en Copyright 1997-2013, David W. Fanning david@idlcoyote.com (David Fanning) Mon, 20 May 2013 15:40:51 GMT david@idlcoyote.com (David Fanning) http://www.idlcoyote.com/index.html IDL Programming Tips and Examples http://www.idlcoyote.com/images/coyote_tips.jpg http://www.idlcoyote.com/index.html http://www.idlcoyote.com/code_tips/fastdist.php An interesting discussion on the IDL newsgroup suggests that doing distance calculations with complex numbers may be the fastest way to perform these calculations. This article explores this possibility with example code. article 1020 at idlcoyote.com Mon, 20 May 2013 15:40:51 GMT http://www.idlcoyote.com/code_tips/multiplots.php There are many ways to create multiple plots in IDL. This article looks at a few of them and gives suggestions for deciding which method is best for the job. article 1019 at idlcoyote.com Thu, 16 May 2013 21:08:49 GMT http://www.idlcoyote.com/code_tips/extractcircle.php It is easy to extract rectangular regions from an image, but what if you want to extract a circular region? This article explains one of the more intuitive ways to create a circular image mask to extract image data. article 1018 at idlcoyote.com Mon, 13 May 2013 14:40:52 GMT http://www.idlcoyote.com/code_tips/sphericalgrid.php Quite frequently you find yourself with randomly positioned data values that are associated with a latitude and longitude value. You often want to display this kind of data as a contour plot on a map projection. Traditionally, the Triangulate/Trigrid method is used to grid random data values into a 2D grid that can be contoured. And, there is provision in this method for gridding to the "surface of a sphere," which seems like a good thing to do for latitude/longitude data. You would be gravely mistaken. This article explains why and illustrates a couple of methods, using GridData, that will do this correctly. article 1017 at idlcoyote.com Sun, 14 Apr 2013 16:44:16 GMT http://www.idlcoyote.com/code_tips/addpoisson.php Adding random Poisson noise to an image is a little harder than just adding random uniform noise to an image, since you have to compute the Poisson random deviate for each value in the image. This article describes how to do it and includes a function that will do it for you. article 1016 at idlcoyote.com Sun, 14 Apr 2013 16:44:16 GMT http://www.idlcoyote.com/cg_tips/windrose.php I've add a new program to the Coyote Library, cgWindRose, that can create wind rose diagrams from wind speed and direction arrays. These diagrams are used in meteorological applications to measure the frequency, speed, and direction of winds over a defined period of time. article 1015 at idlcoyote.com Wed, 06 Mar 2013 16:53:48 GMT http://www.idlcoyote.com/gallery/index.html#AVI_MOVIE I've added an IDL program and data to the Coyote Plot Gallery that demonstrates how to create an AVI movie of a year's worth of monthly precipitation data in IDL that can be played in any AVI player (e.g, Windows Media Player). IDL 8.1 or higher is required to run the program. article 1014 at idlcoyote.com Sun, 24 Feb 2013 17:45:09 GMT http://www.idlcoyote.com/gallery/index.html#GE_IMAGE I've added the ability to create KMZ files to the Coyote Library routines that support creating KML files for display in Google Earth. You can find an example of this in an IDL program to display precipitation data with a color bar in the Coyote Plot Gallery. An updated version of the Coyote Library will be required to run the example program. article 1013 at idlcoyote.com Sun, 24 Feb 2013 17:45:09 GMT http://www.idlcoyote.com/cg_tips/cglandscape.php Some users think Coyote Graphics routines can only produce PostScript output in Landscape mode. This article explains this apparent bias in Coyote Graphics routines and describes several simple methods to coax Coyote Graphics routines into producing any kind of PostScript output you like. article 1012 at idlcoyote.com Wed, 20 Feb 2013 15:59:19 GMT http://www.idlcoyote.com/gallery/gallery.html I've spent most of the weekend adding new plot types to the Coyote Plot Gallery. In putting together some of the image plots, I noticed I had introduced a problem into cgImage when I was last playing with image transparency. Please update your Coyote Library distribution, and cgImage in particular, if you want to run the code in the Gallery. article 1011 at idlcoyote.com Mon, 28 Jan 2013 01:56:00 GMT http://www.idlcoyote.com/cg_tips/multicmds.php This article