I see ground truth, as with many problems, as a matter of scale. The rough (OLED TV!) and the smooth (a single LED bulb?).
Mandelbrot (and Slartibartfast on some level) cited the impossibility of measuring the “ground truth” coastline of Norway. Beyond the method, it’s a matter of the measurement scale. Beyond the scale it’s a matter of the measurement method.
Having just read Thermodynamic Weirdness, I also think of Rudolf Clausius’s seminal papers on thermodynamics and the intertwined definitions of system, state, and boundary. From a ground-truth energy perspective, boundary quickly devolves into Heisenberg territory: uncertainty.
That said, Sense device detection (vs. absolute energy integration) ground truth is also a matter of scale:
-
At the highest level = “is it on/off?”
-
Mid-level = “roughly” how much energy is it using during a certain period T, where T is as small as possible.
-
Low-level = looking at successive T periods, is there sufficient information to disaggregate devices? This feeds back to #2 and leads to the refinement of T. Zoom in/zoom out. Of course the instantaneous state (V/A/phase/frequency) matters a lot for complex real-world scenarios but theoretically, with sufficient resolution, you can always disaggregate in some cases (many) and never (perhaps) disaggregate in others … this feeds back to #1.
For #1, you don’t need to care about actually power, you are just concerned with “is it on or off”. There is also the possibility of ground truth by a process of elimination:
This is certainly not the best illustration, but as I posted elsewhere I think smartplugs are tracking usage well enough and closely enough to Sense’s ground truth input (the CTs + wires) that the combined systems lead to more information. An interesting feature of these waveforms is that the mis-calibration (wrong absolute power) doesn’t necessarily matter for disaggregation … in fact you can see that the timing is very precise and this speaks to @kevin1’s #3.
