Geodesists study geodynamical phenomena such as crustal motion and polar motion. For this they design global and national networks, using space and terrestrial techniques while relying on datums. Geodesy — from the Ancient Greek word γεωδαισία geodaisia — is primarily concerned with positioning within the temporally varying gravity field, such geodetic operations are applied to other astronomical bodies in the solar system. It is the science of measuring and understanding the earths geometric shape, orientation in space and this applies to the solid surface, the liquid surface and the Earths atmosphere. For this reason, the study of the Earths gravity field is called physical geodesy by some, the geoid is essentially the figure of the Earth abstracted from its topographical features. It is an idealized surface of sea water, the mean sea level surface in the absence of currents, air pressure variations etc. The geoid, unlike the ellipsoid, is irregular and too complicated to serve as the computational surface on which to solve geometrical problems like point positioning.
The geometrical separation between the geoid and the ellipsoid is called the geoidal undulation. It varies globally between ±110 m, when referred to the GRS80 ellipsoid, a reference ellipsoid, customarily chosen to be the same size as the geoid, is described by its semi-major axis a and flattening f. The quantity f = a − b/a, where b is the axis, is a purely geometrical one. The mechanical ellipticity of the Earth can be determined to high precision by observation of satellite orbit perturbations and its relationship with the geometrical flattening is indirect. The relationship depends on the density distribution, or, in simplest terms. The 1980 Geodetic Reference System posited a 6,378,137 m semi-major axis and this system was adopted at the XVII General Assembly of the International Union of Geodesy and Geophysics. It is essentially the basis for geodetic positioning by the Global Positioning System and is in widespread use outside the geodetic community. The locations of points in space are most conveniently described by three cartesian or rectangular coordinates, X, Y and Z.
Since the advent of satellite positioning, such systems are typically geocentric. The X-axis lies within the Greenwich observatorys meridian plane, the coordinate transformation between these two systems is described to good approximation by sidereal time, which takes into account variations in the Earths axial rotation. A more accurate description takes polar motion into account, a closely monitored by geodesists
Carlos Viegas Gago Coutinho
On the journey down the Brazilian coast a heavy rain storm caused the aircraft’s engine to fail and the aviators were forced to ditch in the ocean. Realizing that something was wrong, the República sent out a distress signal asking other ships in the area to look out for the seaplane, after some time in the water, the aviators were found by a British freighter. The Paris City of the Reardon Smith Line, under Captain A. E. Tamlyn, en route from Cardiff to Rio, rescued Coutinho and Cabral, a commemorative painting of the rescue was produced by the Portuguese comic artist, José Stuart Carvalhais. Gago Coutinho invented a type of sextant incorporating two spirit levels to provide an artificial horizon and this adaptation of the traditional marine sextant allowed navigation without visual reference to the real horizon. He invented an optical instrument, to be mounted on the planes cockpit floor
Johannes Vingboons was a Dutch cartographer and watercolourist. Vingboons came from an artistic family and his father David Vinckboons was a successful painter and, of his five brothers, Philip Vingboons and Justus Vingboons were active as architects. Johannes Vingboons remained unmarried and lived with a part of his family in an Amsterdam house and studio on Sint Antoniesbreestraat, on the corner of Salamandersteeg. He began to paint and draw in the making of maps, five of the six sons were for a short or long time active as mapmaker, working together on them. From about 1640 until his death Johannes was a mapmaker, by combining his traditional expertise as a cartographer with his artistic qualities as a watercolourist, he produced water colors of exotic lands based on scrupulous research. These he based on reports and sketches that masters and merchants on their travels under the orders of the VOC, for many of these areas, his are the earliest images. Vingboonss work was unique and a sought after item in its own time for rich private individuals.
The largest batch, a series of 130 watercolours bound in three atlases, was bought in 1654 by queen Christina of Sweden, after her death these atlases came into the possession of Pope Alexander VIII, and now rest in the library of the Vatican. The next largest collection, more than hundred works, is in the possession of the National Archives in the Hague, a small number of watercolours are in the Medici library in Florence. Four signed parchment world maps form part of the collection of the Nederlands Scheepvaartmuseum in Amsterdam, a large part of his work were on show from 27 January to 15 April 2007 at the exhibition Land in zicht. Vingboons tekent de wereld van de 17e eeuw in the Kunsthal in Rotterdam, the majority had never been exhibited before and never will be again, because of the images vulnerability and small size. The three bound atlases left the Vatican papal library for the first time for the exhibition, architecten en kaartmakers in de gouden eeuw, Maarssen,1989, ISBN 90-6179-073-5 Martine Gosselink, Paul Brood, Land in zicht.
De wereld volgens Vingboons, Zwolle,2007, ISBN 90-400-8292-8
An islet is a very small island. As suggested by its origin as islette, an Old French diminutive of isle, use of the term implies small size, but little attention is given to drawing an upper limit on its applicability. Cay or Key – an islet formed by the accumulation of sand deposits atop a reef Motu – A reef islet formed by broken coral and sand. River island – A small islet within the current of a river, rock – A rock, in the sense of a type of islet, is an uninhabited landform composed of rock, lying offshore, and having at most minimal vegetation. Sandbar – An exposed sandbar is another type of islet, Sea stack – A thin, vertical landform jutting out of a body of water. Skerry – A small rocky island, usually defined to be too small for habitation, subsidiary islets – A more technical application is to small land features, isolated by water, lying off the shore of a larger island. Likewise, any emergent land in an atoll is called an islet. Tidal island – Often small islands lie off the mainland of an area, being connected to it in low tide.
In the Caribbean and West Atlantic, islets are often called cays or keys, rum Cay in the Bahamas and the Florida Keys off Florida are examples of islets. In the Channel Islands, they are identified by the suffix -hou from the Norse -holm. In Scotland and Ireland, they are often called inches, from the Gaelic innis, which originally meant island, in Ireland they are often termed skerries. In and around Polynesia, islets are widely known by the term motu, in and around the River Thames in England, small islands are known as aits or eyots. One long-term dispute over the status of such an islet was that of Snake Island, there are thousands of islets on Earth, approximately 24,000 islands and islets in the Stockholm archipelago alone. The following is a list of example islets from around the world, Islands or Rocks, Is that the Real Question. The Treatment of Islands in the Delimitation of Maritime Boundaries, in Myron H. Nordquist, John Norton Moore, Alfred H. A. The Law of the Sea Convention, US Accession and Globalization