I ‘m still interested in a working Zimmerman algorithm and investigated a little bit more the Weather Underground changes. A web search showed that they have not only discontinued their free API key. They have also stopped pulling data from Netatmo weather stations since the end of the day of 24-May-2018. At least no European Netatmo station seemed to be anymore listed in their Wundermap. The reason for this might be the EU General Data Protection Regulation that is being enforced on 25-May-2018. However, no official statement is given by Weather Underground and it is not clear if they provide this service again?
Looking at Netamo, they are still providing the data and the corresponding API interface:
https://www.netatmo.com/site/connect/program
However, Netatmo forum questions and answers show they don’t feel responsible for the situation and are maybe just waiting for another weather service to use their data?
This causes the problem that e.g. my Netatmo weather station can’t currently be used as data source for the OpenSprinkler Zimmerman algorithm. Entering my home location leads to a nearby private weather station, that probably has less quality in case of temperature, humidity and working rain gauge measurements. I have tried to change the location, which is only possible if I click on Location to open a map, search, locate, and select a different address.
After all, retrieving weather data for a working weather controlled sprinkler system seems to be not an easy task. I hope that the OpenSprinkler changes to OWM can improve the situation and maybe OWM is willing to use Netatmo data in the future?