| IDL FAQ [message #5830] |
Tue, 20 February 1996 00:00 |
sterner
Messages: 106
Registered: February 1991
|
Senior Member |
|
|
The IDL FAQ is posted on or about the 20th of each month.
Only the plain text version of the FAQ is posted to the news group.
Version 3.11 of the IDL FAQ is included below.
Changes in version 3.11:
. Fixed the missing end of question T02.
. Added a new question on why memory is not released when an array is
deleted (T27).
The HTML version of the IDL FAQ is available at:
ftp://fermi.jhuapl.edu/www/s1r/idl/idl_faq/idl_faq.html
Ray Sterner sterner@tesla.jhuapl.edu
The Johns Hopkins University North latitude 39.16 degrees.
Applied Physics Laboratory West longitude 76.90 degrees.
Laurel, MD 20723-6099
WWW Home page: ftp://fermi.jhuapl.edu/www/s1r/people/res/res.html
============================================================ ==============
IDL (Interactive Data Language) FAQ
Frequently Asked Questions about the
Interactive Data Language (IDL).
Archive-name: idl-faq
Last-modified: 1996 Jan 18
Version: 3.11
Latest IDL FAQ: See Appendix A02.
FAQ maintainer: Ray Sterner
Email: sterner@tesla.jhuapl.edu
Changes in version 3.11:
. Fixed the missing end of question T02.
. Added a new question on why memory is not released when an array is
deleted (T27).
Previous changes may be found in Appendix A04.
Introduction
This is a list of Frequently Asked Questions about the Interactive Data
Language or IDL. These questions pop up fairly regularly in the newsgroup
comp.lang.idl-pvwave. This list is an attempt to cut down on net traffic
regarding commonly asked questions. Users are encouraged to read through
this list before posting a query to the newsgroup.
As of 1994 Oct 27 Ray Sterner has been maintaining the IDL FAQ. Mike
Schienle was handling this previously, and Patrick Ryan before him; much of
the material and many of the comments here were compiled by them.
A Note from the editor about PV~WAVE:
I do not have any direct experience with PV~WAVE. As such, I will
try to minimize comments which appear to favor one package or the
other. I will, however, welcome concise descriptions of technical and
functional differences between the two packages.
Contents
This list is roughly divided into two categories: general questions and
technical questions. General question numbers are prefixed with a G and
technical ones with a T
General questions
G01. What is IDL?
G02. Where can I contact them?
G03. How do I get IDL?
G04. What is the current version of IDL?
G05. On what systems does IDL run?
G06. What is PV~WAVE and how is it related to IDL?
G07. Are there anonymous FTP sites for IDL?
G08. How can I get help?
G09. Why are there two newsgroups for IDL?
G10. Does anyone at RSI read this group? Is anyone there listening?
G11. When is the next version of IDL due out?
G12. Are there training courses available for IDL?
G13. Is there a World Wide Web server for IDL or IDL based
projects?
G14. How can I find if a routine to do what I want already exists?
Technical questions
T01. Why doesn't polycontour fill open contours?
T02. How do I increase the number of commands stored in the history
buffer?
T03. How do I get IDL to call routines in language X, running
T04. Why does XPALETTE edit my color table incorrectly?
T05. Is there on-line help for IDL?
T06. I run IDL under X in SunOS 4.x, and after I logout, the screen
T07. Sometimes my variables seem to disappear. Why is this?
T08. Are there any editors that support IDL programming?
T09. How do I get 3-D widgets under OpenLook 3.0?
T10. Why does one of the widgets appear red under OpenWindows?
T11. Where are all the IDL routines and userlib procedures?
T12. Does anybody know how to put multiple image plots on one
page in PostScript?
T13. Does case matter in IDL?
T14. How do I set up IDL to get precise control over plot window and
text positioning with either portrait or landscape page orientation on a
PostScript or HP-GL printer?
T15. I get the error message "Code Area Full". What do I do?
T16. Sometimes I get the following error message: % Unable to
allocate memory: to make array. not enough core
T17. How can I set the cursor to a crosshair on my display?
T18. How can I vectorize an equation of two different arrays?
T19. How can I get IDL to work with MacX?
T20. How can I determine if a variable is defined?
T21. Why should KEYWORD_SET not be used to check if a variable
is defined?
T22. What is the undocumented routine TVRDC?
T23.How can IDL be used to generate dynamic GIFs for display on
the World Wide Web?
T24.How can IDL be used to save an IDL window in a specified
graphics format file (GIF, TIFF, ...)?
T25.Why don't my desktop PC applications recognize the preview
portion of IDL EPSI files?
T26.How can I fix widgets that broke with IDL version 4.x.x?
T27.Why is memory not released back to the operating system after
an array is deleted?
Appendix
A01. Disclaimer
A02. Obtaining the latest IDL FAQ
A03. Acknowledgements
A04. Previous version history
GENERAL QUESTIONS:
G01. What is IDL?
IDL is the Interactive Data Language. It is a product of Research Systems,
Inc. (RSI).
The following is quoted from the README file at
rsinc.com:/pub/idl/README. As such, it describes IDL's capabilities in an
understandably subjective manner. ;-)
IDL, Interactive Data analysis Language, is a complete package for the
interactive reduction, analysis, and visualization of scientific data and
images. Optimized for the workstation environment, IDL integrates a
responsive array oriented language with numerous data analysis
methods and an extensive variety of two and three dimensional
displays into a powerful tool for researchers.
IDL supports an extensive data import capability, publication quality
hard copy output, and user-defined Motif graphical user interfaces.
Users can create complex visualizations in hours instead of weeks with
the aid of IDL's high level capabilities and interactive environment.
IDL is useful in physics, astronomy, image and signal processing,
mapping, medical imaging, statistics, and other technical disciplines
requiring visualization of large amounts of data.
Here is a short history of RSI:
[attributed to ali@rsinc.com (Ali Bahrami)]
IDL is a product of Research Systems, Inc., founded in 1977 by David
Stern. The origins of IDL were developed at the Laboratory for
Atmospheric and Space Physics (LASP) at the University of Colorado.
David was one of the people involved in efforts to make computers
easier to use for the physicists at the Lab. The first program in the
evolutionary chain to IDL was named Rufus (named after Dave's dog).
