Definition

“A […] coordinate reference system (CRS) is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems. […] spatial reference systems can be referred to using a SRID integer, including EPSG codes …” (wikipedia.org, 2019).

The SRIDs and corresponding EPSG codes of all CRS can be found on spatialreference.org. The most common global CRS in latitude and longitude is WGS84 (used by the GPS satellite navigation system) with the following CRS string "+init=epsg:4326" as identifier.

Transform CRS in 3-D

The eRTG3D only supports calculations in Cartesian coordinate systems. In case of latitude / longitude data (e.g.: WGS84), these must be converted into a Cartesian coordinate system, as for example the Universal Transverse Mercator (UTM).

To carry out a CRS transformation, please use transformCRS.3d(), which is based on the st_transform() from the sf package. Therefore is supports CRS transformations in 3-D.

Note: spTransform() from the sp package only supports transformations in the 2-D plane, which will cause distortions in the third dimension.