Add tplot Greek-letter crib sheet

idl/general/examples/crib_tplot_greek_letters.pro

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+;+
+; NAME:
+;     crib_tplot_greek_letters
+;
+; PURPOSE:
+;     Demonstrates how to use IDL text-formatting escape sequences for
+;     Greek letters in tplot component labels (legends) and axis titles.
+;
+; NOTES:
+;     The !X escape returns text to the default font.  Existing SPEDAS
+;     loaders use these same escapes in ytitles, for example !4h!X for
+;     theta, !4u!X for phi, and !4l!X for micro-style labels.
+;
+;     These are IDL direct-graphics text/font escapes used by existing
+;     SPEDAS labels.  Exact glyph appearance can depend on the active
+;     graphics device/font and IDL runtime.
+;
+;     To run from IDL:
+;       .compile crib_tplot_greek_letters
+;       crib_tplot_greek_letters
+;
+;     Type ".c" at each stop to continue through the examples.
+;
+; SEE ALSO:
+;     crib_tplot, crib_tplot_annotation, crib_tplot_panel_labels
+;
+; $LastChangedBy$
+; $LastChangedDate$
+; $LastChangedRevision$
+; $URL$
+;-
+
+pro crib_tplot_greek_letters
+
+  ; Make this crib self-contained.
+  store_data, '*', /delete
+
+  npts = 64L
+  times = time_double('2020-01-01/00:00') + dindgen(npts)*60D
+  phase = findgen(npts)/10.0
+
+  y = fltarr(npts, 3)
+  y[*, 0] = sin(phase)
+  y[*, 1] = cos(phase)
+  y[*, 2] = 0.5*sin(phase + 0.8)
+
+  store_data, 'greek_label_demo', data={x: times, y: y}
+
+  ;---------------------------------------------------------------------
+  ; Greek letters in tplot component labels
+  ;---------------------------------------------------------------------
+  print, 'Example 1: use the labels option to put Greek letters in tplot labels.'
+  print, '           labflag controls where the labels are drawn.'
+
+  options, 'greek_label_demo', labels=['!4h!X component', '!4u!X component', '!4l!X component']
+  options, 'greek_label_demo', colors='bgr', labflag=-1
+  options, 'greek_label_demo', ytitle='Greek labels'
+  options, 'greek_label_demo', ysubtitle='demo'
+
+  tplot, 'greek_label_demo'
+
+  print, 'Type ''.c'' to continue to the title/subtitle example.'
+  stop
+
+  ;---------------------------------------------------------------------
+  ; Greek letters in titles and subtitles
+  ;---------------------------------------------------------------------
+  print, 'Example 2: the same IDL text escapes can be used in tplot titles.'
+  print, '           !4h!X renders theta, !4u!X renders phi, and !4l!X renders micro.'
+
+  options, 'greek_label_demo', ytitle='Angles !4h!X and !4u!X'
+  options, 'greek_label_demo', ysubtitle='!4l!XV example'
+  options, 'greek_label_demo', labflag=-1
+
+  tplot, 'greek_label_demo'
+
+  print, 'Type ''.c'' to continue to the reference table.'
+  stop
+
+  ;---------------------------------------------------------------------
+  ; Compact reference table for common SPEDAS/IDL text escapes
+  ;---------------------------------------------------------------------
+  print, 'Common IDL direct-graphics escapes useful in tplot text:'
+  print, '  These escapes are used by existing SPEDAS labels; exact glyphs can'
+  print, '  depend on the active graphics device/font and IDL runtime.'
+  print, '  !4h!X    theta, as used by existing SPEDAS Wind theta labels'
+  print, '  !4u!X    phi, as used by existing SPEDAS Wind phi labels'
+  print, '  !9Q!X    theta-like symbol font label used by Wind plasma moments'
+  print, '  !9F!X    phi-like symbol font label used by Wind plasma moments'
+  print, '  !4l!X    micro/mu-style escape used by SPEDAS time tick labels'
+  print, '  !U...!N  superscript, for example cm!U-3!N'
+  print, '  !D...!N  subscript'
+  print, '  !C       line break in tplot titles/subtitles'
+
+  print, 'Done with crib_tplot_greek_letters.'
+
+end