5a5b67bab1
Yesterday night it occurred to me that the current handling of missing METAR strings isn't good enough: - in case of missing METAR strings, don't re-send the last successful string, but the last successful string sent to *this* client. (If one client is running in virtual December, it won't be happy about dropped in summer weather.) - fix a bug that allowed -vc notation (options -v and -c), but broke a lot of other notations (-b/var/tmp). Only -v can now be accumulated again, as in -vvvv.
281 lines
8.3 KiB
Text
281 lines
8.3 KiB
Text
FlightGear METAR proxy server
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=============================
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metarproxy is a caching proxy server for METAR data strings written in
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Perl. It can be used to:
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- provide METAR data for machines without internet connection
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- centralize METAR fetching: one machine in a network runs the proxy, all
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other connect to the proxy
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- deliver defined and reproducible weather for educational purposes
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- save weather situations for later use
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Quick instructions to try out:
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$ metarproxy --download 3h
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$ metarproxy --color &
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$ fgfs --proxy=localhost:5509 --time-offset=-2 --enable-real-weather-fetch
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To make use of the proxy, you have to:
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1. check if you want to use the default cache directory
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and other default settings, or change them accordingly
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2. make sure the cache is filled with METAR strings
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3. start the proxy server
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4. run fgfs with appropriate time and proxy settings
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1. Basic setup and preparing the cache
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======================================
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If you are happy with the defaults, you can well skip to the
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next section.
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1a. The cache directory
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-----------------------
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All metarproxy operation modes need access to a cache, either for
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storing or retrieving METAR strings. By default, the cache directory
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is $FG_HOME/metar, whereby $FG_HOME is either to be set as environment
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variable, or defaults to $HOME/.fgfs. $HOME, in turn, defaults to "."
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(the current working directory). In other words: if no provisions are
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made, you end up with /home/$USER/.fgfs/metar as your cache directory
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on Linux-like operating systems, and ./.fgfs/metar elsewhere.
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There are several ways to change the cache path:
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- change one of the environment variables, ideally $FG_HOME. This can
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be done in the system configuration in MS Windows, and in ~/.bashrc
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or ~/.profile etc. on Linux-like systems
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export FG_HOME=/var/tmp/metar
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- or on the command line when running metarproxy:
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$ FG_HOME=/var/tmp/metar metarproxy
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- you can also set the cache directory directly as a command line option
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--base or -b:
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$ metarproxy --base=/var/tmp/metar
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- this command line option can, together with any of the other metarproxy
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options, be stored again in an environment variable METARPROXY
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export METARPROXY="-c -vv -b/var/tmp/metar"
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1b. set metarproxy's proxy server
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---------------------------------
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metarproxy isn't only a proxy server itself, it can also use one to
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download METAR strings. By default it uses the one defined in the
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environment variable http_proxy (which is commonly used on Linux-like
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systems, and is, for instance, used by the lynx browser), or none if
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unset. To set a particular proxy server for HTTP download, use one of
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these methods:
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- set http_proxy globally: EXPORT http_proxy=http://localhost:3128/
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- or on the command line: $ http_proxy=http://localhost:3128/ metarproxy
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- unset http_proxy: $ http_proxy= metarproxy
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- use the command line option: $ metarproxy --proxy=http://localhost:3128/
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- set the option globally: EXPORT METARPROXY="-yhttp://localhost:3128"
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2. Fill the cache with METAR data
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=================================
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There are three operation modes to do that:
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2a. --download mode to download worldwide data sets
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2b. --install mode to install files from your system
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2c. --record mode to record a selection of stations over some period
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2a. --download mode
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-------------------
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You can download worldwide sets of METAR strings, each in a file of about
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1MB size from weather.noaa.gov[1]. This can be done with a separate ftp
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client or web browser, but it can also be done by metarproxy:
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$ metarproxy --download 3h ... download last three hours (~ 3MB)
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Note that the file for the *current* hour is only partly filled! You can
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use from 1h up to 24h. Alternatively, you can request particular hours:
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$ metarproxy --download 0 ... download first hour after midnight GMT
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Ranges are allowed, too:
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$ metarproxy --download 0-2 ... download first three hours after
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midnight GMT
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These three methods can be used in combination:
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$ metarproxy --download 6h 0-2 4
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Files downloaded this way aren't stored on your systems in the same form
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as they are offered under [1], but are already stored in the cache in a
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different way (see section 5). Redundant strings are not stored, so it's safe
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to --download the same hours more than once. This won't create duplicates.
