Introduction

Many applications which use Cactus will want to make use of coordinate systems. The CoordBase thorn provides a method of registering coordinate systems and their properties. Thorns which implement coordinate systems will register the systems they provide with CoordBase. Since coordinate systems are composed of a collection of coordinates, the coordinates which comprise the systems are registered with CoordBase as well. The data describing coordinate systems are held on Cactus key-value tables. A schema for the format of these tables is provided in section A3.7. Developers are free to compose and use their own schema, but are encouraged to use the one detailed here, as this will be the standard for all of the core Cactus thorns.

CoordBase specifies an extensible set of coordinate properties. The use of key-value tables to hold these properties makes CoordBase flexible and configurable. The coordinate values themselves can be specified in a number of ways, depending on the nature of the coordinate system. This way symmetries of the coordinates on the computational grid can be exploited to minimize memory consumption. Via a function call, one can easily ascertain what coordinate system is associated with any given grid variable, which is convenient for e.g. I/O. A method of registering default coordinates for all grid variables of a certain dimension makes it simple to specify which coordinate systems should be associated with which grid variables.

The coordinate infrastructure provided by CoordBase will work seamlessly with AMR and multi-model codes.

Thorns which provide coordinates will inherit from CoordBase, and register both the coordinate systems they provide, and the default coordinate systems for the appropriate dimension of grid variables. In addition, one can associate a coordinate with any Cactus grid variable, within a thorn's interface.ccl. Coordinate systems specified in the interface.ccl override defaults for the dimension.

The coordinate functions in the Cactus flesh are deprecated with the introduction of this thorn. Please use the functions provided here in preference to those in the flesh.