Rufus was a very simple vector oriented calculator that ran on the
PDP-12. It accepted 2 letter codes that specified (1) An arithmetic
operation (2) The input registers to serve as operands, and (3) the
destination register. The next version was the Mars Mariner Spectrum
Editor (MMED) which was a version of Rufus that ran on the PDP-8.
The next program in this line was named SOL, and it also ran on the
PDP-8. Unlike its predecessors, SOL was a real computer language
with a real syntax (no more 2 letter codes). It was an APL influenced
array oriented language with some primitive graphics capabilities. The
resemblance to IDL was there, but very faintly.
In 1977, Dave left LASP to start Research Systems Inc. (RSI) with the
intention of building on the ideas contained in SOL. The initial result
of this endeavor was PDP-11 IDL, which was much more capable than
SOL. Graphics was usually done on Tektronix terminals and outboard
raster graphics displays. I used this version at LASP in 1981 on a
PDP11/34 under RSX-11M in 1981 (I worked as a student at LASP
from 1981 to 1987). I didn't use it for very long though, because 1981
was the year that Dave released the VAX/VMS version of IDL. This
version, which was written in VAX-11 MACRO and FORTRAN,
took advantage of the VAX virtual memory and 32-bit address space,
and was a huge step beyond the PDP-11 version. It used essentially the
same sort of graphics hardware as the PDP-11.
In 1987, Dave decided that Unix workstations were the direction in
which IDL should progress, but porting the current VAX IDL to Unix
didn't make much sense because of its MACRO and FORTRAN
implementation. I had just finished my Masters degree and was looking
for work. Dave hired me and together we wrote the current version of
IDL for Unix on the Sun 3 taking advantage of the re-write to extend
and improve the language. Since then, we've ported it to many Unix
machines and moved it back to VMS. RSI has many other employees
now, but our focus is still the continued development of IDL. Recently,
IDL was ported to PC class systems running Microsoft Windows.
G02. Where can I contact them?
Their address is:
Research Systems, Inc.
2995 Wilderness Place
Boulder, CO 80301
(303) 786-9900 (Voice)
(303) 786-9909 (Fax)
Email:
info@rsinc.com or support@rsinc.com # Internet
ORION::IDL # SPAN
Research Systems' Inc., International Distributor Offices
Austria, Germany, Lichtenstein, Luxembourg, Switzerland
CreaSo, GmbH
Talhof Str. 30 Fax: 49 8105 25623
D82205 Gilching
Telephone: 49 8105 25055 Fax: 49 8105 25623
Contact: Bernhard Kortmann, Germany email: 100137.2421@compuserve.com
Japan
Adam Net Ltd.
Yushimadai Bldg. 2-31-27
Yushima, Bunkyo-ku
Tokyo, 113, Japan
Telephone: 81 35802 2251 Fax: 81 35802 2249
Contact: Taro Ishiguro, email: taro@adamnet.co.jp
United Kingdom
Floating Point Systems UK Ltd.
Ash Court
23 Rose Street
Wokingham
Berks RG11 1XS
United Kingdom
Telephone: 44 734 776333 Fax: 44 734 776433
Contact: Ken Murphy, email: ken@floating.demon.co.uk
France
Fast Parallel Solutions France
1 Place Gustave Eiffel
Silic 267
94578 Rungis Cedex, France
Telephone: 33 1 46 87 25 22 Fax: 33 1 46 87 71 38
Contact: Louis Tauziet, email: 100347.1577@compuserve.com
Italy
Alliant Computer Systems SRL
Centro Direzionale Colleoni
Palazzo Taurus
Ingresso 3
20041 Agrate Brianza MI, Italy
Telephone: 39 39 6091766 Fax: 39 39 6091779
Contact: Chris Stuart & Alberto Meroni, email: cs@alliant.cise.it
Brazil
SulSoft
Rua Sao Luis, 1050
94060-630 Gravatai - RS
Brazil
Telephone: 55 51 488 22 57 Fax: 55 51 470 41 13
Contact: Michael Steinmayer, email: mis@inf.ufrgs.br
Korea
Intersys
373-1 KuSung-Dong
YuSung-Gu
Tae Jun 305-701
Korea
Telephone: 82 42 869 4746 Fax: 82 42 862 9239
Contact: Jong-Sik Yoon, email: jsyoon@isl.kaist.ac.kr
G03. How do I get IDL?
RSI's distribution scheme is unique in that all of the binaries and IDL code
needed are available via anonymous ftp. IDL binaries and code are available
at these sites:
gateway.rsinc.com (192.5.156.17)
pub/idl
boulder.colorado.edu (128.138.240.1)
pub/idl
ftp.Germany.EU.net (192.76.144.75)
shop/CreaSo/IDL
The README file describes which files are needed, how to unpack them,
and how to install them.
If you install IDL without a valid license, you will get IDL's 7 minute demo
mode. This mode is designed for users who are considering buying the
package.
To actually get IDL running for good, you must pay for a license from RSI
and follow their instructions. You will be asked to fill out a form with
information unique to your machine. RSI will create a license key which the
license manager program (lmgrd) reads to validate your license.
As of release 3.1, upgrades to IDL are no longer free. For details about
upgrades and support contracts, contact RSI.
G04. What is the current version of IDL?
IDL 4.0.1 is the current version. It was released August 1995.
G05. On what systems does IDL run?
The information below is from the file RELEASE_LEVEL located at
rsinc.com:/pub/idl/RELEASE_LEVEL. This information applies to release
3.6.1. It is also in the distribution set in $IDL_DIR/notes/currel.doc.
This release supports the following systems:
- Data General Aviion: DG/UX 5.4.1.
- DEC ALPHA: OSF1 2.0.
- DOS based personal computers running Microsoft Windows 3.1.
- Windows NT (Intel x86).
- HP 9000 Series 700: HP-UX 9.01.
- IBM 6000: AIX 3.2.5
- Apple Mac and Power Mac (native) computers running System 7
- Risc Ultrix: Ultrix 4.2.
- SGI: IRIX 5.2
- Sun 4 (sparc): SunOS 4.1.3.
- Sun 4 (sparc): Solaris 2.3 (SunOS 5.3).
