Getting my pollen forecast into Home Assistant
As someone who is affected by various plants' pollen, knowing in advance how bad it's going to be helps planning the day and anticipate allergy-related malady.
My country's meteorological service publishes pollen forecasts on their website, including per-state maps. It has become a ritual to visit their site every morning to check out the updated forecast, which is slightly inconvenient.
The forecast map is an image with a dynamic URL that is updated daily, so to get this into the Home Assistant dashboard, I need something that:
- Fetches a remote image.
- Supports URL templating (to build that dynamic URL).
- Caches it to avoid spamming the service with redundant requests.
- Shows up as a plain image on the Home Assistant dashboard.
The dynamic URL has a static prefix, followed by /<state name>/<year><month><day><plant name>.
For my purposes, <state name> and <plant name> are static enough, so I only need to template the date.
Solution
Surprisingly, the camera integration fits the bill perfectly, as simply as that:
camera:
- platform: generic
name: Birch pollen load today
still_image_url: https://www.zamg.ac.at/zamgrastergfx/gfx/pollen/salzburg/{{ now().year }}{{ now().month }}{{ now().day }}birke
The image is fetched once and cached for as long as the URL remains the same, resulting in clean 24 hour caching and maximum grace.
As this creates a camera entity, any dashboard widget supporting cameras can be used, which makes showing the image easy.
To spruce things up a little, I'm also displaying the latest measurements from my particulate matter sensors.
Future potential
Most of the year, I don't care, so calendar based visibility in the dashboard would be neat.
Even better would be visibility that's based on whether there is any pollen activity. That could work by generating a color histogram of the image and counting the pollen-indicating pixels.
Such analysis could also be used for alerting.