Q: No daylight saving in waveform chart

[Dols]

Hello,

I'm lost:
I have a large logfile (couple of years) and i wan't to display this
with labview. The times i use are labview timestamps (seconds since 1
januari 1904 0:00 utc). Problem is when i plot them in a chart it
displays them in my local time zone (amsterdam).

Is there a possibility to plot these data in an chart in UTC without
Daylight saving time? Most preferable without changing the timezone in
windows, but even then a UTC timezone without DST doesn't exist.

Any help???

many thankx,
Richard Dols

[Greg_McKaskle2]

> Is there a possibility to plot these data in an chart in UTC without
> Daylight saving time? Most preferable without changing the timezone in
> windows, but even then a UTC timezone without DST doesn't exist.
>

Try setting the X Offset either programmatically or using the Formatting
or property pages. Basically, this will add a given offset to the
points being labeled on the scale without touching the data on the
graph/chart. Compute the difference between how the data was stored and
where it is being viewed in seconds and set the offset to the negation
of that difference. Adjust if this is in the wrong direction or is off
by an hour due to daylight savings, etc.

Greg McKaskle

[waldemar.hersacher]

Dear Greg,

I have never tested this and none of my customers called me about the following problem:

What happens if the logging runs to the time where daylight saving is on or off? In March the local time jumps from 2:00 to 3:00 and in October it jumps from 3:00 to 2:00 giving two hours from 2:00A to 3:00A and from 2:00B to 3:00B. The numbering A and B is the rule used in Germany for the "document of birth" (Geburtsurkunde).

Would this cause any confusion in the x-axis of a chart or graph?

Waldemar

[Greg_McKaskle2]

> I have never tested this and none of my customers called me about the
> following problem:
>
> What happens if the logging runs to the time where daylight saving is
> on or off? In March the local time jumps from 2:00 to 3:00 and in
> October it jumps from 3:00 to 2:00 giving two hours from 2:00A to
> 3:00A and from 2:00B to 3:00B. The numbering A and B is the rule used
> in Germany for the "document of birth" (Geburtsurkunde).
>
> Would this cause any confusion in the x-axis of a chart or graph?
>

Daylight savings in general causes confusion. I'm not certain that it
actually accomplishes anything positive anymore. But to your question,
what will happen when it changes?

This is all subject to change, either by us or the OS, but at t
he moment
LV uses OS libraries for turning a timestamp into a string. The current
behavior of those libraries is that all of the times, historical or
current will shift by one hour. It is very difficult for a computer to
determine whether the timestamp falls in an A or B period. Sure it can
be done, and I believe some Unix servers do it, but in general, everyone
does UTC internally and then uses the current time zone to adjust the
UTC, then determines whether DST is currently in effect, then turns that
number into a string.

I believe this means that if you are at work at 2:00 in the morning,
that you will get another 2:00 an hour later on the chart, but as soon
as the historical values scroll off the screen, all the previous values
will be labeled 12:00 1:00 2:00.

As I said, DST complicates everything and someone might change this
behavior in a future OS or a future LV.

Greg McKaskle