- VMS:
[ALPHA] OpenVMS AXP 1.5.
[VAX] VMS 5.1 and up. Standard X windows graphics are
supported at all VMS versions. IDLwidgets are supported
at VMS 5.4-3 at up *if* the host system has version 1.1
of the DECWINDOWS-MOTIF package installed.
The following hardware/operating system combinations are no longer
supported. The last release of these versions have been archived, and no
future development for them will be done:
- Sun 386i (last release: 2.0.4).
- HP 9000 series 300 and 400 (last release: 3.1.0)
- VAX Ultrix (last release: 2.2.2)
- Sun 3 (last release: 3.1.0)
- MIPS running Risc/OS 4.52B (last release: 3.1.0)
G06. What is PV~WAVE and how is it related to IDL?
Around the time that the Unix version of IDL first became available (1988),
Precision Visuals Inc. (PVI) entered into an agreement with RSI under which
they enhanced and resold IDL under the name PV~WAVE. In September of
1990, they exercised an option in that agreement that resulted in the
following:
- They received a copy of the IDL source code as it existed in September
1990 in return for a one-time payment to RSI.
- The connection between RSI and PVI was severed.
IDL and PV~WAVE are now on separate development tracks. Each company
enhances, supports, and maintains its own product.
PVI has since merged with IMSL and is now Visual Numerics, Inc. (VNI).
G07. Are there anonymous FTP sites for IDL?
The sites below contain public domain IDL code.
JHU/APL/S1R IDL library
fermi.jhuapl.edu [128.244.147.18]
/pub/idl
NASA IDL Astronomy User's Library
(VAX) uit.gsfc.nasa.gov [128.183.57.27]
Username: idluser
Password: (Contact landsman@stars.gsfc.nasa.gov for password)
(Unix) idlastro.gsfc.nasa.gov [128.183.57.82]
/
IUE RDAF library
iuesn1.gsfc.nasa.gov [128.183.57.16]
cetus.colorado.edu [128.138.238.151]
/pub
ICUR Spectral Analysis Software
ftp.astro.psu.edu [128.118.147.28]
/pub/nefftp/icur
IDL ROSAT software
legacy.gsfc.nasa.gov [128.183.8.233]
rosat/software/idl
IDLmeteo library
ftp.sma.ch (141.249.3.33)
/pub/idlmeteo
ESRG library
eos.crseo.ucsb.edu [128.111.228.1]
/pub/idl
G08. How can I get help?
RSI has excellent telephone and email support. You can contact them at:
Voice: (303) 786-9900
Fax: (303) 786-9909
Email:
(Internet)
info@rsinc.com # general questions
support@rsinc.com # technical support
(SPAN)
ORION::IDL
Keep in mind, however, that RSI's technical support is for their paying
customers, i.e. those with current support contracts.
G09. Why are there two newsgroups for IDL?
Unfortunately, there are two very different packages with the abbreviation
"IDL". The newsgroup comp.lang.idl is for the Interface Definition
Language. The newsgroup for discussing issues related to RSI's IDL and
VNI's PV~WAVE and IMSL/IDL is comp.lang.idl-pvwave.
G10. Does anyone at RSI read this group? Is anyone there listening?
[ This question was included at the request of RSI. The answer was provided
by Ali Bahrami. -pat ]
Yes, many of us do. We're naturally curious what people think of our
product. We make notes about what people like and dislike and this
influences our decisions.
However, you usually won't get a direct response from us from a
posting to this group. There are many reasons for this. Here are a
couple of the more important ones:
[] We believe that this group should belong solely to the user
community, and should be free of vendor bias and marketing. It should
be noted that both RSI and Visual Numerics (formerly PVI) have
shown great restraint in this matter, and that this group is largely left
to the actual users. (Long term readers will recall some notable
exceptions to this, but in general it is true.)
It could be argued that as long as the topic stays technical, vendor
postings are OK. The problem with this is that one persons technical
posting is another's blatant product plug, and the line between them is
not always obvious.
[] We provide support for our customers via the phone and email. If
you would like an answer from us, you should call us directly. We have
no objection to you sharing the information you get in this manner
with the newsgroup as long as you quote us accurately and separate fact
from conjecture.
In other words, you should view this newsgroup as a way to share
questions and information with other users, not as a way to contact the
vendor.
G11. When is the next version of IDL due out?
IDL 4.0 was released in June 1995.
IDL 4.01 was released in late August 1995 and includes over 140
corrections and enhancements to IDL 4.0.
G12. Are there training courses available for IDL?
[ This question included at the request of RSI. ]
RSI offers a number of IDL training courses for beginning,
intermediate, and advanced IDL users. IDL courses are scheduled
monthly at RSI's training facility in Boulder. On-site IDL courses are
also available. Contact RSI at 303-786-9900 and ask for "training" or
send e-mail to training@rsinc.com for complete scheduling and price
information.
G13. Is there a World Wide Web server for IDL or IDL based projects?
RSI has WWW pages on IDL in general:
http://www.rsinc.com/
Pete Riley's IDL Home Page at the Lunar and Planetary Lab:
http://xlr8.lpl.arizona.edu/idl.html
Wayne Landsman's IDL Astronomy Library World Wide Web home
page:
http://idlastro.gsfc.nasa.gov/homepage.html
The JHU/APL/S1R IDL library WWW page:
http://fermi.jhuapl.edu/s1r/idl/idl.html
Gary Kushner's IDL data acquisition web page:
http://casa.Colorado.EDU:80/casa/personnel/staff/kushner/idl -iii.html
R. Sterner's Color Shaded Releif Maps made by IDL:
http://fermi.jhuapl.edu/states/states.html
E. Loren Buhle, Jr. Ph.D. made a page on AVS IN MEDICAL
TREATMENT PLANNING which also discusses IDL:
http://archive.xrt.upenn.edu/0h/buhle/manuscripts/avs94_pape r.html
G14. How can I find if a routine to do what I want already exists?
One of the most useful tools to find an available routine is Pete Riley's
Searchable List of all IDL Routines.
This list is available from Pete's IDL page at
http://xlr8.lpl.arizona.edu/idl.html.
