README.md: add more FAQ #90

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Starfish merged 2 commits from arwagner/TinyWeatherForecastGermany:1_EnhanceReadme into master 4 months ago
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README.md

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Tiny Weather Forecast Germany
Tiny Weather Forecast Germany
=================================
Weather forecast with widgets for up to 10 days, based on open data from the Deutscher Wetterdienst (DWD).
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FAQ
---
*For locations in a different time zone the day/night icons seem incorrect.*
### For locations in a different time zone the day/night icons seem incorrect.
The app always displays the date & time of your device (and locale). Example: you are in Berlin and have selected the weater for Cuba. The app shows you the weather in Cuba at the corresponding Berlin time and uses the day/night-icons corresponding to the Berlin time. Once you have travelled to Cuba and your device switched to the local time in Cuba, the app will display the weather in Cuba at the Cuba time.
*How to read the widget?*
### How to read the widget?
The widget icon, the weather description and the current temperature refer to the weather forecast that can be expected until the next full hour. The low and high temperatures refer to the values that can be expected to occur from now to midnight.
When showing more days (bold widget, large widget), the min and max values and the weather symbol refer to the whole day.
*What do the symbols in the main app mean?*
### What do the symbols in the main app mean?
Symbols used:
<img src="app/src/main/res/mipmap-mdpi/symbol_precipitation.png" height="16" width="16"/> precipitation
@ -173,37 +173,106 @@ Symbols used:
<img src="app/src/main/res/mipmap-mdpi/symbol_fog.png" height="16" width="16"/> fog
<img src="app/src/main/res/mipmap-mdpi/symbol_drizzle.png" height="16" width="16"/> drizzle
<img src="app/src/main/res/mipmap-mdpi/arrow.png" height="16" width="16"/> wind direction
### What do the icons show do?
You may get a hint about their functionality if you just _long-press_ them.
*My widgets don't get updated (unless I open the app).*
### My widgets don't get updated (unless I open the app).
The widgets get updated every 15-30 minutes. If this does not happen at all or only happens when you open the app, then you likely have a device that prefers battery life over proper functionality. Likely, some so-called *battery saving feature* kills the components of the app and breaks the updates. See [this page](https://dontkillmyapp.com/) to ckeck if you own such a device and what you can do.
*How often does the app update the weather forecast?*
### How often does the app update the weather forecast?
The Deutscher Wetterdienst updates the forecast data that is used every 6 hours. Therefore, it does not make sense to pull weather data more frequently than this from the DWD API. However, a manual data update triggered by the user's selection in the main app always forces an update of forecast data. The forecast data covers the next ten days. So it is pretty feasible to present a weather forecast for some time without polling new data.
*How often does the GadgetBridge app gets updated (when this feature is enabled)?*
### How often does the GadgetBridge app gets updated (when this feature is enabled)?
When GadgetBridge support is **enabled**, the app will, in the best case, update GadgetBridge every 30 minutes using forecast data that is already in place, meaning that the DWD API will not be called for this. However, on devices with API 23 or higher, such updates might not occur that regularly when the device goes in *doze mode*, but should be launched in the so-called “maintenance window”, and it is difficult to say what this really means in manners of time. This will likely mean very different things depending on the device and/or ROM.
If you encounter problems with GadgetBridge not updating, placing the widget on the home screen may help, since the widget will try to also update GadgetBridge every time the widget itself gets updated by the system.
*Why is percipitation displayed in kg/m² instead of cm?*
### Why is percipitation displayed in kg/m² instead of cm?
Because the DWD provides this data this way. This cannot be changed. Please consider that this unit is more precise regarding the amount of hail and snow.
*Why does the app not display sunrise und sunset?*
### Why does the app not display sunrise und sunset?
Sunrise and sunset cannot be reliably calculated with the formulas used for latitudes < -65° and > 65°. When this is the case, this feature is disabled.
*Why does the app show a particular weather icon (and not an other)?*
### Why does the app show a particular weather icon (and not an other)?
Icons refer to *significant weather conditions*. The idea is to show you the most important (significant) weather condition that you can expect to occur within the given time period. For example, thunderstorms have a higher priority than rain and rain/fog have a higher priority than clouds. If such a significant weather condition is likely to occur, it will be preferred over others.
Usually, the weather conditions are calculated by the DWD. If a weather condition is not available in the forecast data, the app tries to calculate it from other items. If you are interested how this app calculates icons in this case, see [here](https://codeberg.org/Starfish/TinyWeatherForecastGermany/src/branch/master/app/src/main/java/de/kaffeemitkoffein/tinyweatherforecastgermany/WeatherCodeContract.java) in the source code.
Usually, the weather conditions are _calculated by the DWD_. If a weather condition is not available in the forecast data, the app tries to calculate it from other items. If you are interested how this app calculates icons in this case, see [here](https://codeberg.org/Starfish/TinyWeatherForecastGermany/src/branch/master/app/src/main/java/de/kaffeemitkoffein/tinyweatherforecastgermany/WeatherCodeContract.java) in the source code.
Thresholds for significant weather conditions are subjective and perhaps debatable, but weather conditions calculated by the DWD have priority and always remain unmodified, if available. If you are interested in the priorities, see [this DWD document](https://www.dwd.de/DE/leistungen/opendata/help/schluessel_datenformate/kml/mosmix_element_weather_xls.xlsx?__blob=publicationFile&v=6).
### Why does the app give a different value for some parameter (e.g. temperature) than the official station reading?
TWFG gives _forecasts_, not the current reading at some weather station. If the displayed value in TWFG differs from an official reading at some spot, the forecast was just off.
