en Copyright 1997-2009, David W. Fanning david@dfanning.com (David Fanning) Fri, 12 Mar 2010 17:11:34 GMT david@dfanning.com (David Fanning) http://www.dfanning.com/index.html IDL Programming Tips and Examples http://www.dfanning.com/images/coyote_tips.jpg http://www.dfanning.com/index.html http://www.dfanning.com/programs/catalyst/source/utilities/modified_map_grid.pro Map grid labels are not correctly clipped to the map plot boundaries when using either hardware or true-type fonts with Map_Grid. This program is a slightly modified version of Map_Grid that incorporates an algorithm that checks the label point to be sure it is inside the map plot boundary before it is drawn. Using this program it is now possible to produce IDL maps in PostScript hardware fonts. article 466 at dfanning.com Fri, 12 Mar 2010 17:11:34 GMT http://www.dfanning.com/programs/catalyst/source/utilities/fixed_map_grid.pro This program is designed to fix another problem with Map_Grid, in which occasionally grid lines are not drawn properly. I've further modified the program to use the same new clipping algorith used in the Modified_Map_Grid program described above. article 465 at dfanning.com Fri, 12 Mar 2010 17:11:34 GMT http://www.dfanning.com/programs/catalyst/source/graphics/map_grid__define.pro I have modified this program to use the new Modified_Map_Grid program described above, so it properly clips map grid labels with hardware and true-type fonts. I have also tweaked the AUTODRAWGRID method to better draw grids automatically. article 464 at dfanning.com Fri, 12 Mar 2010 17:11:34 GMT http://www.dfanning.com/programs/catalyst/source/applications/imgwin.pro I have updated this program so that if a GeoTiff file is opened, and the user has chosen to add a map grid to the image, that the AUTODRAWGRID keyword is set on the Map_Grid object. This allows me to open a variety of GeoTiff files and still have nice looking map grids put on top of the image. article 463 at dfanning.com Thu, 11 Mar 2010 16:59:40 GMT http://www.dfanning.com/programs/catalyst/source/graphics/map_grid__define.pro I have added an AUTODRAWGRID keyword to this program. If set, this allows the grid object to automatically calculate appropriate latitude and longitude values to draw, based on the ranges in the supporting map object. In general, this provides nice grids in a variety of situations. I use it, for example, when working with GeoTiff files. article 462 at dfanning.com Thu, 11 Mar 2010 16:59:40 GMT http://www.dfanning.com/programs/catalyst/source/coordinates/mapcoord__define.pro A small typo in the spelling of the SEMIMINOR_AXIS keyword in the GetProperty has been corrected. Also, program documentation has been updated and improved. article 461 at dfanning.com Thu, 11 Mar 2010 14:40:56 GMT http://www.dfanning.com/programs/catalyst/source/applications/gpd_viewer.pro Small changes have been made in the way well-known NSIDC GPD file formats are loaded, and I had accidentally reversed the semi-major and semi-minor axes when I saved the GPD file to disk. article 460 at dfanning.com Thu, 11 Mar 2010 14:40:56 GMT http://www.dfanning.com/programs/dataviewer.zip Changes have been made to the Catalyst DataViewer application that allow it to read near real time DMSP SSM/I daily polar gridded brightness temperature images. These include images processed with the NASA Team (NT) algorithm. The National Snow and Ice designations for these new data sets are nsidc-0080 and nsidc-0081. article 459 at dfanning.com Tue, 09 Mar 2010 14:23:12 GMT http://www.dfanning.com/code_tips/addfield.html This article describes how Struct_Assign can be used to copy the contents of one array of structures to another array of structures containing a new structure field. This makes adding a new field to an array of structures less onerous than it would be otherwise. article 458 at dfanning.com Sun, 07 Mar 2010 16:25:30 GMT http://www.dfanning.com/map_tips/warpimage.html Here is an example of how you can use Map_Proj_Image to warp an image in one map projection into another map projection. This is useful, for example, if you wish to compare two images that are gridded to different map projection grids. article 457 at dfanning.com Mon, 01 Mar 2010 01:48:59 GMT http://www.dfanning.com/math_tips/oneplus.html Wayne Landsman points out that one plus one sometimes equals one in IDL. Here is what you need to know to avoid this mistake yourself. article 456 at dfanning.com Sun, 28 Feb 2010 18:36:39 GMT http://www.dfanning.com/programs/catalyst/source/applications/gpd_viewer.html A fix to a problem that caused the grid location to change if the map scale keywords were changed. And a fix that caused the map projection to return to its non-zoomed state if the grid location was changed by clicking in the window. article 455 at dfanning.com Sun, 28 Feb 2010 17:01:52 GMT http://www.dfanning.com/programs/fsc_window.pro I've added a REPLACE keyword to the program, which allows the user to replace the IDL command that is displayed in the current graphics window with