If you would like to add your IDL library to Pete's list contact him at
uk2@lpl.arizona.edu.
TECHNICAL QUESTIONS:
Note for Sun users:
There is a mini FAQ for Sun IDL in $IDL_DIR/notes, and the following
questions are answered in the file sun.doc:
1. IDL complains about missing fonts when creating widgets.
2. IDL complains about missing bitmap files when creating widgets.
3. How to make IDL work with OpenWindows version 3.0.
4. 3-D appearance for OpenLook IDLwidgets.
5. Why does one of the widgets appear red?
6. Why does pressing the left button while pointing at a pulldown menu
button cause the menu to pop up with the pushpin in? Older versions
of IDL didn't to that.
7. The font used by the list widget is much larger than it used to be, and
I don't like the result on my program.
8. Why do I get "Cannot allocate colormap entry" errors, and why do
they kill IDL?
9. I've changed my .Xdefaults file, but nothing different happened.
Why?
T01. Why doesn't polycontour fill open contours??
This problem is described in the POLYCONTOUR manual page.
RESTRICTIONS:
This routine will NOT draw open contours. To eliminate open
contours in your dataset, surround the original array with a 1-element
border on all sides. The border should be set to a value less than or
equal to the minimum data array value.
For example, if A is an (N,M) array enter:
B = REPLICATE(MIN(A), N+2, M+2) ;Make background
B(1,1) = A ;Insert original data
CONTOUR, B, PATH=Filename ... ;Create the contour file.
[ This problem was fixed in IDL 3.1. ]
The following is from Ray Sterner at Johns Hopkins University:
Here is a very simple algorithm that might be a useful addition to the section
of the FAQ on filled contours. It is for evenly spaced contours only.
Z is an array to be contoured,
CI is the desired contour interval,
C0 is the desired starting color index,
D is the desired step between colors.
T = fix(Z/CI)
M = T - smooth(T,3)
F = (C0 + T*D)*(1-M)
is an array with filled contours with the contours
plotted with color 0. For contours of a different color
simply add M*CC where CC is the desired contour color index.
T02. How do I increase the number of commands stored in the history
buffer?
The system variable !EDIT_INPUT controls command recall. By default, it
is set to 1, causing the last 20 commands to be saved. If it is 0, no commands
are saved. To save more than 20 commands, just put !EDIT_INPUT=50 (or
other large number) in your startup file.
It is important to realize that IDL looks at the value of !EDIT_INPUT the
first time it reads anything from the keyboard, and the size of the history
buffer is fixed after that. Hence, the command must be in a startup file
because entering it at the keyboard is too late.
T03. How do I get IDL to call routines in language X, running under
system Y?
Jeff Valenti has written a sizable document about calling external
FORTRAN routines from IDL. You can find it at
eos.crseo.ucsb.edu:/pub/idl/idl-fortran.Z.
T04. Why does XPALETTE edit my color table incorrectly?
Here is the answer from RSI support:
The color applications such as xpalette and xloadct use a common
block called "colors" to keep track of the color vectors. When you call
tvlct, your vectors are loaded into the colormap, but they are not put
into the colors common block.
When xpalette starts, it checks to see if the colors have been defined in
the common block and uses them if they have. Otherwise it sets them
to the standard black and white colormap, in which r,g,b are each linear
ramps. (The colors are as you expect because there is only one
colormap.)
Admittedly, this is not the most desirable situation. You would like
your colors which you loaded with TVLCT to be recognized by
xpalette. We modified xpalette (and xloadct) to use the current
colormap when they start up by getting the current vectors with
TVLCT.
Another alternative would be to use the following lines to define the
common block prior to calling your current version of xpalette.
[ assume here that you have a routine called "restore" which reads
colors from a file somewhere and creates vectors r, g, and b. -pat ]
IDL> restore, file='ryan.sav', r, g, b ;get the vectors from somewhere
IDL> tvlct, r, g, b
IDL> common colors,r_orig,g_orig,b_orig,r_curr,g_curr,b_curr
IDL> r_orig = r & r_curr = r
IDL> g_orig = g & g_curr = g
IDL> b_orig = b & b_curr = b
IDL> xpalette
T05. Is there on-line help for IDL?
Try ?.
T06. I run IDL under X in SunOS 4.x, and after I logout, the screen
becomes completely blank. Typing in login names and passwords blindly
logs you in again with the correct colors. How to prevent this?
[Note: This is only a problem under OpenWindows2. -pat ]
Add the following to your .Xdefaults:
Idl*colors: -5
which reserves some colors for the colormap so that IDL does not exhaust all
the available colors. (For a nice summary of Sun IDL interactions with
OpenWindows, see $IDL_DIR/notes/sun.doc)
Another solution is to put a call to clear_colormap in your .login file to be
executed after OpenWindows start up.
T07. Sometimes my variables seem to disappear. Why is this?
Quoting the IDL User's Guide, page 10-8:
IDL users may find that all their variables have seemingly disappeared
after an error occurs inside a procedure or function. The misunderstood
subtlety is that after the error occurs, IDL's context is inside the called
procedure, not in the main level. Typing RETALL or RETURN will
make the lost variables reappear.
RETALL is best suited for use when an error is detected in a procedure
and it is desired to return immediately to the main program level
despite nested procedure calls. RETALL issues RETURN commands
until the main program level is reached.
The HELP command can be used to see the current call stack (i.e.,
which program unit IDL is in and which program unit called it).
T08. Are there any editors that support IDL programming?
Yes. For Emacs:
Chris Chase (chase@jackson.jhuapl.edu) has written idl.el, a major mode for
editing IDL code. He has also written idl-shell.el for running IDL as an
inferior process under emacs. URLs for these files are:
ftp://eos.crseo.ucsb.edu/pub/idl/
ftp://fermi.jhuapl.edu/pub/idl_emacs/
Get the files: idl.el and idl-shell.el
Lubos Pochman (lubosp@pvi.com) of VNI has developed a PV~WAVE
major mode. Given the (remaining) strong similarity between PV~WAVE
and IDL, it has many of the features that one would like in such a mode.
