Set NaN values:
a = !values.F_NaN
b = !values.D_NaN
Calls an external UNIX command:
SPAWN, 'command'
Execute one or more IDL statements contained in a string and returns true (1) if sucessful:
example: ret = EXECUTE('plot, indgen(100)')
Plot postscript files. The following makes a color eps file with postscript hardware fonts (useful for changing text in Latex later)
ps_open, outfile, /color, /encapsulated, /ps_fonts
ps_close (when done plotting)
Saving plot window into a PNG image file:
Use keyword true=1 to save in color
write_png, img_file, tvrd(true = 1)
Declaring functions
When functions have not been compiled, calling them with keywords will result in a syntax error. Use FORWARD_FUNCTION to declare those variables are functions:
FORWARD_FUNCTION, name1, name2, ....
Compile routines
To force IDL to compile user-written procedures even if they are already defined (use the keyword /compile_full_file to compile the whole file, not just the function given):
RESOLVE_ROUTINE, name, /compile_full_file
Find the same elements in two idl arrays.
match, a, b, suba, subb
suba contains the indices in vector 'a' with a match in 'b'.
Tab string in IDL: string(9B)
Test for the existence of a file or directory:
test = FILE_TEST(filename) (returns 0 if file does not exist)
Return an array of files in a directory:
files = file_search('/home/blah/*.fits')
Return an array of files recursively through all subdirectories:
files = file_search('/home/blah/',*.fits')
Opening files to write into:
OPENW, unit, filename
PRINTF, unit, stuff
CLOSE, unit
Open files for reading:
OPENR, unit, filename, /get_lun (/get_lun option will assign the unit)
while not(EOF(unit)) do begin
READF, unit, var (type of 'var' must be defined first)
endwhile
CLOSE, unit
Many of these procedures require the IDL Astronomy Library available from GSFC.
Get a FITS header value:
val = SXPAR(header, 'value')
Add/modify FITS header files:
SXADDPAR, header, name, value
Find the pixel value corresponding to an ra and dec in a FITS file:
ADXY, header, ra_d, dec_d, x, y
(ra_d and dec_d should be in decimal degrees)
Returns the string for the sun symbol that is used often in astronomy:
sunsymbol()
To output help file on a topic into postscript:
help topic device=ps > topic.ps