How to set the time and date for terminator display?

i have a week of hourly ham radio data.

How may I set the gmt solar to position the datkens and terminator on the globe

As I progress through the day my terminator doesnt change.

Here is my animation, I wish to have the night/day rotate around the globe


And be able to see how the presentation is actually changed by the position of the sun.

Would need to see your script and data to determine what is wrong

Thanks, here is my bash script

pi@pi-OptiPlex-9020:~/SQL/w1hd$ cat

echo $1

gmt begin $1 png

Iparam=$(echo -I-104/40+d2023-11-18T$(echo $1 | cut -c2,3):00) # neat text out

gmt coast -Rg -JG255/40/6i -Bag -Dc -A5000 -Gwhite -SLightBlue #india

echo gmt solar -W1p -Tdc -Gblack@87 $Iparam. # the iparam prints cool solar text.

gmt solar -W1p -Tdc -Gblack@87 # $Iparam just puts out text solar data

gmt plot -Wthickest,red -Fr-105/40 $1

gmt plot -Ss0.5c -Gred -Wthinnest $1

echo “-105. 40.” | gmt plot -Sa0.5c -Gblue -Wthin

gmt end show

killall eog # this works to not display the image, A better way??? Crummy but works!

convert $1.png W1HD.10m.jpg -geometry +10+10 -composite temp2.png

convert temp2.png -font URWBookman-Demi -pointsize 134 -gravity southwest -annotate +10+10 $1 outfull.png

convert outfull.png -resize 44% $1.png

rm -f outfull.png temp2.png

#timeout 15 display outsmall.png # remove from bash script


pi@pi-OptiPlex-9020:~/SQL/w1hd$ cat h22.txt

-91.875 37.271 K6RFT


RUN AS ./ h22.txt

I get a great terminator with local time. I need to set the data time to set the terminator for days ago, at a particular hour of the day.

How do i input the time date to have the display png match the time the data was taken.

There has to be a time date input. I could change the system date/time. I am certain GMT has a proper way to do this. The terminator is just super on local time.

Thanks, Bradshaw

Well, since you add “show” to gmt end you are asking for the graphics to be displayed. If you dont want that, why add show?

Looks like your cut -c2,3 pulls out 91 from your h22.txt file and thus your dateTclock string is 2023-11-18T91 which is not recognised since 91 exceeds 24.

If this is meant to make a frame in a movie then I will give my last recommendation to use movie/events, but make it as difficult as you please, of course.

the cut, cuts the two digit hour from my data file. and the annotate from imagemagick displays it just fine.

I an brand new here, using examples, not knowing what I am doing, but meeting with amazing success from the excellent examples. I WILL REMOVE THE SHOW.

GMT beautifully creates the terminator for the current local system time.

How may I specify the date time that I want the terminator to display as?

   Again, a simple new guy confusion. and extensive search in the docs 

and google hasnt let me to the answer. I really appreciate the help here in t
he lounge. Nice music too! Kudos’ to the pianist.

It’s my goal, entering the date time (any format) into the bash gmt script to get the terminator and darkness rotating around the globe. Rotating darkness, very philosophical.

THanks for the hint about “show”


GMT follows ISO8601 for dateTtime stamps.

thanks for the help. your examples are so powerful that that is my main path.

I will use the GMT reccomended movie soon, for now I am using my 25 year old assemble png into an animated gif, piggy, wasteful, but instant “old” success.

I greatly appreciate your help. tnx!

how do I tell gmt so render the terminator for

       2023-11-11T03:00:00 UTC

             Each of my datapoints is extracted from 
            6.48 billion record reception log with an epoch date time 
            to the epoch second. for the 2 minute transmission

            I wish to have the terminator aligned with that old epoch time.

           I dont know how to tell gmt the time to render.


From the man page it seems you have to pass your ISO8601 string via the +d modifier to -T, no?

perfect thank you.

I generate the ISO date-time from the epoch (in UTC)


                    should do it, thanks for the novice guy help!

from the manual
-Tdcna[+d date][+z TZ]

Plot (or dump; see -M) one or more terminators defined via the dcna flags. Where: d means day/night terminator; c means civil twilight; n means nautical twilight; a means astronomical twilight. Add +d date in ISO format, e.g, +d 2000-04-25T12:15:00 to know where the day-night was at that date [Default is now]. If necessary, append time zone via +z TZ.



Thank you for the great help

the data is goofed up, my time for data collection is reversed, BUT THE MECHANICS are now perfect!

the goal, when the data is resolved is to see how night / day / twilight affect radio signals on different bands and times of year (and sunspots). this is the perfect tool!


Glad you got it working!

Ham radio is cool.
Please share results with us, if you can and want!

Interested too ! :slight_smile: