1. A brief introduction to IDL
Greg Michael
Planetology and Remote Sensing
Institute of Geosciences
Freie Universitaet Berlin

2. A brief introduction to IDL
Why IDL for planetary data processing?
Array processing language
Powerful visualisation facilities
This short intro intended to give an idea about what IDL is
Some IDL basics
Arrays
File handling
Strings
Worked example: read a VICAR image and save it as a TIFF file
Mars Express HRSC/OMEGA data workshop, St. Louis, May 2008

3. IDL: some basics Arrays Files Strings Easy to create: a=indgen(10)
print,a
Easy to manipulate (other languages typically require a loop to do this, with one iteration for each element):
b=a*10
print,b
Easy to introduce complex array operations. Here, a matrix multiplication:
c=a#a
print,c
Easy to visualise:
d=indgen(400)#indgen(400)
tvscl,d
Files
To record an array in a file:
openw,1,"D:\mydocs\tmp\a.tmp"
writeu,1,a
close,1
And to recover it:
e=intarr(10)
openr,1,"D:\mydocs\tmp\a.tmp"
readu,1,e
To check it’s correct:
print,e
Strings
Variables which store text, e.g.
s="this is a string"
print,s
Can also have string arrays:
t=replicate(s,10)
print,t
print,transpose(t)
And write them to a text file:
openw,1,"D:\mydocs\tmp\t.txt"
printf,1,transpose(t)
Mars Express HRSC/OMEGA data workshop, St. Louis, May 2008

4. IDL example: extract image from VICAR file
Get the file
berlin.de/mex4/0515/h0515_0000.ir4.50
Read the file header:
filename="D:\mydocs\data\HRSC\0515\h0515_0000.ir4. 04"
openr,1,filename
s=“”
readf,1,s
close,1
print,s
The values are stored as a series of expressions separated by spaces
key=strsplit(s,' ',/extract)
print,transpose(key)
print,transpose(key[0:10])
To get an individual value:
val=strsplit(key[0],'=',/extract)
print,val
lblsize=val[1]
Extract the image data
Also need to obtain NL and NS in the same way
im=bytarr(ns,nl)
openr,1,filename
point_lun,1,lblsize
readu,1,im
close,1
tvscl,im
tvscl,congrid(im,300,700)
Save the image as a TIFF file
write_tiff,"D:\mydocs\tmp\im.tif",im
And a small version as a jpeg:
write_jpeg,"D:\mydocs\tmp\im.jpg",congrid(im,300,700)
***
Help
Press F1, or Help-Contents from the menu
Function library
E.g. strsplit, congrid, tvscl, write_tiff
Mars Express HRSC/OMEGA data workshop, St. Louis, May 2008