Wind Arrow – Grib Reader. DISCLAIMER – PLEASE READ. This software is copyrighted software 2002 Jonathan Selby Xaxero Marine software and SkyEye systems Ltd. This program uses computer models of the world's weather download over the Internet. This data should be used with great caution and only used in conjunction with other methods of weather information. Use of this feature is strictly at the risk of the user. This program is a subset of the SkyEye Professional Satellite receiver that uses NOAA polar orbiting satellites to read and display real time weather photographs. For more information please visit www.xaxero.com Details This software reads in files available over the Internet to superimpose wind information over a SkyEye image or a CNAV vector plot. The information, when valid adds a huge amount to the satellite image allowing much easier interpretation of the overall data and normally giving you a very accurate picture of what is going on. The data required to supplement an image can be as small as 3 k compressed and is simple to download via a wireless link. These files are commonly referred to as GRIB files. They are primarily used to disseminate output data from very complex computer models of the world's weather. The GRIB file is an extremely flexible and all encompassing format that is beyond the scope of this document. Suffice to say that the software reads in a very small subset of that data that pertains to surface wind velocity and direction. If it is fed a GRIB file that does not have this data it will simply ignore the file. Publicly available data is put out primarily by the USA NOAA service. NOAA has several computer models that it uses for forecasting but only two of these models are relevant to SkyEye. The two models are "Global Forecasting System GFS" and "MMAB Operational Wave Model (wwave3)". GFS is extremely complex. The program models virtually every aspect of global meteorology. The wind data output from this model has quite often been suspect. More preferable is the (MMAB or wwave3). This a computer model designed to predict wave height, direction, and time period. In order to compute this data, it forecasts the surface wind speed and direction. Practical experience with this data set has shown it is extremely accurate in most cases. Internet download sites where relevant GRIB files can be downloaded from are: Global Marine Networks (GMN): www.globalmarinenet.net MaxSea www.navcenter.com RayMarine www.raymarine.com Global Marine Networks and Navcenter.com use the more reliable Wave model. Global Marine Networks have an Email robot that slices the grib files into manageable portions. This data is provided as a public service. gmngrib@globalmarinenet.net is a straight forward robot that takes requests for data in the Subject line and returns the requested grib information as an attachment. The data can be viewed with WindPlot and SkyEye Professional 6.31 To request information on it's use simply send e-mail to gmngrib@globalmarinenet.net and put the word "info" or "help" in the Subject line. To receive a 3-5K 24 hour forecast of the Atlantic region, for example, you would enter "Atlantic 24" in the subject line. And to receive a 10K 1 day forecast ( 4 forecasts in 6 hour intervals ) that can be animated for the same region enter "Atlantic 1day" on the subject line. The info file that is returned to you has detailed information on the command structure and use of the robot. Once you have downloaded the relevant files and saved them in a folder, SkyEye can read them. From the Chanel menu select Grib overlay. The wind arrow tool bar button can also be used. You are presented with a file open dialog. Navigate to the folder you want and select the grib file. The file will be opened and displayed on the satellite photo. Winds under 20 knots are displayed in blue. 20- 30 knots Magenta and over 30 knots are red. Each wind arrow has a yellow dot on the head indicating the direction the wind is traveling. A northerly wind will have the dot on the South end of the arrow. The length of the arrow is proportional to the wind speed and has a set of barbs on the end where the wind is blowing from to indicate speed. Each full barb is 10 knots and each half barb is 5 knots. Most grib files come as sets of data, with data enumerated every 3 hours or so. The current time of the data set being displayed is shown at the top of the window. You can use this box to select other time slices. You can also animate the wind arrows forward or backward in time via the + and – tool bar buttons. Although every attempt is made to test the software and ensure smooth operation over a wide range of data, there is always the possibility of a program fault. Please report any errors to xax@xaxero.com Jonathan Selby Xaxero Marine Software Engineering Ltd.