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User Manual / GRIB input to solver

The weather routing system has an easy to use system for selecting GRIB files to be used by the solver.

The process to have the solver use the file you want is normally composed of two steps:

  1. select the file you want.
  2. ensure the solvers starting point and time are both within the range of the file.

Understanding GRIB file selection.

There is a two step process used by the system to establish which GRIB file should be used the next time the solver is run:

  1. find a list of candidate files which meet the requirements for what is needed.
  2. choose the most recently selected file from the list of candidates.

The system uses this process to select the file to use for each of the categories: wind, wave height and current. The wave and current files are only chosen if the system settings have been enabled to allow those files.

For every file in the LuckGrib GRIB file librarian’s list of files, the system knows:

  1. the time span of the file.
  2. the region of the file.
  3. the parameters contained in the file.

The weather routing system knows the starting point and starting time for the route that will be calculated. To build the list of candidate files, the system looks for GRIB files which:

  1. contain the starting point.
  2. contain the starting time.
  3. contain the parameters needed for the type of file being assigned (wind, wave, current.)

Wind file: If the search is for a wind file, the search may be performed more than once if the vessel has been set to specify multiple wind files. If multiple wind files are being used, the candidate search and selection is done once for each search token and a list of wind files is returned.

Wave height file: If the search is for a wave height file, the file may contain more than one wave height parameter. If the file contains multiple height parameters, only one of them is used. In order, the preference is:

  1. HTSGW - significant height of combined wind waves and swell.
  2. WVHGT - significant height of wind waves.
  3. SWELL - significant height of swell waves. Primary swell before secondary.

Current file: If the search is for a current file, a file may be included in the candidate list if the start point is contained, or a target point has been provided and the file being examined contains the target point. This allows, for example, a high resolution current file to be used for a small region around the destination, while the starting point may not be covered.

There is additional information in the Getting Started / GRIB file selection section.

Wrong file?

If the file being selected by the system is not what you expect, try, in order:

  1. select the file you prefer. The most recently selected file is chosen from the candidate list.
  2. ensure the starting time and point are within the range of the file.

GRIB file buttons

Note that the file names shown in the configuration area are actually buttons. If you click on one of those buttons the system will switch to the indicated GRIB file. This allows you to quickly toggle between the wind file and current file, for example.

LuckGrib Weather Routing is currently only available on macOS. Support for iOS and iPadOS is under development.