+++
date = 2024-10-19T20:02:17+02:00
title = "Night-time icons for Plasma's DWD backend"

[taxonomies]
tags = ["kde"]

[extra]
related = []
+++

For a couple of weeks now I have been using Plasma's built-in weather report
system. It supports various different sources for weather observations and
forecasts, one of which is my preferred service, [Deutscher
Wetterdienst](https://www.dwd.de) (DWD). Once the report location is set up, Plasma
displays the current conditions in the tray - clicking on it gives you an
overview of the next 7 days.

I've been quite pleased with this; a quick glance at the icon tells you
everything you need to know and the forecast is only one click away. It even
supports DWD's official warning system. There is one small problem with the tray
icon, however. See if you can spot it:

{{ img(path="icon-day.png", format="png", alt="A screenshot of Plasma's tray
showing a clipboard icon, a media control icon, and a weather icon. The weather
icon is displaying a sun with few clouds in front. The tray is also showing the
time. It is 23:57.", caption="Something's not quite right...") }}

That's right, I couldn't have possibly taken this image given this post's
timestamp is before 23:57! Good catch. More importantly, however, the icon is
showing the sun when realistically it's going to be dark outside. This has been
annoying me to no end, so a couple of days ago I decided to fix it.

Since Plasma already comes with weather icons suited for night-time use, I
really only needed a reliable way to tell when to switch to those. After some
spelunking in DWD's [two](https://dwd.api.bund.dev/)
[APIs](https://listed.to/@DieSieben/7851/api-des-deutschen-wetterdienstes), I
found that the latter contains sunrise and sunset times for its forecast
endpoint. The weather report system was already using this endpoint to fetch
forecast data, so it was a rather simple lookup of two values in the API and
then comparing the current observation time to those.

So, after some preparatory work to make date parsing more robust, I sent a
[merge
request](https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/4848)
upstream which was promptly approved and merged. Finally I could rest easy after
dusk, not having to worry about a sun chasing me around.

{{ img(path="icon-night.png", format="png", alt="A screenshot of Plasma's tray
showing a clipboard icon, a media control icon, and a weather icon. The weather
icon is displaying a crescent moon with few clouds in front. The tray is also
showing the time. It is 18:57.", caption="... much better!") }}

There's some more stuff that could be improved in the DWD backend, like station
availability. As far as I can tell, when using the open API, DWD limits access
to weather data depending on whether or not they have the full rights to it. The
API might therefore simply deny access to a station even though it is listed in
in [the official index](https://www.dwd.de/DE/leistungen/klimadatendeutschland/statliste/statlex_html.html?view=nasPublication&nn=16102).
There's no way to find out which station is accessible except to try them all.
To get around this, the DWD backend uses a [very simple
heuristic](https://invent.kde.org/plasma/plasma-workspace/-/blob/69a52cd6fbde80b087f59a633b4ff216c27ddff0/dataengines/weather/ions/dwd/ion_dwd.cpp#L396-403)
based on the first digit of the station ID, since all stations starting with 0
or 1 seem to work. However, this ignores a number of other, still accessible,
stations.

I'm planning to look into this further, hopefully finding a better solution so
that users of the DWD backend have access to as many stations as possible.