describes several different methods for collecting multiple Coyote Graphics commands together and outputting them to a raster file, such as a JPEG or PNG file. article 1010 at idlcoyote.com Fri, 25 Jan 2013 20:36:58 GMT http://www.idlcoyote.com/gallery/gallery.html The Coyote IDL Graphics Plot Gallery is now open. The purpose of the gallery is to collect in one place example code and data to produce a wide variety of graphics plots. This is the place where you can learn best practices and techniques to get the most out of your own graphics programs. An updated Coyote Library is required to run the example programs found in the gallery. article 1009 at idlcoyote.com Thu, 24 Jan 2013 06:33:00 GMT http://www.idlcoyote.com/cg_tips/twowindows.php Creating multiple resizeable Coyote Graphics windows is done exactly the same way multiple windows are created in normal graphics output, but instead of using the Window command, you use the cgWindow command. To select the "current" graphics window, use cgSet instead of WSet. This is meant to mimic normal graphics useage, but has proven confusing to a number of Coyote Graphics users. article 1008 at idlcoyote.com Mon, 14 Jan 2013 03:09:24 GMT http://www.idlcoyote.com/cg_tips/transimage.php You are not the only one who has been confused about how to work with transparent and overplotted images with cgImage. I've been confused, too. But, this weekend I decided to sort it out for myself and write it down so I don't forget it. This article is the result. It explains how cgImage goes about creating a transparent image, and illustrates with examples how to use the various cgImage keywords that pertain to transparent images. It will be useful reading for me as well as you! article 1007 at idlcoyote.com Sun, 13 Jan 2013 19:33:58 GMT http://www.idlcoyote.com/programs/cgimage.pro I've been confused about how transparent and overplotted images work in cgImage. I decided to spend the weekend figuring it out. In the end, this required some changes to cgImage and a new article that will remind me how this works, so I don't forget it again! article 1006 at idlcoyote.com Sun, 13 Jan 2013 19:33:58 GMT http://www.idlcoyote.com/cg_tips/taylordiagram.php I've added a new program, cgTaylorDiagram, to the Coyote Library today to create Taylor Diagrams of user data. Taylor Diagrams are a way to show three statistical properties of the data on a 2D plot: RMS difference, correlation, and standard deviation. article 1005 at idlcoyote.com Thu, 10 Jan 2013 19:38:27 GMT http://www.idlcoyote.com/idldoc/cg/cgtaylordiagram.html I have added a new program to the Coyote Library today to draw Taylor Diagrams of user data. Taylor Diagrams are used to show three statistical measures on a 2D plot: RMS difference, correlation, and standard deviation. article 1004 at idlcoyote.com Thu, 10 Jan 2013 19:38:27 GMT http://www.idlcoyote.com/cg_tips/polarwind.php Mark Piper showed a nice visualization of polar wind vector plots on his blog recently. This article demonstrates how to create the same visualization using Coyote Graphics for those people who do not yet have IDL 8. article 1003 at idlcoyote.com Mon, 07 Jan 2013 14:03:05 GMT http://www.idlcoyote.com/programs/zip_files/coyoteprograms.zip Several map programs have been updated this week, including cgMap, cgMap_Grid, and cgMapVector. This would be a good time to update your Coyote Library. article 1002 at idlcoyote.com Mon, 07 Jan 2013 14:03:05 GMT http://www.idlcoyote.com/idldoc/cg/cgimage2kml.html I have added a FlyTo keyword to this program that allows you to set the location and elevation of the user's "eye" over an image that you are adding to Google Earth. In practice, this allows you to "fly to" the image when it is opened in Google Earth. article 1001 at idlcoyote.com Mon, 31 Dec 2012 22:08:33 GMT http://www.idlcoyote.com/idldoc/cg/cgkml_lookat__define.html This new program implements a KML "LookAt" object in a KML file. A LookAt object allows you to "fly to" a particular location and elevation on the Earth. I use the object in the FlyTo keyword in cgImage2KML to allow the user to center the eye above an image location in Google Earth. article 1000 at idlcoyote.com Mon, 31 Dec 2012 22:08:33 GMT http://www.idlcoyote.com/cg_tips/extracolors.php Occasionally unwanted colors show up in Coyote Graphics color bars or other graphics output. People have been confused about where these colors come from and how to eliminate them. This article explains