another. This gives you the opportunity to use the same graphics window over and over again, without creating a separate graphics window for each IDL graphics command you wish to display. article 454 at dfanning.com Fri, 26 Feb 2010 15:30:52 GMT http://www.dfanning.com/powerpoint/map_projections_idl.pdf These are the slides of my "Map Projections in IDL: Navigating Images" presentation to the 24 February 2010 IDL User's Group meeting in Boulder, CO. article 453 at dfanning.com Fri, 26 Feb 2010 14:05:29 GMT http://www.dfanning.com/programs/randomnumbergenerator__define.pro I fixed a problem in the Cleanup method where I was not cleaning up the seed pointer properly. article 452 at dfanning.com Fri, 26 Feb 2010 14:05:29 GMT http://www.dfanning.com/programs/findmapboundary.pro I added XRANGE and YRANGE keywords. The same information is returned as before, but in a more convenient package for me to use further downstream. article 451 at dfanning.com Fri, 26 Feb 2010 14:05:29 GMT http://www.dfanning.com/programs/findmapboundary.pro One of the essential requirements for navigating images is to know the boundary of the image in XY (sometimes called UV) coordinates. These are essential for setting up the map coordinate space for drawing on or interacting with the image. This program will find the XY boundary for those files that encode the information. Currently the program works with GeoTiff files, CF 1.4 complaint netCDF files, and GPD files that were created with the GPD_Viewer in the Catalyst Library. article 450 at dfanning.com Mon, 22 Feb 2010 13:26:48 GMT http://www.dfanning.com/programs/ncdf_isvalidfile.pro This program is just a simple addition the netCDF files I released last week. I just needed as fast, reliable way to tell if a file is a netCDF file or not, and nothing like that is available in the normal IDL distribution. This program tries to open the given file as a netCDF file. If that fails, then I assume the file is not a valid netCDF file and return a 0. If it succeeds, I return a 1. article 449 at dfanning.com Mon, 22 Feb 2010 13:26:48 GMT http://www.dfanning.com/programs/catalyst/source/coordinates/ncdf_coord.pro Last week I introduced some new programs to work with netCDF files. This is a new program that follows on those. It allows map projection and grid information to be read out of a CF 1.4 compliant netCDF file in such a way that a MapCoord object for navigating the netCDF variables can be created automatically. NetCDF files are famous for NOT following conventions, so I am sure there will be files that cannot be parsed correctly, but this program is working for the files I work with on a daily basis. I expect frequent updates over time to make it more robust. The program, unlike the other netCDF programs used last week, utilizes Catalyst Library functionality, and so lives in the Catalyst Library distribution. (The Catalyst Library is becoming so central to my own programming needs, that I expect it will shortly be rolled into the Coyote Library itself.) article 448 at dfanning.com Sun, 21 Feb 2010 15:22:58 GMT http://www.dfanning.com/programs/catalyst/source/utilities/fixed_map_grid.pro A couple of weeks ago I described a "fix" to the built-in IDL routine MAP_GRID which allowed me to correct a problem in my GPD_Viewer application in which grid lines were not always rendered correctly. I incorporated that fix into my MAP_GRID object in the Catalyst Library and thought my problems were solved. Not so. Yesterday I noticed that the "fixed" program was, in some circumstances, causing double grid lines to be drawn in my IMGWIN program when I was automatically navigating GeoTIFF files! Sigh. The sad reality is that to get my programs to work correctly, sometimes I need the "fixed" program and sometimes I don't. So, to give myself this flexibility I have put the "fixed" program in its own file (and added it to the Utilities directory in the Catalyst Library) and added keywords to the programs that use it (GPD_VIEWER, IMGWIN, and the MAP_GRID object) to allow me to select the file depending upon what I am doing with the map grid. It's a lousy solution, but until I know more about exactly what the problem is, I don't know a better way to solve it. article 447 at dfanning.com Sun, 21 Feb 2010 15:22:58 GMT http://www.dfanning.com/programs/catalyst.zip I'm preparing a presentation on map projections for this week's IDL Users Group conference. As usual, that has brought on a a flurry of programming changes as I tend to use programs in new ways, which reveal either bugs or new ideas for how I would like things to work. A number of these changes were in Catalyst Library routines. In the Applications directory, IMGWIN and GPD_VIEWER changed. In the Coordinates directory, the GEOCOORD and MAPCOORD objects changed, and a new file, NCDF_COORD was added (described separately). In the Graphics directory, the MAP_GRID, MAP_OUTLINE, and MAP_PLOTS objects all changed. I have added a new program, FIXED_MAP_GRID, to the Utilities directory. This program is also