<https://ru.coursera.org/lecture/aerial-photography-with-uav/types-of-coordinate-systems-and-vertical-datum-c1btB#lecture>
<http://schema.org/transcript>
"The ellipsoidal coordinates B and L are often converted to planar x and y coordinates in different cartographic projections. One of the types projections is a cylindrical projection, in which the surface of the ellipsoid is first projected onto the surface of the cylinder, and then the cylinder rotates to the plane. One of the commonly used projections is the transverse projection of the Mercator (Universal Transverse Mercator - UTM). In this projection, the ellipsoid is divided into 60 zones, each zone is 6 degrees in longitude. The scale on the initial meridian is 0.9996. Zones are counted from the initial meridian to 180 to the east. The Gauss-Kruger projection is widespread in Russia and the CIS countries. Its difference from the transverse projection of the Mercator is that the scale on the initial meridian is 1, and the zones are counted from the initial zero meridian to the east. On the plane of a projection, you can enter a system of plane rectangular coordinates. For example, in Russia a planar coordinate system is implemented on the plane of the Gauss-Krueger projection. The initial meridian is taken for the abscissa axis, and the equator line for the ordinate axis. Moreover, in order to avoid negative ordinates, the y value for the point on the initial meridian is set to 500 km. In front of each ordinate is assigned a zone number. Such a system of planar coordinates was implemented for the SK-42 reference system and adopted in the USSR as a state one and was used to create topographic maps. Also, the SK-63 planar coordinate system, which was obtained from SK42 by shifting and turning, was often used. It was established to avoid secrecy in large-scale cartographic works. In accordance with Order No. 271 of the Ministry of Economic Development dated June 6, 2017, the Gauss-Krueger projection and the corresponding plane coordinate system are still being used to create state topographic maps. Most often in topographic and geodetic practice, you have to work in local coordinate systems. The procedure for establishing local coordinate systems was approved by order of the Ministry of Economic Development No. 383 dated July 28, 2017. In accordance with this order. The local coordinate system is the CS established in relation to a local area not exceeding the territory of a subject of the Russian Federation. The beginning of the coordinate system, the coordinate axes of the local coordinate system must not coincide with the beginning of the coordinate system, the coordinate axes of the state coordinate system, used forof geodetic and cartographic works implementation. Local coordinate systems are established for geodetic and topographic work during engineering surveys, construction and operation of buildings and structures, land surveying, cadastre management and other special works. A mandatory requirement in establishing local coordinate systems is to enable the transition from a local coordinate system to a state coordinate system, which is carried out using transition parameters (keys). Each local coordinate system can be created from one or several three or six degree zones. The parameters of local coordinate systems and the keys to the transition to the state coordinate system are established by the Roseestr in agreement with the Ministry of Defense of the Russian Federation. When establishing a vertical datum, the decisive factor is the choice of the relativity surface and the starting point, whose height is assumed to be zero. Relativity surfaces are geoid and quasigeoid. Orthometric heights are counted from the surface of the geoid, and normal heights from the surface of the quasigeoid. In practice, geodetic heights which are counted from the surface of an ellipsoid (Earth or reference) are also used. A geoid is a figure of the Earth formed by a level (equipotential) surface of the gravity potential, which coincides with the surface of the World Ocean in a rest state and continues under the continents. An exact determination of the position of the geoid relative to the selected ellipsoid from ground-based measurements is impossible. Mathematically, a quasigeoid -- a surface close to a geoid -- can be determined strictly from ground-based gravity data. The mismatch between the geoid and the quasigeoid averages 2–5 cm in the lowlands and can reach 2 m in the highlands. The connection between geodetic and normal heights and between geodetic and orthometric heights is established by the relationships you can see on the slide. Normal heights are independent of the ellipsoid choice. The geodetic heights and the quasigeoid heights depend on the ellipsoid choice. Normal heights are displayed on topographic maps and are given in the coordinate directories of geodetic points. In accordance with Decree of the Government of the Russian Federation dated November 24, 2016 N 1240 “the 1977 Baltic Vertical datum is used as the state system of heights, the reference heights of which are taken from zero of the Kronstadt foot rod, which is a horizontal line on a copper plate, fortified in the mouth of the bridge over the bypass channel in the city of Kronstadt”"
<https://ru.coursera.org/lecture/aerial-photography-with-uav/types-of-coordinate-systems-and-vertical-datum-c1btB>