what is happening and shows you how to eliminated unwanted colors from your output. article 999 at idlcoyote.com Thu, 20 Dec 2012 14:15:51 GMT http://www.idlcoyote.com/idldoc/cg/cglayout.html This is a program that makes it easy to obtain the plot positions used by !P.Multi when setting up a plot grid. This is useful, for example, when you would like to display a color bar with every filled contour plot or image displayed in a multi-plot grid of plots. article 998 at idlcoyote.com Thu, 20 Dec 2012 14:15:51 GMT http://www.idlcoyote.com/cg_tips/convert.php Many people don't know where to get started when they want to convert their old, reliable IDL program to use Coyote Graphics functionality. It seems like a daunting prospect, but it is simpler than you think. Here are three tips you can learn in five minutes to help you do the job! article 997 at idlcoyote.com Mon, 17 Dec 2012 16:32:00 GMT http://www.idlcoyote.com/cg_tips/colorupdate.php I started pulling on a small thread to improve the speed of Coyote Graphics routines in some circumstances, and before I knew it 18 programs in the Coyote Library had been changed! Be sure to get a new update of the Coyote Library with these important changes that increase the speed of Coyote Graphics routines, dramatically in some cases, through modified color handling procedures. article 996 at idlcoyote.com Mon, 17 Dec 2012 16:32:00 GMT http://www.idlcoyote.com/ng_tips/boxaxes.php Getting a box axes on a map using the Map function in IDL 8.2.1 is not as simple as setting the Box_Axes keyword. This article describes the bugs and limitations to the Map function you have to work around to get what you want. article 995 at idlcoyote.com Sun, 02 Dec 2012 18:48:15 GMT http://www.idlcoyote.com/cg_tips/textoidl.php Users who are more familar with TeXtoIDL than they are with cgSymbol can now embed TeXtoIDL control sequences directly into Coyote Graphics title and axis text to create Greek characters and other symbols. TeXtoIDL must be installed and on the IDL path to use this functionality. article 994 at idlcoyote.com Sun, 25 Nov 2012 01:11:39 GMT http://www.idlcoyote.com/code_tips/otsu_threshold.php The Otsu Threshold can be used to find the statistically optimal threshold to separate a bimodal population of pixels into two separate populations. The Otsu Method chooses the threshold by maximizing the inter-class variances of the two populations. article 993 at idlcoyote.com Sun, 25 Nov 2012 01:11:39 GMT http://www.idlcoyote.com/idldoc/cg/cgdotplot.html Yikes! I changed the name of cgDot_Plot to cgDotPlot to be more consistent with other Coyote Library routines, then forgot to change all my descriptions of the program. Sorry! article 992 at idlcoyote.com Mon, 19 Nov 2012 14:59:06 GMT http://epod.usra.edu/blog/2012/11/aurora-australis-and-magellanic-clouds.html Here is a rare view of the Aurora Australis by IDL programmer and occasional astronomer Andrew Cool. article 991 at idlcoyote.com Mon, 19 Nov 2012 00:08:52 GMT http://www.idlcoyote.com/idldoc/cg/cgimage.html The cgImage program has been updated to allow transparent images to be displayed in IDL 6.4 and earlier. Previously this was not allowed because the 24-bit Z-graphics buffer was not available in these versions of IDL. The updated version of cgImage uses pixmaps instead of the Z-graphics buffer for these early versions of IDL. article 990 at idlcoyote.com Sun, 18 Nov 2012 17:27:29 GMT http://www.idlcoyote.com/idldoc/cg/cgdot_plot.html A new Coyote Graphics program, cgDot_Plot, has been introduced into the Coyote Library. This program was commissioned and donated to the IDL user community by Marta Yebra of CSIRO/Australia. Dot plots are useful for comparing values for separate experiments or conditions. article 989 at idlcoyote.com Sun, 18 Nov 2012 17:27:29 GMT http://www.idlcoyote.com/idldoc/cg/cgotsu_threshold.html A new Coyote Graphics program, cgOtsu_Threshold, has been introduced into the Coyote Library. This program is used to find the optimal threshold for separating a bimodal distribution of image pixels into two populations. article 988 at idlcoyote.com Sun, 18 Nov 2012 17:27:29 GMT http://www.idlcoyote.com/idldoc/cg/cgdraw_roi.html A new Coyote Graphics program, cgDraw_ROI, has been introduced into the Coyote Library. This program is a Coyote Graphics wrapper for the built-in Draw_ROI program. article 987 at idlcoyote.com Sun, 11 Nov 2012 16:21:52 GMT http://www.idlcoyote.com/idldoc/cg/cgcontour.html A