---
title: "Processing METAR weather reports"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{pmetar}
  %\VignetteEncoding{UTF-8}
  %\VignetteEngine{knitr::rmarkdown}
editor_options: 
  markdown: 
    wrap: 72
---

```{r, label = "set options", include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  tidy = FALSE
)
```

# Package pmetar

Pmetar is an R package that allows to download and parse current or
historical METAR (Meteorological Terminal Aviation Routine Weather
Report) reports, mainly for airports.

**It has to be underlined that the package pmetar is not intended for
flight planning or navigation.**

## Downloading a current METAR weather report

For downloading a METAR report we need to know an airport four letters
ICAO code, International Civil Aviation Organization, or three letters
IATA code, International Air Transport Association.\
Let's download a current METAR weather report for Warsaw Okecie Airport.
Its ICAO, International Civil Aviation Organization, code is EPWA. A
report can be got from Aviation Weather Center
<https://aviationweather.gov/data/metar/>

```{r get a METAR report with ICAO code}
library(dplyr)
library(pmetar)
metar_get("EPWA")
```

Now let's take a look at Newark Liberty International Airport, EWR IATA
code. This type of code you find on your airplane tickets.

```{r get a METAR report with IATA code}
metar_get("EWR")
```

The above message is intended for professionals like pilots or air
traffic controllers. The first purpose of preparing the pmetar package
was the need of extracting wind speed and air pressure values from METAR
reports for some airports in Poland. Later the package functionality was
extended. We will go through the main functions with a historical METAR
report from John F. Kennedy International Airport.

## Downloading historical METAR weather report

The function *metar_get_historical()* allows to download METAR weather
reports for a defined period of time. The default online source of METAR
reports, *from = "iastate"* is the Iowa Environmental Mesonet web page
of Iowa State University ASOS-AWOS-METAR
<http://mesonet.agron.iastate.edu/AWOS/>.

```{r label = "get historical METAR reports from JFK", eval = FALSE}
dm <- metar_get_historical("JFK", start_date = "2020-06-27", end_date = "2020-06-29", from = "iastate")
```

```{r label = "create dm offline", echo = FALSE}
dm <- c("202006270000 METAR KJFK 270000Z AUTO 19007KT 10SM CLR 23/18 A2990 RMK T02300180 MADISHF",
        "202006270005 METAR KJFK 270005Z AUTO 19008KT 10SM CLR 24/18 A2990 RMK T02400180 MADISHF",
        "202006270010 METAR KJFK 270010Z AUTO 20008KT 10SM CLR 24/18 A2990 RMK T02400180 MADISHF",
        "202006270015 METAR KJFK 270015Z AUTO 21005KT 10SM FEW110 24/18 A2990 RMK T02400180 MADISHF",
        "202006270020 METAR KJFK 270020Z AUTO 21005KT 10SM SCT110 24/18 A2990 RMK T02400180 MADISHF",
        "202006270025 METAR KJFK 270025Z AUTO 23008KT 10SM SCT110 24/17 A2990 RMK T02400170 MADISHF")
```

```{r label = "show head of dm"}
head(dm)
```

The second backup source, *from = "ogimet"* is Weather Information
Service provided by Ogimet <http://www.ogimet.com/>. Please take into
consideration that Ogimet usually blocks too frequent requests for data
due to the server overload, the requested period is limited to 31 days
and for the most of airports METAR reports are available from the
beginning of the year 2005.

```{r, label = "example for Ogimet", eval = FALSE}
metar_get_historical("JFK", start_date = "2020-06-27", end_date = "2020-06-29", from = "ogimet")
```

In the package version from 0.4.0 it is possible to check the syntax of
downloaded METAR reports with the function *metar_is_correct()*. Also in
several functions the additional parameter *check* was implemented. The
default value is TRUE. If it is set to FALSE decoding of METAR reports
should work as in the previous package versions.

```{r checking the syntax of reports}
metar_is_correct(dm[1:5])
```

Let's one report with incorrect one and check how it works.

```{r adding one incorrect report}
dc <- c(dm[1:5],
        "202006261625 SPEC KJFK 261625Z AUTO 28009KT 10SM CLR 30/12 A2995 RMK T03000120")
metar_is_correct(dc)
```

It is possible to select incorrect reports from input.

```{r}
dc[!metar_is_correct(dc)]
```

The function has the parameter verbose which helps to identify incorrect
reports. The index and the incorrect METAR are displayed

```{r checking the syntax of reports with verbose}
metar_is_correct(dc, verbose = TRUE)
```

The check of syntax was implemented in the following functions, however
it must be enabled by setting *check = TRUE*. Only in the function
*metar_decode()* it is set to TRUE by default.

