Global Positioning System

The Global Positioning System NAVSTAR GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings block the weak GPS signals; the GPS does not require the user to transmit any data, it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS provides critical positioning capabilities to military and commercial users around the world; the United States government created the system, maintains it, makes it accessible to anyone with a GPS receiver. The GPS project was started by the U. S. Department of Defense in 1973, with the first prototype spacecraft launched in 1978 and the full constellation of 24 satellites operational in 1993.

Limited to use by the United States military, civilian use was allowed from the 1980s following an executive order from President Ronald Reagan. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes. In 2000, the U. S. Congress authorized the modernization effort, GPS III. During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability"; the GPS service is provided by the United States government, which can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War, or degrade the service at any time. As a result, several countries have developed or are in the process of setting up other global or regional satellite navigation systems; the Russian Global Navigation Satellite System was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s.

GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more and to within two meters. China's BeiDou Navigation Satellite System began global services in 2018, with full deployment scheduled for 2020. There are the European Union Galileo positioning system, India's NavIC. Japan's Quasi-Zenith Satellite System is a GNSS satellite-based augmentation system to enhance GNSS's accuracy in Asia-Oceania, with satellite navigation independent of GPS scheduled for 2023; when selective availability was lifted in 2000, GPS had about a five-meter accuracy. The latest stage of accuracy enhancement uses the L5 band and is now deployed. GPS receivers released in 2018 that use the L5 band can have much higher accuracy, pinpointing to within 30 centimeters or 11.8 inches. The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including classified engineering design studies from the 1960s.

The U. S. Department of Defense developed the system, which used 24 satellites, it was developed for use by the United States military and became operational in 1995. Civilian use was allowed from the 1980s. Roger L. Easton of the Naval Research Laboratory, Ivan A. Getting of The Aerospace Corporation, Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it; the work of Gladys West is credited as instrumental in the development of computational techniques for detecting satellite positions with the precision needed for GPS. The design of GPS is based on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator, developed in the early 1940s. In 1955, Friedwardt Winterberg proposed a test of general relativity – detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. Special and general relativity predict that the clocks on the GPS satellites would be seen by the Earth's observers to run 38 microseconds faster per day than the clocks on the Earth.

The GPS calculated positions would drift into error, accumulating to 10 kilometers per day. This was corrected for in the design of GPS; when the Soviet Union launched the first artificial satellite in 1957, two American physicists, William Guier and George Weiffenbach, at Johns Hopkins University's Applied Physics Laboratory decided to monitor its radio transmissions. Within hours they realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit; the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem—pinpointing the user's location, given the satellite's; this led them and APL to develop the TRANSIT system. In 1959, ARPA played a role in TRANSIT. TRANSIT was first tested in 1960, it used a constellation of five satellites and could provide a navigational fix once per hour. In 1967, the U.

S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology require

Architectural photographers

Early architectural photographers include Roger Fenton, Francis Frith, Samuel Bourne and Albert Levy. They paved the way for the modern speciality of architectural photography. Architectural photography had practitioners such as Ezra Stoller and Julius Shulman. Stoller worked on the east coast of America, having graduated with a degree in architecture in the 1930s. Shulman, based on the West Coast, became an architectural photographer after some images that he had taken of one of Richard Neutra's houses in California made their way onto the architect's desk. Architectural photography Perspective control lens Perspective control View camera International Association of Architectural Photographers-IAAP AIAP - The Association of Independent Architectural Photographers ASMP, Architectural Photographers Group ViewFinder - over 85,000 photographs from the archives of English Heritage

AfroBasket Women 2015

The 2015 FIBA Africa Championship for Women was the 22nd AfroBasket Women, played under the rules of FIBA, the world governing body for basketball, FIBA Africa. The tournament was hosted by Cameroon from 24 September to 3 October, with games played at the Yaoundé; the winners qualified for the 2016 Summer Olympics. Senegal won the title for the eleventh time by defeating hosts Cameroon 81–66; the draw was held on 9 May 2015. All times are local. 5th place bracket9th place bracket Most Valuable Player: Aya Traoré All-Star Team: PG – Deolinda Ngulela SG – Aya Traoré SF – Ramses Lonlack PF – Geraldine Robert C – Adaora Elonu Official website