<s>
IDL	B-Language
,	O
short	O
for	O
Interactive	B-Language
Data	I-Language
Language	I-Language
,	O
is	O
a	B-Language
programming	I-Language
language	I-Language
used	O
for	O
data	B-General_Concept
analysis	I-General_Concept
.	O
</s>
<s>
It	O
is	O
popular	O
in	O
particular	O
areas	O
of	O
science	O
,	O
such	O
as	O
astronomy	O
,	O
atmospheric	O
physics	O
and	O
medical	B-Application
imaging	I-Application
.	O
</s>
<s>
IDL	B-Language
shares	O
a	O
common	O
syntax	O
with	O
PV-Wave	B-Language
and	O
originated	O
from	O
the	O
same	O
codebase	B-General_Concept
,	O
though	O
the	O
languages	O
have	O
subsequently	O
diverged	O
in	O
detail	O
.	O
</s>
<s>
There	O
are	O
also	O
free	B-Application
or	O
costless	B-License
implementations	O
,	O
such	O
as	O
GNU	B-Language
Data	I-Language
Language	I-Language
(	O
GDL	B-Language
)	O
and	O
(	O
FL	O
)	O
.	O
</s>
<s>
IDL	B-Language
is	O
vectorized	B-Application
,	O
numerical	B-General_Concept
,	O
and	O
interactive	O
,	O
and	O
is	O
commonly	O
used	O
for	O
interactive	O
processing	O
of	O
large	O
amounts	O
of	O
data	O
(	O
including	O
image	B-Algorithm
processing	I-Algorithm
)	O
.	O
</s>
<s>
The	O
syntax	O
includes	O
many	O
constructs	O
from	O
Fortran	B-Application
and	O
some	O
from	O
C	B-Language
.	O
</s>
<s>
IDL	B-Language
originated	O
from	O
early	O
VMS	B-Operating_System
Fortran	B-Application
,	O
and	O
its	O
syntax	O
still	O
shows	O
its	O
heritage	O
:	O
</s>
<s>
Note	O
that	O
the	O
operation	O
in	O
the	O
second	O
line	O
applies	O
in	O
a	O
vectorized	B-Application
manner	O
to	O
the	O
whole	O
100-element	O
array	O
created	O
in	O
the	O
first	O
line	O
,	O
analogous	O
to	O
the	O
way	O
general-purpose	O
array	B-Application
programming	I-Application
languages	I-Application
(	O
such	O
as	O
APL	B-Language
,	O
J	B-Language
or	O
K	B-Application
)	O
would	O
do	O
it	O
.	O
</s>
<s>
This	O
example	O
contains	O
a	O
division	O
by	O
zero	O
;	O
IDL	B-Language
will	O
report	O
an	O
arithmetic	B-Algorithm
overflow	I-Algorithm
,	O
and	O
store	O
a	O
NaN	O
value	O
in	O
the	O
corresponding	O
element	O
of	O
the	O
array	O
(	O
the	O
first	O
one	O
)	O
,	O
but	O
the	O
other	O
array	O
elements	O
will	O
be	O
finite	O
.	O
</s>
<s>
The	O
NaN	O
is	O
excluded	O
from	O
the	O
visualization	O
generated	O
by	O
the	O
command	O
.	O
</s>
<s>
As	O
with	O
most	O
other	O
array	B-Application
programming	I-Application
languages	I-Application
,	O
IDL	B-Language
is	O
very	O
fast	O
at	O
doing	O
vector	O
operations	O
(	O
sometimes	O
as	O
fast	O
as	O
a	O
well-coded	O
custom	O
loop	O
in	O
Fortran	B-Application
or	O
C	B-Language
)	O
but	O
quite	O
slow	O
if	O
elements	O
need	O
processing	O
individually	O
.	O
</s>
<s>
Hence	O
part	O
of	O
the	O
art	O
of	O
using	O
IDL	B-Language
(	O
or	O
any	O
other	O
array	B-Application
programming	I-Application