### Where do the names come from that are offered in searches?
TWFG uses _WarncellIDs_ for the regions offered. These are closely related to the [Amtlicher Gemeindeschlüssel](https://www.destatis.de/DE/Themen/Laender-Regionen/Regionales/Gemeindeverzeichnis/_inhalt.html) (AGS) provided by destatis. Basically, the WarncellIDs are an extension of the AGS. WarncellIDs also feature human-readable names (e.g. "Landkreis Göttingen"). These names can be used while looking for a weather station. They _do not_ refer to the names of weather stations. Once you select a name the app will give you a list of close by stations including their distance to choose from. This distance is derived from the center of the area polygon(s) associated with a given region. It may happen, that a WarncellID has more than one search key associated. E.g. searching for `Insel Helgoland` or `Gemeinde Helgoland` will show a list starting with `Helgoland` at an approximate distance of 0.4 km. Hence the weather station is actually just called `Helgoland`.
*Note* more than one station will be shown if your search matches a search key. These stations are sorted by increasing distance from the initially searched entity. E.g. searching for `Insel Helgoland` in the above example will also show `Elbmuendung` (a sea area next to Cuxhaven) which is 23.4 km away, `UFS Deutsche Bucht` (an automatized weather station aboard a light vessel in the middle of the German Bight) already 29.3 km away, or `Wangerooge` (one of the East Frisian islands) at a distance of 29.4 km. (And of course many others even further away.) If `Helgoland` is searched however, it matches the station right away, and the app jumps to it immediately without a further selection.
### Is there a map available to choose a spot if I don't know the proper names in the vicinity?
You can use any application on your device that allows to share coordinates via `geo:`-intents to TWFG. Most mapping and location applications will allow this.
This also works from a web browser, provided the page in question offers a `geo:` link. [geohack](https://geohack.toolforge.org) is a common service that provides such links as `Geo URI` (e.g. for [Helgoland](https://geohack.toolforge.org/geohack.php?pagename=Helgoland&language=de&params=54.1825_N_7.8852777777778_E_region:DE-SH_type:city(1307))). You may want to note that also Wikipedia links to this service once you click on the geographic coordinates in their web pages. (However, they do not provide a direct `geo:` link, yet.)
### Why does the delete icon next to the location not remove the selected location?
The delete icon works the other way around: it does not remove the currently displayed region but _all other_ regions that were selected at some point in the past. The idea of TWFG is centred around the idea of your usual location and not so much on a list of bookmarks.
### How do I delete a location?
Select your new region and hit the clean button next to the regions title. Mind that this will clean _all other_ regions, except the one currently displayed.
### Why does the app not update a location? It is in my bookmarks.
TWFG tries to be very conservative with your data volume. For this reason it only updates the currently displayed region. All other regions in the regions drop down are merely places once visited and do not get any updates.
*Note* the currently selected region is also the region displayed in any widget added to the home screen.
### How do I set the region to be displayed at the home screen widget?
Just select it as current region in the app. The region displayed in the app and in the widget stay in sync all the time. Any region change in the app is reflected in the widget(s) automatically.
### How can I fetch weather for a different location if I go on travel?
If you want to update a different location e.g. before travelling, select it first and update the data. (If `Always update` is not set you may do this manually.) You can then revert to your standard location. TWFG will remove data only once it got invalid over time, but keep all fetched data in it's internal cache.
### Why do some coloured ploygons show up next to the coasts sometimes?
Those stem from coastal or sea area warnings issued by DWD in their shipping forecasts. The warning areas correspond to the coastal and sea areas in those reports. The definitions of the sea areas can be found in the document "Sturmwarnungen und Seewetterberichte für die Sport- und Küstenschifffahrt" published regularly by DWD or "Wetter- und Warnfunk" updated yearly by the Bundesamt für Seeschifffahrt und Hydrographie (BSH).
*Note* there is a coastal area that stretches along the Elbe from Cuxhaven to Hamburg.
### Which weather model is the app using?
The app uses the *MOSMIX* model provided by Deutscher Wetterdienst (DWD). "The MOSMIX System of Deutscher Wetterdienst optimizes and interprets the computations of the numerical models ICON and IFS (ECMWF) and combines them to statistically optimal weather forecasts." (DWD). This model provides data for almost all common meteorological parameters and uses statistical methods to derive parameters not available in the numerical models. More details can be found at [the MOSMIX page at Deutscher Wetterdienst (DWD)](https://www.dwd.de/EN/research/weatherforecasting/met_applications/nwp_applications/mosmix_application_node.html)
### Can I access textual/specialized weather reports?
TWFG offers an extensive list of textual weather reports as provided by DWD. Those include short and medium term synoptic reports as well as specialized reports for the coastal regions of Germany, the sea weather bulletin for the North- and Baltic sea and the Mediterranean. Strong wind, gale and storm warnings are available for the German Bight, western and southern Baltic. *Note* Keep in mind that TWFG uses the data from DWD, so some textual reports are available in German only and the textual reports cover mainly Germany.
*Note* the textual sea and coastal weather reports coincide with those published by DWD via [RTTY radio broadcasts](https://www.dwd.de/EN/specialusers/shipping/broadcast_en/_node.html) but are drawn from the OpenData-server.
### What does wind direction "Beaufort" do? The wind speed still displays in another unit.
Setting the wind direction to Beaufort will display the wind as in a weather map with proper feathering according to the Beaufort scale, but it only affects the symbol used to display the wind direction. To set the unit used for wind speed to Beaufort use the appropriate setting in "Wind speed".
*Hint* setting the wind speed e.g. to knots and the display to `Beaufort` might be a good way to learn the Beaufort scale.
### What does the small arc next to the wind display refer to?
It shows the direction of the wind change during the next `Wind forecast period`. E.g. if the wind comes from the south and there is a quarter of an arc to the right next to it and the `forecast period` is set to 6h the wind will veer from S to E in the next 6 hours.
Contributing
------------

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