Euref coordinates: UTM or NTM?
Introduction
To be able to specify the location of a point in an unambiguous way we use coordinates. These are generally cited in meters or degrees. For unique coordinates it is important to specify which coordinate system we are using. The coordinate system is a reference system that defines a zero point in which coordinates are based. There are separate heights reference system, but we will not focus on it. The coordinate systems we will talk about refers to location in the horizontal plane (two-dimensional).
We need to reproduce the Earth's shape as a mathematical figure, an ellipsoid, scaling it down to a handy size and "peel" it so that we get a flat map. It is the map projection that depicts or "peels" ellipsoid.
Earth is round, while the map is flat. The way we depict the round earth on a flat map called Map Projection. Very simply explained, one can see on a map projection that way one peels off the earth's surface and scattered pieces into a coherent flat map.
Norway has two official coordinate system: EUREF89 UTM and EUREF89 NTM. Figure 1 shows what coordinate system is built from. Since both coordinate systems use datum EUREF89 we only have one official datum in Norway, but two official map projections, UTM and NTM.
Both UTM (Universal Transversal Mercator) and NTM (Norsk Transversal Mercator) are, as the name indicates, types of horizontal cylinder projections. Both are divided into zones where zone width is defined in degrees from the center of the earth (north / south axis) and to the ground surface in east-west direction.
UTM stands for Universal Transversal Mercator and is a horizontal cylinder projection. The coordinates are referenced in the number of meters from the equator (north coordinate) and the number of meters from central meridian (east coordinate).
NTM represents Norwegian Transversal Mercator and a horizontal cylindrical projection such as UTM. The difference is that NTM is a tangent map projection while UTM in practice is a glaring map projection. NTM has zone widths of 1 ° to prevent the large scale error introduced in UTM. That way, Norway is divided into a total of 25 zones for NTM, while only 3 zones will be UTM.
Transformation and conversion between coordinate
All map information is managed in EUREF89 UTM, and one has to make one transformation or conversion if you want to use the NTM projection, respectively or a local reference system.
In a transformation one must have several common known points in both coordinate systems and then make a calculation. This is done using software, but one will lose some of the accuracy of the original system. If one has a project in a local reference system and wants to transform this into UTM, it will lose some preciseness.
In a conversion, there is only a set mathematical calculation model needed to get one coordinate system over to another. With this method, therefore, the accuracy does not decrease, and one can use the same set of mathematical calculation model each time. If one has a project in the NTM projection and has to convert it to UTM, one makes the conversion and does not lose any accuracy from it original system. No matter if you make a transformation or conversion, you will not be able to transform or convert kloto times. This is because the file formats (SOSI) used today do not support it.
We don't convert UTM to NTM or vice versa, since this means responsibility to A-lab. If you need to change coordinates please send it to a survey professional.
NTM soner
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