Why does Analaysis Period have a 1 hour offset?

[edpmay]

I am trying to align some calculations, and getting tripped up by the way Ladybug handles analysis-periods relative to the EPW data?

Scenario:

If I have some normal EPW data:

and if I apply an analysis period of 1 day (Jan 1), I would expect to get the values in the EPW for day 1 (for instance, for dew-point, in the example here shown here, staring at the value of ‘-2.8’):

but instead it is ‘offset’ by 1 hour. Meaning: the first value it returns is actually hour 8760, and it ‘dops’ the line for hour “1996, 1, 1, 24,…”:

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So is ladybug’s analysis period always ‘offsetting’ the data by 1 hour like this? I find that confusing as it does not align to the dates listed in the EPW file?

Or am I supposed to be handling the analysis period differently somehow?

I would have expected to just get all of the lines with the 1/1 date?

best,
@edpmay

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Example:

example.gh (23.7 KB)

[XiAO]

I also meet this issue recently.

I use the data from the Photovoltaic Geographical Information System (PVGIS) of European Commission.

I choosed one hour, which is on the PVGIS site for example 12, it will apears on the detailed pdf sheet (generated by PVGIS site) as 11:45, in grasshopper with ladybug it will be 11.

Curious about whether it is a general rule, since grasshopper starts with 0 instead of 1 in its counting system.