language	I-Application
,	O
for	O
that	O
matter	O
)	O
for	O
numerically	B-General_Concept
heavy	O
computations	O
is	O
to	O
make	O
use	O
of	O
the	O
built-in	O
vector	O
operations	O
.	O
</s>
<s>
The	O
predecessor	O
versions	O
of	O
IDL	B-Language
were	O
developed	O
in	O
the	O
1970s	O
at	O
the	O
Laboratory	O
for	O
Atmospheric	O
and	O
Space	O
Physics	O
(	O
LASP	O
)	O
at	O
the	O
University	O
of	O
Colorado	O
at	O
Boulder	O
.	O
</s>
<s>
The	O
first	O
program	O
in	O
the	O
evolutionary	O
chain	O
to	O
IDL	B-Language
that	O
Stern	O
developed	O
was	O
named	O
Rufus	O
;	O
it	O
was	O
a	O
simple	O
vector-oriented	O
calculator	O
that	O
ran	O
on	O
the	O
PDP-12	B-Device
.	O
</s>
<s>
A	O
version	O
of	O
Rufus	O
developed	O
on	O
the	O
PDP-8	B-Device
was	O
the	O
Mars	O
Mariner	O
Spectrum	O
Editor	O
(	O
MMED	O
)	O
.	O
</s>
<s>
Later	O
,	O
Stern	O
wrote	O
a	O
program	O
named	O
SOL	O
,	O
which	O
also	O
ran	O
on	O
the	O
PDP-8	B-Device
.	O
</s>
<s>
Unlike	O
its	O
predecessors	O
,	O
it	O
was	O
a	O
true	O
programming	O
language	O
with	O
a	O
FORTRAN-like	O
syntax	O
.	O
</s>
<s>
The	O
first	O
RSI	O
product	O
was	O
IDL	B-Language
for	O
the	O
PDP-11	O
.	O
</s>
<s>
In	O
this	O
release	O
,	O
the	O
graphics	O
supported	O
by	O
IDL	B-Language
were	O
primarily	O
Tektronix	O
terminals	O
and	O
raster	O
graphics	O
displays	O
.	O
</s>
<s>
RSI	O
sold	O
its	O
first	O
IDL	B-Language
licenses	O
to	O
NASA	O
's	O
Goddard	O
Space	O
Flight	O
Center	O
and	O
Ball	O
Aerospace	O
&	O
Technologies	O
Corp	O
.	O
in	O
1979	O
.	O
</s>
<s>
Two	O
years	O
later	O
RSI	O
released	O
an	O
initial	O
VAX/VMS	B-Operating_System
version	O
of	O
IDL	B-Language
,	O
which	O
was	O
written	O
in	O
VAX	B-Language
MACRO	I-Language
and	O
FORTRAN	B-Application
.	O
</s>
<s>
The	O
National	O
Center	O
for	O
Atmospheric	O
Research	O
(	O
NCAR	O
)	O
,	O
the	O
University	O
of	O
Michigan	O
,	O
the	O
University	O
of	O
Colorado	O
,	O
and	O
the	O
Naval	O
Research	O
Laboratory	O
started	O
to	O
use	O
IDL	B-Language
with	O
this	O
version	O
.	O
</s>
<s>
In	O
1987	O
RSI	O
shifted	O
development	O
work	O
of	O
IDL	B-Language
to	O
the	O
Unix	B-Application
environment	O
,	O
which	O
required	O
a	O
complete	O
re-write	O
of	O
the	O
code	O
in	O
C	B-Language
rather	O
than	O
a	O
port	O
of	O
the	O
existing	O
version	O
of	O
VAX	O
IDL	B-Language
.	O
</s>
<s>
Stern	O
and	O
Ali	O
Bahrami	O
rewrote	O
IDL	B-Language
for	O
Unix	B-Application
on	O
the	O
Sun	O
3	O
,	O
taking	O
advantage	O
of	O
the	O
re-write	O
to	O
extend	O
and	O
improve	O
the	O
language	O
.	O
</s>
<s>
Subsequently	O
,	O
IDL	B-Language
was	O
further	O
expanded	O
and	O
ported	O
to	O
several	O
variants	O
of	O
Unix	B-Application
,	O
VMS	B-Operating_System
,	O
Linux	O
,	O
Microsoft	O
Windows	O
(	O
1992	O
)	O
,	O
and	O
Mac	O
OS	O
(	O
1994	O
)	O
.	O
</s>