-   metar_decode()
-   metar_dew_point()
-   metar_dir()
-   metar_gust()
-   metar_pressure()
-   metar_speed()
-   metar_temp()

We will parse the last report from the above *dm*. In historical reports
dates and hours are placed at the beginning of texts. Normally it's
extracted and parsed, but for now let's remove it

```{r remove dates at the begining of reports}
(dm[length(dm)])
my_report <- substr(dm[length(dm)], 14, nchar(dm[length(dm)]))
my_report
```

It has to be noted that the report part after the RMK, remarks, is not
analyzed, except the temperature information, which is provide more
precisely in remarks.

## Decoding main informatin from a single METAR weather report

The first element **METAR** indicates the text consist of a METAR
weather report. If a report was issued under special circumstances, a
text SPECI replaces METAR.

### Airport

The second four letters element, **KJFK** identifies an airport from
which a METAR issued. We can extract it

```{r find airport}
metar_airport(my_report)
```

and find the **KJFK** geographical coordinates, elevation, airport IATA
code, airport name and source of information.

```{r find location}
metar_location(metar_airport(my_report))
```

### Day and time

The third element **282355Z** includes a day of a month, a time and a
time zone.

```{r find day time and zone}
metar_day(my_report)
metar_hour(my_report)
metar_time_zone(my_report)
```

The fourth element, in our case **AUTO** informs that a report was
generated automatically. If a report was manually corrected it is
**COR**. This element is not taken into consideration by the package
pmetar.

### Wind speed and wind direction

Next, there is the text **07007KT** where three first digits informs
about a wind direction in degrees. Two next digits are a wind speed and
the letters the end define units, here KT, hence a wind speed is in
knots.

```{r find dir and speed}
metar_dir(my_report)
metar_speed(my_report, metric = TRUE)
metar_speed(my_report, metric = FALSE)
```

The function *metar_speed()* reports a wind speed in m/s with the
default value of the parameter *metric = TRUE*, or in knots when *metric
= FALSE*.\
When a wind direction varies, a METAR report has additional component,
like **140V200**, which informs that a wind direction fluctuates from
140 to 200 degrees.

```{r variable direction}
variable_direction_METAR <- "EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG"
metar_dir(variable_direction_METAR)
```

In this case an output is character what can be useless for statistical
calculations. If only main direction in the numeric format is needed, it
is possible to set the parameter *numeric_only = TRUE*.

```{r numeric only variable}
metar_dir(variable_direction_METAR, numeric_only = TRUE)
```

### Visibility

The part **10SM** is the visibility. In this case it's 10 statue miles.
With the default value of the parameter *metric= TRUE* and *numeric_only
= FALSE* we get output in meters. For *metric = FALSE* in statute miles.

```{r find visibility}
metar_visibility(my_report, metric = TRUE)
metar_visibility(my_report, metric = FALSE)
```

When the visibility is described as CAVOK we have two options to decode
it

```{r find visibility CAVOK}
metar_visibility("201711271930 METAR LEMD 271930Z 02002KT CAVOK 04/M03 Q1025 NOSIG= NOSIG=")
metar_visibility("201711271930 METAR LEMD 271930Z 02002KT CAVOK 04/M03 Q1025 NOSIG= NOSIG=", numeric_only = TRUE)
```

When the visibility is described as for example P6SM we can decode in
two ways

```{r find visibility PdSM}
metar_visibility("200005120845 METAR METAR MMGL 120845Z 27005KT P6SM FEW230 18/04 A3012 RMK 00190 062 903", metric = FALSE)
metar_visibility("200005120845 METAR METAR MMGL 120845Z 27005KT P6SM FEW230 18/04 A3012 RMK 00190 062 903", metric = FALSE, numeric_only = TRUE)
```

### Weather conditions

The function *metar_wx_codes()* extracts and parses the below weather
conditions codes.\
In the package versions starting from 0.4.0 the parameter *sep* with the
default value ";" was introduce. It allows to avoid problems with saving
output in .csv files. Two values are allowed, comma and semicolon. If
you need to get the function output separated by commas just set *sep =
","*.

```{r weather condition codes}
metarWXcodes
```

In our METAR examples part **-RA** informs about weather conditions.

```{r find weather conditions}
metar_wx_codes(my_report)
```

This part of a METAR can be quite complex, like in the below example:

```{r}
metar_wx_codes("202002022205 METAR KEWR 022205Z AUTO 24008KT 6SM -RA -SN BR SCT006 BKN014 OVC024 02/01 A2954 RMK T00200010 MADISHF")
```

### Cloud coverage

Next part, **SCT028 SCT035 BKN079**, informs about a cloud coverage

```{r cloud coverage}
metar_cloud_coverage(my_report)
```