URLs for this file are:
ftp://ftp.pvi.com/PVI/emacs/
ftp://eos.crseo.ucsb.edu/pub/idl/
Get the file wave-mode.shar
From John E. Davis, davis@space.mit.edu:
Also available is JED, an extensible programmer's editor that is available for
Unix, VMS, OS/2, MSDOS, and MS Windows. The size of the executable is
only slightly larger than vi. The extension language resembles C. It provides
emacs, EDT, wordstar, and brief editor emulations (Many claim that JED's
EDT emulation is the best around). It is the only freely available editor that
can perform color syntax highlighting on ordinary character-cell color
terminals (e.g., MS-Kermit, etc.) as well as under XWindows (Xjed).
Currently supported programming modes include: C, FORTRAN, (La)TeX
and BiBTeX, DCL, IDL, NROFF, SH, HTML, and SLANG. Other
extensions include mail, rmail, compile, as well as the ability to read GNU
info files. It is available from
ftp://space.mit.edu/pub/davis/jed/
See Appendix A02 for details on using URLs.
T09. How do I get 3-D widgets under OpenLook 3.0?
This subject is discussed on page 53 of the OpenWindows Version 3 User's
Guide Release Manual.
OpenWindows 3.0 added 3-D appearance for widgets. In order for the 3-D
look to work, it must be enabled and the background color must be a medium
tone color such as "grey" or "wheat". Add the following resources to your
~/.Xdefaults file:
For plain IDL:
Idl*threeD: TRUE
Idl*background: PeachPuff2
For IMSL/IDL:
Imslidl*threeD: TRUE
Imslidl*background: PeachPuff2
T10. Why does one of the widgets appear red under OpenWindows?
This subject is discussed on page 53 of the OpenWindows Version 3 User's
Guide Release Manual.
The OLIT widget toolkit, which is used by IDL, added the concept of
"mouseless focus" under version 3.0. The red widget indicates where the
current mouseless focus is. Use the arrow keys to traverse the widgets, and
the spacebar to make a selection.
T11. Where are all the IDL routines and userlib procedures?
The basic routines are not accessible, for obvious reasons. The userlib, statlib
and widget procedures are in $IDL_DIR/lib/. The procedure XDL also
displays the full pathname. The system variable !path also contains the
directory names for all accessible IDL procedures.
T12. Does anybody know how to put multiple image plots on one page in
PostScript?
Because PostScript has scalable pixels, you must specify the xsize and ysize
parameters, as well as the position parameter, in TV or TVSCL. I don't know
about PV-Wave, but the following works in IDL:
; Display four images in a 2x2 grid
; Assume data(x,y,4) = array containing the 4 images
set_plot, 'ps' ;request PostScript output
device, ... ;modify page size, orientation, etc. as desired
ximsize = 0.5*!d.x_size ;define output image size
yimsize = 0.5*!d.y_size ;note: 0.5 assumes 2x2 grid
for i=0,3 do begin ;display the 4 images, using i as position index
tv, data(*,*,i), i, xsize=ximsize, ysize=yimsize
endfor
T13. Does case matter in IDL?
No.
Compiled routines are case insensitive. The only catch is that, on Unix
systems, when executing a script via the .RUN command, the file name
argument must exactly match the file name as it appears on the disk. Once
the routines in the script are compiled, their names can be written in any
case. This is not a problem in operating systems such as VMS that do not
distinguish case for file names. This is usually not a problem under Unix
either since, by convention, most people use lower case file names.
T14. How do I set up IDL to get precise control over plot window and
text positioning with either portrait or landscape page orientation on a
PostScript or HP-GL printer?
(This answer only applies to PostScript and HP-GL printers -- other
printers may differ in having the X and Y offsets measured from the upper
left corner of the portrait page instead of the lower left corner.)
IDL uses portrait page orientation as a default. (The x axis is along the
shorter dimension of the paper.) In portrait orientation the lower left corner
of the page is the origin for the XOFFSET and YOFFSET page offsetting
keywords of the DEVICE command that determine the origin (lower left
corner) of the output window. (Normally one uses XOFFSET=0 and
YOFFSET=0 for portrait orientation.) Size of the output window is
determined by the XSIZE and YSIZE keywords of the DEVICE command.
The origin for graph positioning variables !P.POSITION and !P.REGION is
the output window origin. X and Y coordinates for portrait page orientation
are shown on the sketch below as upper case X and Y.
----------
| | ORIGINAL PORTRAIT PAGE (Printer only prints on
Y | | OUTPUT WINDOW this area.)
| |
| X |
o-----------
| y + | OUTPUT WINDOW ROTATED ABOUT LOWER LEFT CORNER
x | + |
| + |
------------
++++++++++ OUTPUT WINDOW RESIZED FOR LANDSCAPE ORIENTATION
^
| DIRECTION OF NEEDED OFFSET
If device,/landscape is specified, then the output window is rotated 90 deg.
clockwise about the lower left corner of the page. In this condition nothing
will be plotted on the page, since the rotation has carried the output window
entirely off the paper as shown in the sketch above. To correct this mismatch,
the rotated output window must be offset. XOFFSET AND YOFFSET are
still measured in the X and Y coordinates of the portrait page, but now
represent the position of the lower left corner of the rotated (and resized)
output window (marked by an o above) with respect to the lower left corner
of the portrait (actual) page. Hence, one generally uses XOFFSET=0 and
YOFFSET=long_dimension_of_page for landscape orientation.
In landscape orientation, the coordinates for graph positioning variables
!P.POSITION and !P.REGION are the lower case x and y coordinates shown
in the sketch above and having origin marked by the letter o. Position of
output window origin o on the page is, of course, affected by the setting of
XOFFSET and YOFFSET, as explained before. The XSIZE and YSIZE
(output window size) keywords of the DEVICE command are also measured
in the x and y directions when in landscape orientation. The resizing of the
landscape page generally means interchanging the values of XSIZE and
YSIZE appropriate for the portrait page.