<s>
Widgets	O
were	O
added	O
to	O
IDL	B-Language
in	O
1992	O
,	O
providing	O
event-driven	B-Application
programming	I-Application
with	O
graphical	B-Application
user	I-Application
interfaces	I-Application
.	O
</s>
<s>
In	O
1997	O
ION	O
(	O
IDL	B-Language
On	O
the	O
Net	O
)	O
,	O
a	O
web	O
server-based	O
system	O
,	O
was	O
commercially	O
released	O
.	O
</s>
<s>
The	O
first	O
version	O
of	O
ENVI	B-Application
,	O
an	O
application	O
for	O
remote	B-Application
sensing	I-Application
multispectral	O
and	O
hyperspectral	B-Application
image	I-Application
analysis	O
written	O
in	O
IDL	B-Language
,	O
was	O
released	O
in	O
1994	O
.	O
</s>
<s>
ENVI	B-Application
was	O
created	O
,	O
developed	O
and	O
owned	O
by	O
Better	O
Solutions	O
Consulting	O
,	O
LLC	O
,	O
until	O
it	O
was	O
purchased	O
from	O
BSC	O
in	O
October	O
2000	O
by	O
Eastman	O
Kodak	O
coincident	O
with	O
their	O
purchase	O
of	O
RSI	O
.	O
</s>
<s>
RSI	O
sold	O
,	O
marketed	O
and	O
supported	O
ENVI	B-Application
under	O
the	O
terms	O
of	O
a	O
license	O
agreement	O
with	O
BSC	O
,	O
LLC	O
from	O
1994	O
through	O
October	O
2000	O
.	O
</s>
<s>
New	O
object	O
and	O
pointer	O
types	O
,	O
and	O
limited	O
object-oriented	B-Language
programming	I-Language
capabilities	O
,	O
were	O
added	O
to	O
IDL	B-Language
in	O
1997	O
.	O
</s>
<s>
IDL	B-Language
has	O
been	O
applied	O
widely	O
in	O
space	O
science	O
,	O
for	O
example	O
in	O
solar	B-Application
physics	I-Application
.	O
</s>
<s>
The	O
European	O
Space	O
Agency	O
used	O
IDL	B-Language
to	O
process	O
almost	O
all	O
of	O
the	O
pictures	O
of	O
Halley	B-Application
's	I-Application
Comet	I-Application
taken	O
by	O
the	O
Giotto	O
spacecraft	O
.	O
</s>
<s>
The	O
team	O
repairing	O
the	O
Hubble	O
Space	O
Telescope	O
used	O
IDL	B-Language
to	O
help	O
them	O
diagnose	O
anomalies	O
in	O
the	O
main	O
mirror	O
.	O
</s>
<s>
In	O
1995	O
,	O
astronauts	O
on	O
board	O
a	O
Space	O
Shuttle	O
used	O
IDL	B-Language
loaded	O
on	O
a	O
laptop	O
to	O
study	O
ultraviolet	O
radiation	O
.	O
</s>
<s>
Currently	O
,	O
amongst	O
other	O
applications	O
,	O
IDL	B-Language
is	O
being	O
used	O
for	O
most	O
of	O
the	O
analysis	O
of	O
the	O
SECCHI	O
part	O
of	O
the	O
STEREO	O
mission	O
at	O
NRL	O
,	O
USA	O
,	O
and	O
at	O
the	O
Rutherford	O
Appleton	O
Laboratory	O
,	O
UK	O
.	O
</s>
<s>
,	O
IDL	B-Language
is	O
now	O
owned	O
and	O
maintained	O
by	O
Harris	O
Geospatial	O
Solutions	O
.	O
</s>
<s>
As	O
a	O
computer	O
language	O
,	O
IDL	B-Language
:	O
</s>
<s>
provides	O
COMMON	B-Application
block	I-Application
declarations	O
and	O
system	O
variables	O
to	O
share	O
global	O
values	O
among	O
routines	O
.	O
</s>
<s>
provides	O
a	O
basic	O
form	O
of	O
object-oriented	B-Language
programming	I-Language
,	O
somewhat	O
similar	O
to	O
Smalltalk	B-Application
,	O
