Dear all,
Thanks again for feedbacks !
The decoding method is quite dense, because we had to take into account the fact that sometimes there are mistakes in reports.
For example, when no visibility known, there should be //// , no wind should be //////KT , no wind direction should be ////15KT, but sometimes they omit completely the block, or mix them up.
Some pressures are in inches (ETAR Ramstein air base, for example).
Some visibilities are in SM (US weather), other are in meters. Sometimes even kilometers ! (have seen "70KM" in austria).
Some winds are in KT, some other in MPS (Sofia, for example).
Temperatures were also a deep problem. because sometimes missing, sometimes not at the right position...
Sometimes clouds are BKN050, but sometimes they are BKN050TCU or BKN050CB or BKN050/// !
Automatic METARs have also some "special features". :-)
etc.
Some deeper mistakes sometimes : I've seen RA (rain) given before wind !
And even once, the 2000 meters visibility had been written with the last character : letter O instead of number 0 ! (two - zero - zero - O letter)
Which makes no difference for your eyes, but was not decoded properly by the computer.
So we had to take into account, not only the blocks in order, but also to analyze each block.
So first we split the message : all until weather, and decode that first part.
Includes RVR decoding if needed, which is a long sequence to interpret correctly because there are quite a lot of possible suffixes (until now, max 2 different RVR are decoded per airfield, but soon I'll modify that and there will be no limit thanks to a loop... I've seen one single metar with 5 different RVR once !).
Then look for CAVOK.
Then extract special blocks (pressure, temp, NOSIG...) and analyze.
Then a weather analysis thanks to a weather codes database (Rain, Sand, Ice crystals, Fog...).
Then a progressive loop to analyze layers and find ceiling, except if CAVOK, SKC, CLR, NCD.
Then add suffixes (some BECMG and special features not usual in METARS)
So we haded some scripts to make it able to also interpret codes which are usually not allowed by the strict METAR rules, but that are used by some meteorologists.
Each time we find a bug (99% due to an errorwhen the METAR was edited, not respecting the legal form) we modify the code to make it able to handle such errors and give a correct interpretation, that's why the code becomes more and more dense as time goes by
, and interpretations are more and more reliable (those few errors usaually make the script to considere weather stronger than it is actually).
But we still provide the original METAR, because there is no machine nor computer able to handle all possible human errors :-)
And we also have to pay attention to the fact that the code mustn't become too heavy, otherwise the page loading will be excessively long (especially for the whole European chart, there are nearly 500 airfields depicted).
Thanks BackPacker to have reported the error with the missing wind, you are completely right that is the reason for the wrong decoding of vis. I'll check that next week end to improve the code !
Alexandra
ORBIFLY IFR SCHOOL
PS : For Ukraine : next time we improve the chart I'll remember to extend it more east ! Right now there are only 2 fields available on the map : LRTR Timisoara and LRSM Satu Mare, with winds in meters per second :-)
I assume you would have liked Kiev, Minsk, Sebastopol and Chisinau ?