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## Topographical Basepoint of Hungary

Hidden : 02/24/2010
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### Geocache Description:

Geodesy also called geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three-dimensional time-varying space. Geodesists also study geodynamical phenomena such as crustal motion, tides, and polar motion. For this they design global and national control networks, using space and terrestrial techniques while relying on datums and coordinate systems.

In geodesy, point or terrain heights are "above sea level", an irregular, physically defined surface. Therefore a height should ideally not be referred to as a coordinate. It is more like a physical quantity, and though it can be tempting to treat height as the vertical coordinate z, in addition to the horizontal coordinates x and y, and though this actually is a good approximation of physical reality in small areas, it quickly becomes invalid for regional considerations.

Heights come in the following variants:

1. Orthometric heights - The orthometric height is the distance H along a line of force from a given point P at the physical surface of an object to the geoid.
2. Normal heights - Normal heights are heights above sea level, one of several types of height which are all computed slightly differently.
3. Geopotential heights - is a vertical coordinate referenced to Earth's mean sea level - an adjustment to geometric height (elevation above mean sea level) using the variation of gravity with latitude and elevation.

Each has its advantages and disadvantages. Both orthometric and normal heights are heights in metres above sea level, whereas geopotential numbers are measures of potential energy (unit: m2s-2) and not metric. Orthometric and normal heights differ in the precise way in which mean sea level is conceptually continued under the continental masses. The reference surface for orthometric heights is the geoid, an equipotential surface approximating mean sea level.

 The term above mean sea level (AMSL) refers to the elevation (on the ground) or altitude (in the air) of any object, relative to the average sea level datum. AMSL is used extensively in radio (both in broadcasting and other telecommunications uses) by engineers to determine the coverage area a station will be able to reach. It is also used in aviation, where all heights are recorded and reported with respect to AMSL (though also see flight level), and in the atmospheric sciences. The concept of a "mean sea level" is in itself rather artificial, because it is not possible to determine a figure for mean sea level for the entire planet, and it varies quite a lot even on a much smaller scale. This is because the sea is in constant motion, affected by the high and low pressure zones above it, the tides, local gravitational differences, and so forth. The best one can do is to pick a spot and calculate the mean sea level at that point and use it as a datum. For example, the Ordnance Survey uses a height datum based on the measurements of mean sea level at a particular gauge at Newlyn, Cornwall from 1915 to 1921 for their maps of Great Britain, and this datum is actually some 80 cm different from the mean sea level reading obtained on the other side of the country. An alternative is to base height measurements on an ellipsoid of the entire earth, which is what systems such as GPS do. In aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define mean sea level. Another alternative is to use a geoid based datum such as NAVD88.

The first levelling in Hungary has been carried out by the Military Geography Institute of Vienna between 1873-1913. The average level of the Adriatic Sea has been chosen for the base level and has been measured on Molo Sartorio’s scale in Trieste, 1875. Years later the level has been measured again with the result of an alteration of 9 cms hence the Base Level of Nadap has been initiated. That means the height level is based not on the sea level but on a virtual level which is 173,8385 metres below the Nadap Basepoint.
Later on, seved additional main basepoints hae been initiated to help further levelling. Only the Nanap one can be found within the current borders of Hungary which is the reason for the re-usage of the Base Level of Nadap in the levelling process of 1921 and 1949. The Nadap Basepoint’s height above sea level has been determined as 173,8385 metres in 1888. The Nadap one is the most stable point of Hungary in terms of geology.
It’s been ordained in the Eastern Bloc in 1960 to change from the Adriatic base level to the Baltic one. That resulted the shift to the Baltic (Kronstadter) base level which is 67,47 cms higher than the Level of Nadap. The height of Nadap Basepoint is 173,1638 metres according to the Baltic base level.

To log your visit at this earthcache,

1. How much is the difference between the average level of the Baltic Sea and Adriatic Sea?
2. What was the reason for choosing this site for the fundamental bench mark?
3. Measure the height of the basepoint - (magasságszelvény)

• Take a photo of yourself at the site, similar to the one provided within the listing.

Happy caching!

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A geodézia vagy földméréstan, a Föld alakjának és méreteinek meghatározásával, valamint a Föld felszínén levo természetes alakzatok és mesterséges objektumok alakjelzo pontjainak meghatározásával foglalkozó tudomány.
A geodézia az élet sok területén nélkülözhetetlen; a földbirtok- és országhatárok, valamint az épületek alapjainak kituzése, a térképek készítéséhez szükséges terepfelmérések elvégzése, de a földrajzi helymeghatározás és a navigáció is a földméréstan feladata. A geodézia és a térképészet rendkívül szorosan kapcsolódik egymáshoz, mivel a térkép nem más, mint a földmérok által meghatározott pontok helyzetének grafikus ábrázolása, esetenként kiegészítve a rendeltetésének megfelelo tematikus információkkal (turista-, autós-, topográfiai- stb. térképek).
Fontos és gyakori geodéziai munka a szintezés; ennek során a pontok egymás közti magasságkülönbségét és/vagy a pontok alapfelület (tengerszint) feletti magasságát mérik. Ezeket a munkákat az Országos Szintezési Hálózat alappontjaira támaszkodva hajtják végre. Építkezéseket minden alkalommal szintezés elozi meg, hogy biztosítsák: vízszintes, sima felületre épül az építmény.
Földmérési munkák végzése során a felmérendo pontokat szükséges megjelölni valamilyen módon, ez történhet ideiglenes módon, amikor csak a munkálatok idejére jelöljük meg a pontokat, a fontosabb pontjeleket azonban állandósítani kell.
A tengerszint feletti magasság vagy abszolút magasság a földrajzi pontok magasságának méréséhez meghatározott mérték. Alapja általában a legközelebbi tenger középvízszintje.

A megtaláláshoz kérlek
• válaszolj e-mailben a következo kérdésekre:

1. Mekkora a különbség az Adriai és a Balti tengerszint között?
2. Miért választották pont ezt a helyszínt az osjegy elhelyezésére?
3. Mérd meg a magasságszelvény földtol mért magasságát

• Tölts fel magadról egy GPS-sel egy képet a logod mellé, melyet a helyszínen készítettél – lásd példafotó

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1.0.1 listing, is optimised for 16:9, wildscreen monitors.