along	O
with	O
operator	O
overloading	O
.	O
</s>
<s>
implements	O
a	O
persistent	O
,	O
global	O
heap	O
of	O
pointer	O
and	O
object	O
variables	O
,	O
using	O
reference	B-General_Concept
counting	I-General_Concept
for	O
garbage	O
collection	O
.	O
</s>
<s>
compiles	O
to	O
an	O
interpreted	O
,	O
stack-based	O
intermediate	O
p-code	O
( à	O
la	O
Java	B-Language
virtual	I-Language
machine	I-Language
)	O
.	O
</s>
<s>
provides	O
composite	O
data	O
types	O
such	O
as	O
character	O
strings	O
,	O
homogeneous-type	O
arrays	O
,	O
lists	O
,	O
hash	B-Algorithm
tables	I-Algorithm
,	O
and	O
simple	O
(	O
non-hierarchical	O
)	O
record	O
structures	O
of	O
mixed	O
data	O
types	O
.	O
</s>
<s>
Some	O
of	O
these	O
features	O
,	O
which	O
make	O
IDL	B-Language
very	O
simple	O
to	O
use	O
interactively	O
,	O
also	O
cause	O
difficulties	O
when	O
building	O
large	O
programs	O
.	O
</s>
<s>
IDL	B-Language
programmers	O
can	O
avoid	O
many	O
of	O
these	O
problems	O
by	O
using	O
square	O
brackets	O
for	O
array	O
indexing	O
,	O
thereby	O
avoiding	O
conflicts	O
with	O
function	O
names	O
which	O
use	O
parentheses	O
.	O
</s>
<s>
ITT	O
Visual	O
Information	O
Solutions	O
(	O
ITT	O
VIS	O
)	O
,	O
the	O
developers	O
of	O
IDL	B-Language
,	O
have	O
taken	O
explicit	O
steps	O
to	O
prevent	O
bytecode	O
compatibility	O
with	O
other	O
environments	O
.	O
</s>
<s>
Files	O
containing	O
compiled	O
routines	O
use	O
a	O
binary	O
tagged-data-structure	O
format	O
that	O
has	O
not	O
been	O
officially	O
published	O
but	O
has	O
been	O
investigated	O
and	O
documented	O
by	O
users	O
but	O
also	O
contain	O
the	O
following	O
notice	O
as	O
ASCII	O
text	O
embedded	O
within	O
each	O
saved	O
file	O
:	O
"	O
IDL	B-Language
Save/Restore	O
files	O
embody	O
unpublished	O
proprietary	O
information	O
about	O
the	O
IDL	B-Language
program	O
.	O
</s>
<s>
Reverse	O
engineering	O
of	O
this	O
file	O
is	O
therefore	O
forbidden	O
under	O
the	O
terms	O
of	O
the	O
IDL	B-Language
End	O
User	O
License	O
Agreement	O
(	O
IDL	B-Language
EULA	O
)	O
.	O
</s>
<s>
All	O
IDL	B-Language
users	O
are	O
required	O
to	O
read	O
and	O
agree	O
to	O
the	O
terms	O
of	O
the	O
IDL	B-Language
EULA	O
at	O
the	O
time	O
that	O
they	O
install	O
IDL	B-Language
.	O
</s>
<s>
Software	O
that	O
reads	O
or	O
writes	O
files	O
in	O
the	O
IDL	B-Language
Save/Restore	O
format	O
must	O
have	O
a	O
license	O
from	O
ITT	O
Visual	O
Information	O
Solutions	O
explicitly	O
granting	O
the	O
right	O
to	O
do	O
so	O
.	O
</s>
<s>
Also	O
,	O
that	O
provision	O
of	O
the	O
IDL	B-Language
EULA	O
has	O
no	O
effect	O
in	O
Australia	O
,	O
as	O
a	O
result	O
of	O
sections	O
and	O
of	O
that	O
country	O
's	O
Copyright	O
Act	O
.	O
</s>
<s>
The	O
following	O
graphics	O
were	O
created	O
with	O
IDL	B-Language
(	O
source	O
code	O
included	O
)	O
:	O
</s>
