hexalog / libklio normalize readings to minute-resolution

[gonium]

NOTE: This was originally submitted here: mysmartgrid/hexabus#107

Hi,

I would like to record multiple devices in the house with HexaBus plugs+ and plot a sum graph with a minute resolution. The fact that each plug submits its readings at different seconds is not quite good for this use case. My quick and dirty workaround was:

• just cut off split seconds of timestamp
• look at the 5 values before and after the current value to see if there's another reading for the same minute
• average over values of the same minute

Of course, it would be even better to calculate a more accurate minute value by taking the last value before and the first after the minute in question.
E.g., if you had readings (UNIX timestamp here converted to human-readable datetime)

datetime value
2012-10-01 19:59:40 50
2012-10-01 20:00:30 100
2012-10-01 20:01:10 200

1. imagine a line through the points (2012-10-01 19:59:40;50) and (2012-10-01 20:00:30;100) which could also be referred to by (-20;50) and (30;100) when counting the seconds to the next full minute (full minute = 0)
2. the linear equation has the form y = ax + b
3. the gradient of the line through the two points is a = (100-50)/((30-(-20)) = 50/50 = 1
4. with the point (-20;50) you get b=70

do the same with the next two timestamps (-30;100) and (10;200), you get a = 2,5 and b = 175

That way, the normalized readings would read:

datetime value
2012-10-01 20:00:00 70
2012-10-01 20:01:00 175

Could we have this calculation in libklio?

Cheers,

Monika