A coordinate system is a reference system used to represent the locations of project data within a common coordinate framework. Coordinate systems are geographic (latitude-longitude), geocentric (X, Y, Z), or projected (X, Y). A coordinate system can optionally include a vertical datum that defines the origin for height values. Each coordinate system is defined by a Well-Known Text (WKT) definition string, a simple structured, text-based format for spatial reference system information that is easy to store and share between systems (See http://portal.opengeospatial.org/files/?artifact_id=999 and https://en.wikipedia.org/wiki/Well-known_text_representation_of_coordinate_reference_systems).
When layers are added to a TerraBuilder, TerraExplorer, or PhotoMesh project, they are reprojected to the project's coordinate system. If a layer does not include coordinate system information or the application is unable to read this information, you can indicate the coordinate system of this source, as provided by the data supplier, in the Coordinate System dialog box. The application then converts the layer data to the project’s coordinate system. Although the source file retains its original coordinate system, it is placed on the terrain according to the reprojection parameters.
If your project layers use coordinate systems with different vertical datums, vertical datum grid shift files in GTX format are used to shift and transform between these datums, by offsetting the vertical input coordinates by a specific amount. Sometimes the Well-Known Text (WKT) of one of the coordinate systems in your project references a particular GTX file that was not bundled with your installation, or the reference itself is missing from the WKT. In this case, you can manually add the missing GTX information. More about: How to add missing GTX information >
The Coordinate System dialog box is a high-level dialog box that allows you to select, view, and edit a coordinate system. You can also use this dialog box to define new coordinate systems that are not already defined. More about: Using the coordinate system dialog box >