Page History

This icon converts GRIB data into the format required by the VAPOR 3D visualisation system.

The macro language equivalent is vapor_prepare().

VAPOR input files

VAPOR input data is described by .vdf  (VAPOR Data Format) files. These are XML files containing the name and dimension of all the variables and the path of the actual data files storing the data values.  VAPOR stores its data values in .vdc (VAPOR Data Collection) files. These are NetCDF files containing wavelet compressed 3D data. There is a separate file for each variable and timestep organized into a folder hierarchy.

VAPOR grids

VAPOR input data must be defined on a 3D grid,  which has to be regular horizontally (on a map projection). The vertical grid structures supported by the Metview VAPOR interface are as follows: layered and regular.  

For layered grids VAPOR expects a parameter specifying the elevation of each 3D level in the input data. This is typically the case for  pressure or model level (η levels) data with height or geopotential available (or it can be computed).

For regular grids the 3D levels are supposed to be equidistant (in the user coordinate space). This type can be used when the data is available on equidistant hight levels.

The situation when pressure or model level data is present without height information is somewhat special. The grid in this case is not layered but can be regarded as regular in its own coordinate space (pressure or model levels) letting z axis simply represent pressure or model levels in the 3D scene rendered in VAPOR.

VAPOR uses a right-handed coordinate system which means that :

• the horizontal grid has to start at the SW corner
• the vertical coordinates have to increase along the z axis (upwards)

How does VAPOR Prepare work?

VAPOR Prepare reads GRIB data then generates the vdf and vdc files out of it. Internally it dumps GRIB data into a raw binary format then converts it into VAPOR format by using the raw2vdf VAPOR command line tool. VAPOR Prepare implicitly rearranges the grid to make it VAPOR compliant.