OpenPlotter – GRIB Files – Telecommunications, Navigation & Electronics

Introduction

OpenPlotter has many excellent features that we explored in previous posts (Ref.3-Ref.9). Weather information is critical for sailors and OpenPlotter features a GRIB file viewer as well as the ability to overlay this information on OpenCPN. The weather information is contained in GRIB files that can be downloaded over an internet connection either from cable/wifi/ssb/satellite etc.

GRIB Format

GRIB or Gridded Binary is a data format defined by the World Meteorological Organization to hold weather information (Ref.1/Ref.2). It is similar in concept to a .dem file used by Splat! to hold elevation information vs. Lat/Long. Typical relevant weather information would be:
*Surface wind speed and direction
*Surface atmospheric pressure, temperature, precipitation
*Visibility, cloud cover
*Wave height & direction
*Changes over several day period

XyGrib Grib File Viewer

Figure 1 shows the OpenPlotter menu selection for XyGrib Viewer. When you open the viewer, first use your mouse to highlight your geographic area of interest. Then select the download menu item and the download menu opens as shown in Figure 2. You have a choice of various Atmospheric & Wave models as shown in Figure 3. File sizes depend on the size of the coverage area, grid density, number of items to be monitored and number of days/time interval.
For a download of 1deg_Lat x 1deg_Long, grid=0.25deg, 7day/3hrs, file size = 132Kbyte . Download time depends on the available bandwidth of the SSB/Satellite connection, so adjust the parameters accordingly:
Modem @ 1.2Kbps = 14.7min, @ 2.4Kbps = 7.3min, @ 4.8Kbps = 3.7min, @ 9.6Kbps = 1.8min

Fig.1 OpenPlotter Menu Selection XyGrib file viewer

Fig.2 XyGrib Interface for GRIB Download

OpenCPN View

Once you have downloaded the Grib file, you can also view it in OpenCPN. On the left hand side menu, select “Grib” and then select the previously saved file. Mouse over a location to display wind speed for example as shown.