Hey all! For a christmas present I set up a weewx instance running on a rasberry pi for my father-in-law. He is using a KlimaLogg Pro station for a while with all 8 additional sensors in use. Up until now he used a self-created excel sheet, where he imported the data using the windows software of the KlimaLogg. In this excel sheet he implemented a formula to calculate the Saturation Vapor Density and the Actual Vapor Density (SVD & AVD) to get the actual amount of water in the air (in g/m^3). With this information he decides wether he has to air his rooms.
Now he really would like to have this information available somehow at the HTML report page created by weewx. (I guess the dewpoint is probably providing more or less the same information, but he seems to be quite proud of his formula). So I started to look into possible ways of doing this and would be interested in more professional opinions. First idea: I considered to just replace the formula to calculate the heatindex in bin/weewx/wxformulas.py. This would probably be the easiest way for me since he is not interested in the actual heat index and I would only have to change 1-2 lines of python code (and some configs to re-label the heatindex). But of course this could get complicated to maintain with future upgrades of weewx itself. Second idea: Making use of the user/ folder to place the custom functions in there. But I am a bit of a loss here of how to actually hook it up properly. My original plan was to extend the database by additional columns similar to heatindex and dewpoint but it does not seem to be too trivial nor do I really fully grasped how weewx works on the internal level to feel confident about this change for now. Third idea: I also read the "Defining new tags" section on the customization guide which sounded promising by using the Cheetah template enginge. I wouldn't have the data in the database but I wouldn't mind that too much. The two examples listed in the guides were all about aggregating existing information in a different way, so I am not exactly sure if I could also use this approach to basically derive a new number for every datapoint read out of the database? Fourth idea: Instead of modifying the core files I considered extending the klimalogg python module by basically extending the section where the interaction for the dewpoint and heatindex calculations happen by a third calculation. But again this might get complicated with future updates of the klimalogg driver and the klimalogg driver already seems to make heavy use of re-labeling existing observables to support all 9 sensors for each temperature and humidity and adding 9 more seems to be problematic at first glance. Fifth and final idea: It seems like I could also generate a PHP file instead of a HTML file, so I could just do all my db calls and calculations as some kind of post-processing happening after weewx and cheetah do their work. So what do the experts think? eddy