C_ANNOTATION keyword has been added to cgContour to allow contour lines to be labelled with user-defined strings. This new keyword supports embedded symbols and characters. article 986 at idlcoyote.com Sat, 10 Nov 2012 16:40:30 GMT http://www.idlcoyote.com/cg_tips/embedsymbols.php The cgCheckForSymbols and the cgSymbol programs have been updated to handle superscripts and subscripts. The symbols \up and \down implement the !U and !D format codes, and reduce the size of the superscript or subscript by 0.62 percent. The symbols \exp and \sub implement !E and !I format codes and reduce the size of the superscript or subscript by 0.44 percent. article 985 at idlcoyote.com Fri, 09 Nov 2012 21:14:58 GMT http://www.idlcoyote.com/idldoc/cg/cgnumber_formatter.html The Number_Formatter program has been retired and is replaced by the cgNumber_Formatter program. This program has been updated to handle NaN and Inf values properly, and it now works MUCH better for numbers between 0.0001 and 1.0. In this case, the number of decimals specified with the DECIMAL keyword is taken to mean the number of significant digits that should be displayed. article 984 at idlcoyote.com Fri, 09 Nov 2012 21:14:58 GMT http://www.idlcoyote.com/ps_tips/maccolors.php The Mac Preview application adds extra, nonexistent colors to PostScript files when it converts them to PDF output for viewing. Such colors don't exist in the PostScript file and will not be seen if you view your PostScript file with another PostScript viewer. This article suggests several you may want to use instead. article 983 at idlcoyote.com Mon, 05 Nov 2012 13:37:14 GMT http://www.idlcoyote.com/programs/zip_files/coyoteprograms.zip If you haven't updated your Coyote Library in awhile, you may be shocked to know how many of your files are completely out of date. Nearly 30 programs have been changed or added in the past two months. Take advantange of new features and new functionality by updating your Coyote Library now. Old and retired programs are also available to you in the Coyote/Retired directory. But, bug fixes and new functionality are only added to current programs. article 982 at idlcoyote.com Mon, 05 Nov 2012 02:49:48 GMT http://www.idlcoyote.com/cg_tips/image2kml.php Over the past week I have written about 10 new programs that make it extremely easy to write KML files to display any 2D array or image as a terrain overlay in Google Earth. This article introduces you to the programs and code you need. In addition to adding the images as overlays on the Google Earth terrain, you can also add color bars and other legends as screen overlays. Screen overlays are images that stay in a fixed location on the Google Earth display, which the Google Earth terrain rotates and zooms beneath them. They can be turned on or off, as needed. Images can be be created with transparency, and missing data can be made completely transparent. article 981 at idlcoyote.com Mon, 05 Nov 2012 02:43:12 GMT http://www.idlcoyote.com/idldoc/cg/cgimage.html A new Transparent keyword has been added to cgImage that allows any image to be displayed with any amount of transparency between 0 and 100 percent. In addition, missing values in the image can be made completely transparent. article 980 at idlcoyote.com Mon, 05 Nov 2012 02:28:05 GMT http://www.idlcoyote.com/fileio_tips/transparent.html I have written a new program, cgTransparent, that can make a a transparent image out of any 2D or true-color image. Images can also be created from any IDL graphics window. In addition, missing data can be made completely transparent. This is an implementation of the same algorithm that cgImage uses with its Transparent keyword to make any displayed image transparent. article 979 at idlcoyote.com Mon, 05 Nov 2012 02:28:05 GMT http://www.idlcoyote.com/ng_tips/histoplotoff.php The new Histogram keyword for the new Plot function brings a new histogram-like look to the plot, but, uh, the plot is wrong. This article explains why you may want to continue using cgHistoplot for a little while longer. article 978 at idlcoyote.com Mon, 05 Nov 2012 02:21:53 GMT http://www.idlcoyote.com/map_tips/warptomap.php Often we have data in which each data pixel is associated with a latitude and longitude value. This article explains how a new Coyote Library program, cgWarpToMap, can provide Map_Patch-like functionality to users of Coyote Library map projection routines. article 977 at idlcoyote.com Mon, 05 Nov 2012 02:16:18 GMT