::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact

Timestamp range in gnuplot

June 20th, 2011
gnuplot, tech  [html]
In gnuplot, you might have some data you'd like to graph that has timestamps:
     1308369601 0.15
     1308369661 0.05
     1308369721 0.43
     1308369781 0.41
     ...
  
You can see many places that to tell gnuplot your xaxis is in seconds since the epoch you use:
     set xdata time
     set timefmt "%s"
     set format x "%H:%M"     # or anything else
     set xlabel "time"
  
If you want to limit the range, you might think you could do something like:
     set xrange [1308369932:1308373241]
  
If you try this, you'll get an error like:
     "plot.gnp", line 16: all points y value undefined!
  
To fix this, you need to subtract 946684800 from the start and end of your xrange:
     set xrange [1308369932-946684800:1308373241-946684800]
  
What is going on here? It turns out that unlike everything sensible in the unix world, gnuplot calculates time in seconds since the beginning of the year 2000 instead of the year 1970. So it interprets [1308369932:1308373241] as early morning 2041-06-17 instead of early morning 2011-06-18. The magic number, 946684800, is the number of seconds between 2000-01-01 and 1970-01-01.

I understand gnuplot was trying to be platform independent, but it's pretty annoying now that the 1970 epoch has become dominant.

Recent posts on blogs I like:

Incoming Gantz-Led Government to Invest in Israel’s Infrastructure

Israel’s incoming prime minister Benny Gantz unveiled an emergency government, to take power following an upcoming confidence vote in the Knesset. The last two MKs required to give Gantz a 61-59 majority, two members of Gantz’s own Blue and White Party wh…

via Pedestrian Observations April 1, 2020

Finding home in the time of coronavirus

Disclaimer: I’m going to say this once. Obviously, I am not happy about the coronavirus’s threat to public health or the economic toll it’s taking. I do not think the existence of this pandemic is good. Just so happens that social distancing and remote wo…

via Holly Elmore March 31, 2020

Massachusetts should shut down immediately

We’ve been running 30x fewer tests than other states, and have been extremely tardy in responding to the Biogen outbreak.

via benkuhn.net March 15, 2020

more     (via openring)

More Posts:


  ::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact