Is it possible to modify a past value in rrdj4 persistence? (Correct time delay of external temperature in charts)

Setup, Configuration and Use Items & Sitemaps
1

I’m monitoring the temperature measured in my small greenhouse and I am comparing it with the current temperature as obtained by the the weather binding. I am using the rrd4j persistence. I noticed that the Current temperature given by the weather binding is delayed by at least a couple of hours: i.e. I would need to shift the binding temperature to the left of the chart by a couple of hours.

This means that the value recorded say at 12.00 is actually referring to 10.00: therefore I would need to modify the value taken two hours before.

Would this rule work ?

rule "correct delay"
when 
   Item Temperature changed
then
   Temperature_adjusted.historicState(now.minusHours(2)).state=Temperature.state
end

Temperature and Temperature_adjusted are two number items, which are also persisted with rrdj4

Thanks for your help,
Lionello Marrelli

2

I am afraid but you cannot edit rrd4j databases from the rules DSL
I have read of ways to do it other wise:

3

Thank you for your reply, but this is useful for one time modifications.
Probably InfluxDB and Grafana need to be used.

4

Not sure why you want to modify the database? You’ve found the method you could use to fetch the greenhouse data from two hours ago and compare it with the ‘delayed nowcast’. What else is needed?

It might be worth exploring other weather providers to see if something more accurate is available for your locality.

5

You are right, I can delay my sensor data: the drawback is that the chart will be 2 hours late.

6

Okay, you’re graphing it. So it’s really just a case of relabeling the time axis? I don’t know Grafana or if it can do that, seems feasible.

I must say, I’d be considering an exterior temp sensor … wouldn’t that help with greenhouse management as well?

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