Date:       9/20/02 11:40 PM
To:         Bulletins
From:       Luis Soltero
Copy:       
Blind Copy: 
Subject:    Weather Part III - Grib files


Hello All,

In the last two bulletins we discussed receiving and viewing weather 
received via the nws weather robot ftpmail.

We now turn our attention to a receiving and viewing a totally
different kind of weather product called a "Grib".  

A "Grib" file is a graphical weather product extracted from the NWS data
bank in "vectorized" format that contains prediction information
for the desired area.   Grib is vectorized as opposed to rasterized
which is what wefaxes are.   By vectorizing the data grib files
can be made much smaller than regular wefaxes.  They can
be displayed over charts and manipulated in much the same
way as vectorized electronic charts can be in say the Nobeltec
mapping program.

There are several advantages to grib files vs. regular wefaxes.
The main advantages are:
size, size, size, size, and size.  grib files are small.  They e-mail
very well.   They can also be tailored to include exactly the region
of interest.

There are some real disadvantages to grib files and they are
a) They are extracted directly from the output of computer generated
models with no human interpretation.  You need to know how
to interpret "raw" weather to use these.
b) they require special viewing software that will "draw" the vectorized
data over a chart so that you can interpret the scale.
c) The procedure required to request, get, and display the 
grib file is a bit more complex than with regular wefax data.

Typical grib files run between 5K to 20K.  They can be
much larger if you request a large area and more than
just pressure and wind direction and strength.   Most
of you will be downloading simple gribs and the size
will be small.

Requesting grib files...

Grib files are requested in much the same way that nws weather
is.  A request is made via e-mail to a mail robot which in turn
mails you a grib file as an attachment.  The easiest mail robot
to use that supports grib files is sponsored by our friends at
SailMail and is called saildocs.com.  Saildocs.com is run as
a public service for any one who needs its services.  There is
no charge and no registration required to use it.  Again the interesting
thing here is that most SailMail users can not use this service
to download grib files do to the time and size limitation constraints
placed on them by SailMail. Go figure....

Like the ftpmail robot, saildocs expects mail sent to it to contain
an empty subject line and a list of commands in the body of
the mesg.  The simplest mesg is the a query for help.

Sending a mail mesg to info@saildocs.com will result in
a 5K help file being e-mailed back to you.  The help file
describes in detail how to use saildocs. Note that the content
of the mesg sent to info@saildocs.com is totally ignored.  You
can send a "blank" mesg if you like.

To request a grib file you would send an e-mail to
query@saildocs.com
the subject is left blank and the body contains

send grib:10N,50N,10W,100W

where the format is grib:Lat1,Lat2,Lon1,Lon2 with
no spaces.  The saildoc help file describes variations
on this basic format. 

NOTE: Again, it's important to disable your signature
when interacting with the saildocs robot.

In the return mail you will find a grib file as an attachment.

Note that a calypso template can be created to automate
the download of grib files just like we did in the textual
weather example in the previous bulletin.

Viewing grib files...

As I mentioned above a special grib viewer program is required
to display the grib files. The good news is that there is one
available for free.  The bad news is that it's about 40Mbytes in
size.  If you have access to the Internet you can download a copy
from 

http://www.raymarine.com/raymarine/default.asp?site=1&section=3&page=145&Parent=0

Actually we have a link to this site in our weather links at www.marinenet.net
so no need to member the convoluted name.

For most of you out there downloading a 40 Mb file will be impossible.  The good news
is that many hams have a copy this already since they also download and display
grib files.  Some SailMail users may have it as well although as mentioned in
a previous bulletin wx via mail robot is not practical for them given the limitation
on their time and content size.  Anyway,  ask around.  Some one out there is bound
to have a copy.  I got my copy from Gene Ferris on Pangaea, Thanks Gene...

Install the and run the program.

The ray tech software is a full featured program that does a lot
more than just display grib files.  So, next we will do some 
configuration to simplify the display before we actually try
to do weather.  These changes that we are about to make
are a one time thing.  Follow the these instructions carefully.

On start up you should see lot's of buttons and a map of
Africa.  The first thing to do is get rid of all the stuff we don't
need.  Move your mouse to the top of the screen and in the
gray area to the right of the menu (make sure you are in the gray
area and that there are no menu items under your mouse) right
mouse click.  A menu should pop up.  Uncheck every thing in this
menu except "Standard toolbar" and "Weather toolbar".  Weather
tool bar is the last item on the menu.

On the left side of the display click on the "x" next to navigator======
to remove the navigator window.

Finally grab the
=
=
=
= 
bar to the left of the "weather toolbar" (it's the thing that says pressure,
wind, temperature, and currents) and move it up and right so that it
lands to the right of the standard tool bar and release it.

Now move the cursor to Brazil and click.  Then move the cursor to
the Caribbean and click again.  Or move to your geographical location
by using multiple mouse moves and clicks.  

We are almost done with the setup.  Now click on "Layers" on the
toolbar and double click weather.  Select "Scaled Arrows" under
Wind waves, wind, swell and wind waves,  and swell".  Select barbs
under ocean currents.

Now exit the program.

Back in calypso find the e-mail with the attached grib file and open
it.  Right mouse click on the attachment and select "Save As..."
now save the grib file in a location you wont forget.  The "desktop"
is a good place.  You are now done with calypso so exit the program.

Now we are going to display the grib file.

Run raychart.

Bang on Layers in toolbar and the double click on weather.  
now hit the browse button and find the grib file.  Look on
the desktop if that is where you located it.  Highlight the
file and click OK.  Hit OK again to exit the weather section
and the cancel to get back to the chart.  The grib data
should now be displayed overlaid on the chart.

If you are using my sample grib file above you should
see a weather chart for the entire N Atlantic.  Push the
"pressure" and "wind" buttons on the tool bar to make
the pressure lines and wind arrows display. Zoom in and 
out to view more/less detail.

And that's all folks....

--luis