Example of settings for a portrait page:
XPAGE=8.5 & YPAGE=11. & XOFFS=0. & YOFFS=0. ;Inches
DEVICE,/INCHES,XSIZE=XPAGE,YSIZE=YPAGE,XOFFSET=XOFFS,YOFFSET =YOFFS
Example of settings for a landscape page:
XPAGE=11. & YPAGE=8.5 & XOFFS=0. & YOFFS=XPAGE ;Inches
DEVICE,/LANDSCAPE,/INCHES,XSIZE=XPAGE,YSIZE=YPAGE,XOFFSET=XO FFS, $
YOFFSET=YOFFS
Example of setting position and size of a plot window:
X0=1.374 & Y0=1.283 & XLEN=3.622 & YLEN=6.157 ;Inches
!P.POSITION=[X0/XPAGE,Y0/YPAGE,(X0+XLEN)/XPAGE,(Y0+YLEN)/YPA GE]
Example of setting position and orientation of a text string:
x0=.35 & y0=.37 ;Inches
xyouts,x0/xpage,y0/ypage,!stime,orient=90,/normal ;Date, time
T15. I get the error message "Code Area Full". What do I do?
IDL sets aside a certain amount of memory area for compiling programs. The
current code and area sizes can be seen with the HELP command, e.g.
IDL> help
% At $MAIN$ .
Code area used: 0% (0/16384), Symbol area used: 0% (2/4096)
These sizes can be increased with the .SIZE command. Quoting the IDL
User's Manual, page 2-11:
These sizes represent a compromise between an unlimited program
space and conservation of memory. User procedures and functions are
compiled in this large program area. After successful compilation, a
new memory are of the required size is allocated to contain the newly
compiled program unit.
Resizing the code and data areas erases the currently compiled main
program and all mail program variables. For example, to extend the
code and data areas to 30000 and 5000 bytes respectively:
.SIZE 30000 5000
Getting "Code Area Full" is often an indication that the routine is large, and
would benefit by decomposition into sub-procedures/functions. It's better to
avoid use of .SIZE because your code will always work on other systems
where the users don't use a large .SIZE setting.
T16. Sometimes I get the following error message:
% Unable to allocate memory: to make array.
not enough core
RSI support replies:
The circumstances described happen when memory becomes
fragmented. Unfortunately, there is nothing you can do except use less
memory in your application, or get more for the system to work with.
T17. How can I set the cursor to a crosshair on my display?
Ray Sterner of Johns Hopkins University has written a procedure for
managing this called crossi. It is in the usr.tar file of the JHU/APL IDL
library mentioned in question G07.
Joel Parker has written a procedure called rdplot which manages this using
an XOR graphics function and provides additional functionality. It is located
in the NASA IDL Astronomy User's Library mentioned in question G07.
T18. How can I vectorize an equation of two different arrays?
From the user community:
I have two different arrays, (8) of float and (300,8) of float. I want to
vectorize the equation and therefore I need to use both arrays in the
same equation. For example :
newarray=cos(small_array)*sin(large_array)
where I want the data in small_array to be used over and over 300
times in this calculation.
From Dan Carr (dan@rsinc.com):
IDL> arr1 = Findgen(8)
IDL> arr2 = Findgen(300, 8)
IDL> newarr = (Replicate(1.0, 300) # Cos(arr1)) * Sin(arr2)
From Dave Landers (landers@tsunami.dseg.ti.com)
to convert an array1(M) to array2(n,M) :
array2 = array1( Lindgen(n,M) / n )
or array2 = replicate(1,n) # array1
to convert an array1(M) to array2(M,n) :
array2 = array1( Lindgen(M,n) MOD M )
or array2 = array1 # replicate(1,n)
T19. How can I get IDL and MacX to work without crashing?
Using MacX v1.2 and IDL cause the Mac to crash quite often. This happens
especially during allocation of color resources or display windows. You can
get around the problem by downgrading to MacX v1.1.7 (apparently Apple
will supply this if you can prove to them that you rightfully own v1.2).
Another solution is to purchase White Pine's eXodus software. Rumors are
that eXodus is an overall better product than MacX. White Pine can be
contacted at:
White Pine Software
40 Simon St. Suite 201 Nashua, NH 03060-3043
phone: 603-886-9050 Fax: 603-886-9051
T20. How can I determine if a variable is defined?
It is often useful to determine if an IDL variable is defined. The is easily
done using the n_elements function which returns 0 if the given variable
is undefined. This is especially useful for setting defaults for keyword
parameters. Here are several examples:
if n_elements(start) eq 0 then start=0
if n_elements(dir) eq 0 then cd, current=dir
T21. Why should KEYWORD_SET not be used to check if a variable is
defined?
From Bill Thompson:
The IDL function KEYWORD_SET() is only designed to be used with
logical variables, i.e. those which can be either True (usually signalled with
the value 1) or False (0). It has the property that if a variable is undefined,
then it returns False, so people often make the mistake of using it to test
whether a variable is defined or not.
To test whether a variable is defined or not, use N_ELEMENTS() instead.
This will return 0 if a variable is undefined, or some positive number
otherwise. Only use KEYWORD_SET for truly Boolean (True/False)
variables.
T22. What is the undocumented routine TVRDC?
From a comp.lang.idl-pvwave post by William Thompson:
The reason that TVRDC is undocumented is because it's not needed any
more. It doesn't do anything that CURSOR doesn't do. TVRDC is only
retained for compatibility with older programs.
In the old days, before X-windows, CURSOR was used to read coordinates
off of line graphics terminals, and TVRDC was used to read coordinates off
of image display devices. With the advent of IDL 2.0, the distinctions
between different kinds of graphics devices were mostly removed, and both
of these functions were merged into CURSOR.
T23. How can IDL be used to generate dynamic GIFs for display on the
World Wide Web?
By Jason Mathews, NASA/ Goddard Space Flight Center:
Common Gateway Interface (CGI) Perl scripts are invoked via submiting a
HTML form , which execute IDL in batch mode, runs a IDL routine to make
a plot of the selected parameters, and writes the results to a GIF. The perl
program output is displayed on the WWW browser as a HTML document
with an inline GIF image.
