tickinterval erratic behavior in axes with time data

[steppenwolf]

It's not clear to me how the tickinterval keyword works on axes with time data. In the two axes plots attached, I have set

    date_label = label_date(date_format=['%N-%D-%Y'])

In the first axis (1.png), I set xtickinterval = 10, intending for the major ticks to be ten days apart. No success.

In the second axis (2.png), I set xtickinterval = 5, intending the major ticks to be five days apart. This seems to work.

Any help with what's going on would be appreciated.

[steppenwolf]

To clarify, if I don't specify xtickinterval in the first case, then I get the following axis -

[Ben C]

Are you including the XTICKUNITS keyword? Set that to "Days". Otherwise IDL will try to choose what it thinks is the most appropriate time unit for your specified interval, which may or may not be correct.

;IDL EXAMPLE CODE: 

x =  TIMEGEN(100, UNITS = 'Days', START = JULDAY(1, 1, 2021, 0, 0, 1))

y = sin(x)

date_label = label_date(date_format=['%N-%D-%Y'])

p = plot(x,y,xtickinterval=20,xtickformat='LABEL_DATE',xtickunits='Days')

[steppenwolf]

I had been setting XTICKUNITS='TIME'. Changing to 'DAYS' definitely seems to make XTICKINTERVAL work as desired :)

Another solution seems to be to set up an automated definition of tick values to pass to the XTICKVALUES keyword.

[Ben C]

I think "Time" is the generic value and ends up with the same behavior as not setting XTICKUNITS at all. Your desired XTICKINTERVAL and XTICKUNITS should always match up, whether it's Year/Months/Day/Hours, otherwise you could get mixed results depending on your XRANGE. 

You can set up the manual tick marks with XTICKVALUES, but IDL should be able to handle all that for you :)

Good luck!