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2b. --install mode
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------------------
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The --download mode needs a sufficiently cheap and fast internet
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connection. Sometimes it may be desirable to download the files directly
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from the links (see [1]) on one computer, to burn them on a CD and then
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to install them on the laptop. The downloaded files have names like
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00Z.TXT to 23Z.TXT, whereby the number stands for the hour when they
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were started. Only the last 24 hours are available for download.
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If GMT is 1800, then 18Z.TXT will be the currently written and most
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recent file. 19Z.TXT is already 23 hours old and will be overwritten
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in one hour. To install such files in the cache, do this:
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$ metarproxy --install 00Z.TXT 01Z.TXT
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or
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$ metarproxy --install ??Z.TXT
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etc.
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2c. --record mode
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-----------------
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To record a set of stations over a period, without the need to download
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several megabytes of data, you can use the record mode:
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$ metarproxy --record KSFO KOAK KNUQ KSJC KCCR
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The stations are then checked every 15 minutes and the METAR data
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stored in the cache. Additionally, you can specify one or more files
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with station IDs:
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$ metarproxy --record --file=$FG_HOME/station-list
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$ metarproxy --record EDDM --file=/tmp/Austria --file=/tmp/Hungary
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These files simply contain station IDs separated by spaces in one
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or more lines:
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$ cat /tmp/Austria
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LOWL LOWI LOWS LOWW LOWK LOWG
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LOXL LOXA LOXT
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Some of the IDs are logically assigned, so that you can create a list
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of, lets say, all Austrian METAR stations from FlightGear's METAR list:
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$ zgrep "^LO" $FG_ROOT/Airports/metar.dat.gz > /tmp/Austria
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$ zgrep "^ED" $FG_ROOT/Airports/metar.dat.gz > /tmp/Germany
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$ zgrep "^EG" $FG_ROOT/Airports/metar.dat.gz > /tmp/UK
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$ zgrep "^K" $FG_ROOT/Airports/metar.dat.gz > /tmp/USA
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Quit the --record mode by Ctrl-C or killing the program.
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3. run the metarproxy server
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============================
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assuming that the cache directory is already set, you just need to
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run the proxy:
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$ metarproxy&
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or with colored output and more log messages:
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$ metarproxy -c -vv
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The proxy listens to port 5509 by default, but you can easily let
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it use another port. As you can see, the proxy is quite liberal
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with respect to option syntax:
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$ metarproxy --port 1234
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$ metarproxy --port=1234
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$ metarproxy -p 1234
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$ metarproxy -p1234
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4. let fgfs use the metar proxy
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===============================
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All you need to do is point FlightGear to the metar proxy and let
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it run at a simulated time for which you actually have cached METAR
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data:
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$ fgfs --enable-real-weather-fetch --proxy=localhost:5509 \
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--start-date-lat=2005:01:12:12:00:00
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FlightGear will then fetch the metar data from the proxy as if it
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were weather.noaa.gov. If no appropriate data set is found at all,
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the proxy sends a default string. If data are found but older than
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250 minutes, then the last successful data are sent again.
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5. the cache organization
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=========================
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metarproxy puts all data for KSFO on 2005/1/19 into a directory
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2005-01-19/K/KS/KSFO. The date directory name is used to find all
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data for this day, but metarproxy will also look at the date in
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particular METAR strings. So, renaming the directory to 2005/1/20
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won't make the cached data available for the next day! You need
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to set fgfs' GMT date to 2005/1/19. Also, if the simulated GMT
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is midnight, then you will get midnight weather. You can't
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enjoy midnight weather at daylight. The cache always delivers
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the (past) real weather at simulated GMT.
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6. download addresses
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=====================
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Download addresses for the last 24 hours:
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http://weather.noaa.gov/pub/data/observations/metar/cycles/
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ftp://weather.noaa.gov/data/observations/metar/cycles/
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Addresses for the most recent METAR data strings of particular
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stations:
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http://weather.noaa.gov/pub/data/observations/metar/stations/
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ftp://weather.noaa.gov/data/observations/metar/stations/
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$Id$
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Melchior FRANZ <mfranz@aon.at>, 2005/1/24
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