The IDL program must use the 'Z' device and write the output results to a
GIF file as in the example below:
SET_PLOT, 'Z' ; Select the Z buffer output device
PLOT, x, y, ... ; Draw the plot
image = TVRD() ; Copy the device contents into an image
WRITE_GIF, 'filename.gif', image ; Write image to a GIF file
EXIT ; Exit IDL routine
Examples of various perl programs that use IDL on the web and the
corresponding HTML forms are available via the following URL:
http://coney.gsfc.nasa.gov/Mathews/misc/idl-www.html
Some example WWW-based Data Browsing and Retrieval Systems using
IDL:
NSSDC OMNIWeb: http://nssdc.gsfc.nasa.gov/omniweb/ow.html
NSSDC COHOWeb: http://nssdc.gsfc.nasa.gov/cohoweb/cw.html
WWW/IDL Interface Demo:
http://www.gsfc.nasa.gov/idl/idl_web.html
T24. How can IDL be used to save an IDL window in a specified graphics
format file (GIF, TIFF, ...)?
By Mark Rivers, CARS, Univ. of Chicago (slightly edited)
IDL> plot,x,y,title='This is my plot' ; Make a plot (or display an image).
IDL> image = tvrd() ; Read image into an array.
IDL> tvlct, r, g, b, /get ; Read color table.
IDL> write_gif, file, image, r, g, b ; Save in a GIF image file.
This sequence should work on any windowing display (X, Windows, Mac).
For better speed and more flexibility, first issue the command
SET_PLOT, 'Z'
to write to the Z-buffer pseudo-device. You can set its resolution, and its
write and readback performance is very fast.
[Additional notes by editor] The screen image may be saved in other graphics
formats by using the correct write routine. Some of the routines of interest
are:
write_gif, tiff_write, write_jpeg, write_bmp, ...
Note the different name pattern for tiff_write, check the manuals for
the calling syntax for each routine.
There are also corresponding routines to read the images back into IDL.
Which format is best? GIF images are compressed so take less space than
uncompressed images. JPEG images are also compressed but with a lossy
compression, that is, the image when read back into IDL is not identical to
the image written. However JPEG images can look very good and also often
can be more highly compressed than GIF. Some images may be larger (much
larger) using JPEG as compared to GIF, try both and compare. GIF images
are widely used on the World Wide Web, JPEG is also supported by some
web browsers. TIFF may be needed for publishing purposes.
T25. Why don't my desktop PC applications recognize the preview
portion of IDL EPSI files?
By Troy Klein, Johns Hopkins Applied Physics Lab
Quoting the IDL version 4.0 online help for the PREVIEW keyword, "Set
this keyword to add a 'device independent screen preview' to the PostScript
output file, in encapsulated PostScript interchange format (EPSI). Use this
keyword only with encapsulated output. Many, but certainly not all, desktop
publishing and word processing programs will display this screen preview
when the file is imported into a document."
The EPSI format is not compatible with some of the more popular Windows
and Macintosh applications. Windows applications expect the preview image
to be in TIFF format and Macintosh applications expect the preview image to
be in PICT format and in the resource fork of the EPS file. I have found the
EPSI file to be compatable with Framemaker for UNIX/X windows.
There are two workarounds available for Mac users and two for Windows
users, all are similar. If you are using IDL on a UNIX machine, there is a
package available (as of 8/2/95) on the popular University of Michigan Mac
shareware/freeware archive (use the mirror site at ftp://mirrors.aol.com)
titled "ps2epsmac", which uses Ghostscript and NetPBM on a UNIX
machine to interpret the postscript and create a new EPS file in Macbinary
format with the PICT preview. There are several Mac programs available (
StuffitExpander, Fetch, etc.) to interpret the Macbinary file. I have had
great success in using this method to import IDL EPS files into Word,
Powerpoint, and MacDraw Pro. There is a similar package at the archive
titled "ps2epsplus" which does the same thing, but all on a Mac.
For UNIX IDL users trying to import IDL EPS files into Windows
applications, there is a package called "ps2epsf" which can be located using
an Archie search. This package essentially does the same thing as the
UNIX/Mac package but produces an EPS file with a TIFF preview. The
second solution for Windows users is the Windows applicationi GSview
(which can also be found with archie). Version 1.2 claims to be capable of
adding preview images to EPS files.
T26. How can I fix widgets that broke with IDL version 4.x.x?
In IDL version 4, the sizing and layout of IDL's Motif widgets changed in
several ways. This can cause problems. Widget changes are discussed in a file
available from RSI at
ftp://boulder.colorado.edu/pub/rsi/idl/notes/widgets.txt.
T27. Why is memory not released back to the operating system after an
array is deleted?
By Eric Korpela of Berkeley
This is a result of IDL being written in C and using the C library functions
(malloc and free) for memory allocation. In most C libraries, memory that is
freed is NOT returned to the operating system. The C program retains this
memory and will reuse it for future calls to malloc (assuming that the new
allocation will fit in the freed block).
Another way of considering it is in terms of how memory allocation is done
under UNIX. New memory is allocated using brk() or sbrk() which control
the size of the data segment. These routines are called by malloc().
Suppose you allocate 3 1 MB regions of memory under C.
char *p1=(char *)malloc(3*1024*1024);
char *p2=(char *)malloc(3*1024*1024);
char *p3=(char *)malloc(3*1024*1024);
Here's what your data segment would look like assuming malloc had to call
sbrk().
------------------------------------------------------------ ---
prev stuff | overhead | 3MB | overhead | 3MB | overhead | 3MB |
------------------------------------------------------------ ---
^ ^ ^ ^
p1 p2 p3 end of segment.
Now we free(p1).
------------------------------------------------------------ ----
prev stuff | overhead | free | overhead | 3MB | overhead | 3MB |
------------------------------------------------------------ ----
^ ^ ^
p2 p3 end of segment
Notice that the free memory is still in the data segment. If free had called brk
to reduce the size of the segment, the 3MB pointed to my p3 would be
outside the data segment! SIGSEGV city! If free had moved the allocated
memory to lower addresses so the segment size could be reduced without
losing data, then p2 and p3 would point to invalid addresses, and we'd be
forced to use handles rather than pointers and call GetPointerFromHandle()
every time we wanted to access the memory. Ick! Just like Windows!
APPENDIX
A01. Disclaimer:
I do not work for RSI and I am in no way answerable to them. Questions and
answers in this document are culled from the user community. No warranty,
express or implied exists regarding this document. Permission to copy all or
part of this work is granted, provided that the copies are not made or
distributed for resale.