### Temperature and dew point

The temperature and the dew point can be extracted from two elements of
a METAR report, before the RMK remarks marker *23/20* which can be found
in the most reports. Or from the part after the RMK remarks marker
*T02300200*, more precise but not always available.\
The temperature is coded in Celsius degrees, here **23**/20, or more
detailed in T0**230**0200.

```{r find tempreature}
metar_temp(my_report)
```

If there is a letter M in the front of two digits, **M**23/00, or there
is a digit one after T, T**1**230, the temperature is below zero Celsius
degrees.\
The dew point can be decoded from the last two digits 23/**20**, or more
detailed from T02300**200**. Dew points below zero Celsius degrees are
decoded in the same method as above. For example 04/**M**03 or
T0039**1**033 mean that the dew point temperature is -3 Celsius degrees
or more precisely -3.3 Celsius degrees.

```{r find dew point}
metar_dew_point(my_report)
```

Here there is a report with the more precise temperature information in
the RMK remarks part.

```{r find temperature after RMK}
metar_temp("202001010851 METAR KEWR 010851Z 27010KT 10SM FEW030 BKN070 BKN100 BKN210 04/M03 A2969 RMK SLP054 T00391033 52012")
metar_dew_point("202001010851 METAR KEWR 010851Z 27010KT 10SM FEW030 BKN070 BKN100 BKN210 04/M03 A2969 RMK SLP054 T00391033 52012")
```

### Pressure

In our example a pressure value is coded in the **A2972** as inHg (inch
of mercury). With the default parameter *altimeter = FALSE*, the
function *metar_pressure()* returns a pressure in hPa.

```{r find pressure}
metar_pressure(my_report)
```

The pressure value can be also presented in a METAR report as **Q1008**,
already in hPa.

```{r find pressure hPa}
metar_pressure("EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG")
```

If a pressure is needed in inHg (inch of mercury), the parameter
*altimeter* has to be set to TRUE.

```{r find pressure inHg}
metar_pressure("EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG", altimeter = TRUE)
```

### Wind shear

Information about wind shear can be extracted with the use of the
function *metar_windshear()*.

```{r find wind shear}
metar_windshear("CYWG 172000Z 30015G25KT 3/4SM R36/4000FT/D -SN BLSN BKN008 OVC040 M05/M08 A2992 REFZRA WS RWY36 RMK SF5NS3 SLP134")
```

### Runway visibility

Information about runways visibility can be extracted with the use of
the function *metar_rwy_visibility()*, in meters.\
In the package versions starting from 0.4.0 the parameter *sep* with the
default value ";" was introduce. It allows to avoid problems with saving
output in .csv files. Two values are allowed, comma and semicolon. If
you need to get the function output separated by commas just set *sep =
","*.

```{r find runway visibility in m}
metar_rwy_visibility("CYWG 172000Z 30015G25KT 3/4SM R36/4000FT/D -SN BLSN BKN008 OVC040 M05/M08 A2992 REFZRA WS RWY36 RMK SF5NS3 SLP134")
```

or in feet

```{r find runway visibility in ft}
metar_rwy_visibility("CYWG 172000Z 30015G25KT 3/4SM R36/4000FT/D -SN BLSN BKN008 OVC040 M05/M08 A2992 REFZRA WS RWY36 RMK SF5NS3 SLP134",
                     metric = FALSE)
```

## Putting all together

### Decoding METAR reports

Let's come back to our dm list with historical METAR reports downloaded
at the top of this document. Please notice that in all rows there are
dates and hours in the front of METAR reports. It will be parsed and
placed in the column *METAR_Date* below.

```{r}
head(dm)
```

Now we can decode all elements and place them in the tibble. It is
possible to choose between Metric (the default *metric =* TRUE) or
Imperial (*metric =* FALSE) systems. Pressure values can be decoded in
hPa (the default *altimeter =* FALSE) or in mmHg (*altimeter =* TRUE).\
In the package versions starting from 0.4.0 the parameter *sep* with the
default value ";" was introduce. It allows to avoid problems with saving
output in .csv files. Two values are allowed, comma and semicolon. If
you need to get the function output separated by commas just set *sep =
","*. Also the parameter check with the default values TRUE was added.
It allows to handle errors when the function is not able to decode METAR
reports.

```{r decode metars}
decoded_metars <- metar_decode(dm)
```

The following columns were created:

```{r columns names}
names(decoded_metars)
```

First rows of the tibble with decoded METAR reports:

```{r}
print.data.frame(head(decoded_metars))
```

Let's take a look how the function handles the input data with one
erroneous report.

```{r handling incorrect reports}
metar_decode(dc)
```

The parameter check can set to FALSE and some values from incorrect
reports can decoded. However the function can fail.

### Decoding one METAR report with the function *metar_print()*

The function *metar_print()* it is possible to decode one report and
display main parameters

```{r example of metar_print}
metar_print(dm[1])
```
