Voir la source de Vgrid descriptors

This package contains a set of applications and a library of [[Fortran]] functions designed to assist with the manipulation and interpretation of the vertical coordinate (the '!!' record) in [[RPN STD file|RPN Standard Files (FST)]].   Descriptors and vertical coordinates can be created, queried and written using either the applications provided, or high- or low-level [[Fortran]] APIs.

== Background ==
A full set of 3D grid descriptors is needed to position a point in space.  These descriptors are <tt>>></tt>, <tt>^^</tt>, and <tt>!!</tt> for the x-dimension, y-dimension and z-dimension, respectively.  Each field in an FST file is linked to a set of horizontal grid descriptors using the convention:
 field:ig1 <-> horizontal_descriptor:ip1
 field:ig2 <-> horizontal_descriptor:ip2
Linking of the vertical grid descriptor follows a similar strategy The <tt>iv1</tt> and <tt>iv2</tt> values used for vertical coordinate linking are stored in a secondary record header.  This feature is currently unimplemented in RPN Standard files.:
 field:iv1 <-> vertical_descriptor:ip1
 field_iv2 <-> vertical_descriptor:ip2
The Vertical Grid Descriptor Module (see below) is a Fortran90 module that provides a simple interface for reading and interpreting vertical grid descriptors (<tt>!!</tt>).

=== Vertical Coordinate Descriptor ===
The vertical coordinate descriptor in [[GEM]] v4.0.0 and above is <tt>!!</tt> (toc-toc).  This record contains a table of information that is needed to establish the vertical coordinate.  This descriptor is backwards-compatible, in that it can be used to describe any coordinate that is currently in use at RPN/CMC.  For vertical coordinates that depend on a surface reference field, information about the reference name is contained in the descriptor record, and allows the user to reconstruct the position of each vertical level in the coordinates corresponding to the level type (i.e. pressure, height, etc).

== Vertical Grid Descriptor Module  ==

The vertical grid descriptor module is use-associated with
 use vGrid_Descriptors
and gives the user access to a both a [[Vgrid/highlevel|high-level interface]] and a [[Vgrid/lowlevel|lower-level interface]] for dealing with vertical grid descriptors in FST files. The [[Vgrid/highlevel|high-level interface]] is used to compute grid positions <tt>levels</tt> in the vertical in an easy one-step call. For example, computing the pressures at all levels of a set of hybrid coordinate levels produced by the GEM model is as simple as a single call to the <tt>levels</tt> method of the [[Vgrid/highlevel|high-level interface]]. The majority of users will probably be satisfied with the functionality of this level of interface.

:'''[[Vgrid/highlevel|Access High-Level Interface Documentation]]'''

The fundamental component of the [[Vgrid/lowlevel|lower-level interface]] to the module is the [[Vgrid/lowlevel#Vertical_Descriptor_Type|vgrid_descriptor derived type]], which contains all of the information necessary to read / write / manipulate the vertical descriptors of a file, along with providing some basic functionality such as computing vertical coordinate positions.

:'''[[Vgrid/lowlevel|Access Low-Level Interface Documentation]]'''

In addition to the interface documentation accessible above, a [[Vgrid/dev corner|Developer's Corner]] is provided to support further development of the ''Vertical Grid Descriptors'' module. This page contains information about the internal workings of the module that is of use to those actively developing the module, but that is not applicable to users.

== Compiling and Linking Against the Module  ==

The libraries for the ''Vertical Grid Descriptors'' package currently reside in an [[Ssm]] package, you may access it with:

{{Vgrid/setup}}

Using etagere (the build system supported at RPN/CMC), a program (called <tt>foo.ftn90</tt> in this example) that can makes use of the <tt>Vertical Grid Descriptors</tt> module through use-association can be compiled and linked against a specific version of the module (in this case 1.0.1) with the following command.

 # version 5
 r.compile -o foo -src foo.ftn90 -libappl descrip -librmn rmn_015
 # version 4
 r.compile -o foo -src foo.ftn90 -libappl descrip modelutils_base -librmn rmn_015

If an error message during compilation warns about an incompatible module version, check the [[Vgrid/release notes|release notes]] page for directions on which compiler version to acquire before compiling.

== Release Notes ==

== Vertical coordinates in fst files ==