A02. Obtaining the latest IDL FAQ
The current IDL FAQ may be accessed at fermi.jhuapl.edu [128.244.147.18]
in directory www/s1r/idl/idl_faq
HTML version: idl_faq.html (compressed: idl_faq.html.Z)
Plain Text: idl_faq.txt (compressed: idl_faq.txt.Z)
The URL (Uniform Resource Locator) for this file is:
ftp://fermi.jhuapl.edu/www/s1r/idl/idl_faq/idl_faq.html
How to interpret the URL
Using a WWW (World Wide Web) Browser, for example mosaic:
mosaic ftp://fermi.jhuapl.edu/www/s1r/idl/idl_faq/idl_faq.html
Save the file using the Save as ... option.
Using anonymous ftp:
ftp fermi.jhuapl.edu
Login: anonymous
Password: enter your email address
cd www/s1r/idl/idl_faq
get file
bye
Additions and Corrections
Send additions and corrections to:
Ray Sterner
sterner@tesla.jhuapl.edu
A03. Many thanks to the following for their contributions
black@breeze.rsre.mod.uk (John Black)
claflin@claes.space.lockheed.com (Scott Claflin)
edelsohn@npac.syr.edu (David Edelsohn)
fireman@iuegtc.DNET.NASA.GOV (Gwyn Fireman)
gurman@umbra.gsfc.nasa.gov (Joseph B. Gurman)
jdlb@kukui.IFA.Hawaii.Edu (JF Pitot de La Beaujardiere)
kashyap@oddjob.uchicago.edu (Vinay Kashyap)
mayor@vaxine.larc.nasa.gov (Shane Mayor)
oet@maz.sma.ch (Thomas Oettli)
rmmoss@Texaco.COM (Robert M. Moss)
sterne@dublin.llnl.gov (Philip Sterne)
William.T.Thompson.1@gsfc.nasa.gov (William Thompson)
valenti@soleil.Berkeley.EDU (Jeff Valenti)
sterner@tesla.jhuapl.edu (Ray Sterner)
joel@stars.gsfc.nasa.gov (Joel Parker)
landers@tsunami.dseg.ti.com (David Landers)
dan@rsinc.com (Dan Carr)
denisef@rsinc.com (Denise Fields)
mathews@nssdc.gsfc.nasa.gov (Jason Mathews)
rivers@cars3.uchicago.edu (Mark Rivers)
klein@hobbes.jhuapl.edu (Troy Klein)
davis@space.mit.edu (John Davis)
korpela@ssl.berkeley.edu (Eric Korpela)
Previous IDL FAQ maintainers:
Patrick Ryan: founded the IDL FAQ
Mike Schienle: from 12/01/93 to 10/27/94
A04. IDL FAQ Versions History
Changes in version 3.11:
. Fixed the missing end of question T02.
. Added a new question on why memory is not released when an array is
deleted (T27).
Changes in version 3.10:
. Updated RSI's home page in G13.
. Made a few minor changes in the URLs that point to fermi (the home site
of the IDL FAQ).
. Fixed the broken link to Gary Kushner's IDL data acquisition web page in G13.
Changes in version 3.9:
. New question on how to find IDL routines (G14).
. New question on widgets breaking with IDL version 4 (T26).
. Minor change to G04.
Changes in version 3.8:
. New question on Encapsulated Postscript Previews (T25).
. Generalized question T08 to non-emacs editors
that support IDL programming (first is JED from MIT).
. Minor addition to G11 When is the next
version of IDL due out?
Changes since version 3.7:
. New question on screen save to a graphics format image (T24).
Changes since version 3.6:
. New question on using IDL to make WWW images (T23).
. IDL 4.0 release dates added (G04, G11).
Changes since version 3.5:
. Added question T22: What is the undocumented routine TVRDC?
. Added question T21: Why should KEYWORD_SET not be used to check if
a variable is defined?
Changes since version 3.4:
. Added Pete Riley's IDL Home Page at LPL (G13).
. Added RSI's International Distributor Offices (G02).
Changes since version 3.3:
. Added Gary Kushner's IDL data acquisition WWW page (G13).
. Dropped Hal Mueller's U.S. map page (was out of service) (G13).
. Added R. Sterner's Color Shaded Relief Maps WWW page (G13).
. Added a new question on detecting undefined variables (T20).
. Added a hyperlink to the directory in question T03.
Changes since version 3.2:
. Updated IDL release dates.
. Added Wayne Landsman's IDL Astronomy Library WWW page.
. Added JHU/APL/S1R IDL Library WWW page.
Changes since version 3.1:
. Made it easier to find where to get the latest FAQ.
. Retroactively changed last version to 3.0, the first HTML version.
Changes since version 3.0:
. New FAQ maintainer.
. First HTML version.
. Added an Appendix for some previous material.
Changes since version 2.8:
. Added Power Macintosh to systems which IDL runs on.
. Updated "Training" contact information.
Changes since version 2.7:
. Updated information regarding next release dates.
. Changed reference to openwin3.doc to sun.doc.
Changes since version 2.6:
. New question T19 added regarding MacX and IDL.
. Updated information regarding current IDL versions.
. Reference to current IDL version changed from 3.5.1 to 3.6.1.
Changes since version 2.5:
. T18 responses corrected.
Changes since version 2.4:
. New question T18 added regarding vectorizing an equation.
. Address change for FAQ maintainer.
. Address change for FAQ location.
Changes since version 2.3:
. New question T17 added regarding cross-hair cursor.
. Additional info for NASA ftp site.
. Additional information provided for question T01 regarding contours.
. Question G09 referred to the "other" IDL as Interface Description
Language, rather than the correct Interface Definition Language.
Changes since version 2.2:
. Question G13 regarding IDL World Wide Web info added.
. JHU/APL IDL library name changed from nansen to fermi. Nansen will
still work for some time.
. Release dates for upcoming versions of IDL revised.
Changes since version 2.1:
. Due to resource problems, the lumpi.informatik.uni-dortmund.de site
is no longer carrying IDL binaries. However, the distribution is now
available from ftp.Germany.EU.net (192.76.144.75).
. Reference to current IDL version changed from 3.5 to 3.5.1.
. Mention of compressed version of FAQ included.
. Added ESRG to list of FTP sites.
The End
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