009). Although it is possible to achieve great looking geospatial visualizations in R, the required programming is often complicated and the available functions are often limited in terms of features and flexibility.
    [Show full text]
  • Geodesy, Map Projections and Coordinate Systems GIS in Water Resources, Fall 2015
    Geodesy, Map Projections and Coordinate Systems GIS in Water Resources, Fall 2015 Besides this synopsis, please read the overview of Georeferencing and coordinate systems in the ArcGIS Resource Center: and the section in the ArcGIS Help on Map Projections: http://resources.arcgis.com/en/help/main/10.2/#/What_are_map_projections/003r00000001000000/ For additional information on this subject, see National Research Council (2010). Geodesy is “the branch of the earth sciences that deals with the measurement and representation of the earth, including its gravitational field” (definition from Wikipedia). Geodetic or geographic locations on the earth are defined by latitude (φ), longitude (λ) and elevation (z), where the horizontal coordinates (φ, λ) are measured using angular units, and the vertical coordinate (z) is measured using distance units. A global positioning system (GPS) uses distance measurements from a collection of satellites to determine geodetic location. Distance is measured by taking the time difference between the time a signal is emitted from the satellite and the time it reaches the receiver and multiplying by the speed of light. A combination of signals from four satellites is sufficient to determine a point on the earth’s surface uniquely. The Continuously Operating Reference System (CORS) is a set of fixed GPS receivers whose position is known so accurately that it can be used to track the movement of tectonic plates, which is about 2-3 cm/year on the North American plate on which most of the continental United States rests, and a significantly large velocity on the Pacific plate on coastal California is located. This leads to adjustments in the location of survey benchmarks to reflect their position at a particular point in time.
    [Show full text]