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