described separately. article 446 at dfanning.com Sun, 21 Feb 2010 15:22:58 GMT http://www.dfanning.com/programs/ncdf_tools.zip I have a general need to be able to create, browse, and write netCDF files in an extremely flexible way. In particular, I want to be able to copy variables and attributes from one file to another without thinking too much about it. To this end, I borrowed heavily (well, I stole most of the good ideas, really) from Mark Hadfield's Motley Library and its wonderful netCDF routines. When I started this project, I thought Mark's routines could use more documentation and error handling. When I finished, I realized I hadn't added much value to what Mark had already provided. But, of course, hindsight is 20-20. I have learned a lot about netCDF files, and certainly enough to know I am probably going to be surprised in the future about how little I know. In any case, these programs have provided me with some new tools for working with netCDF files and I thought they may be of interest to a wider audience. Because most of these tools are written as objects, and because that scares the bejesus out of many IDL users, I have provided an example file, NCDF_File_Examples, that shows you exactly how to create a netCDF file, copy some of the contents to another netCDF file, and then read the netCDF file to do something useful in IDL. I have been particularly careful to document these routines so they can be used by a wider audience. In addition to Mark, I have been greatly enlightened in my netCDF studies by IDL newsgroup regulars Paul van Delst and Ken Bowman. article 445 at dfanning.com Wed, 17 Feb 2010 15:02:53 GMT http://www.dfanning.com/programs/errorlogger__define.pro The purpose of an error logger, of course, is to create a file with errors in it. This is a Good Thing, except during program development, when all the starting and stopping of programs can cause error logs to accumulate. To deal with the clutter, it is now possible to set a NOCLUTTER keyword on the error logger. This sets both the ALERT and DESTROY_ON_DELETE keywords, and makes it impossible to set the status of the error logger to the error condition. Thus, the error log file is created, the user hears about errors, but the file is always deleted when the error logger object is destroyed, preventing file build-up. Also, a PRINT keyword has been added to the AddText method. This allows the user to add informational text to a file, while simultaniously sending the text to the IDL console. In other words, it provides a method for logging what in the past were PRINT statements. article 444 at dfanning.com Wed, 17 Feb 2010 13:56:58 GMT http://www.dfanning.com/map_tips/nostatedraw.html Under certain conditions Map_Continents fails to draw map boundaries. Here is an example where it fails to draw all the states in the Northeast United States. One alternative is to draw the states using shapefiles, and this article describes how to do this to fix the missing state problem shown here. article 443 at dfanning.com Tue, 16 Feb 2010 03:45:34 GMT http://www.dfanning.com/catalyst/howtoinstall.html Coyote has been on the warpath lately. I don't know if it's the new vegan diet my wife has us on or what, but he is making life totally miserable for me. He is into everything. Today I learned that my catalyst.zip file didn't have the same files in it as my catalyst directory. Sigh... I don't know what to make of it. I'll probably have to go elk hunting this year. Until it settles down, you might want to grab new versions of both the Coyote and Catalyst libaries. I have no idea what he will be up to tomorrow! article 442 at dfanning.com Wed, 10 Feb 2010 23:26:13 GMT http://www.dfanning.com/code_tips/hasdisplay.html Running IDL from a CRON job or from a remote login often fails because IDL can't connect to the X Window system. Either the DISPLAY environmental variable is not set or can't be set. There is no way to programmatically check for this condition. You have to try to make a connection and fail. This article describes a simple IDL function that can do that job for you and alert you before you do something you are going to regret. article 441 at dfanning.com Wed, 10 Feb 2010 23:26:13 GMT http://www.dfanning.com/programs/catalyst/source/applications/imgwin.pro An inconsistency in variable naming ("thisImage" instead of "theImage") showed up today when I was trying to navigate a GeoTIFF image. Fixed now. article 440 at dfanning.com Wed, 10 Feb 2010 16:08:44 GMT http://www.dfanning.com/programs/catalyst/source/coordinates/geocoord.pro My map projection woes continue. An upcoming talk on map projections for the IDL User's Group meeting will either be interesting or totally embarrassing. Today I ran into a GeoTIFF file that had it's GTRasterTypeGeoKey set to 2, which indicates the pixels are point data, rather than area data. I think this may be a mistake in the file, but in any case I have removed my check for this in the GeoCoord program. It doesn't appear to make any difference in this case. I'll keep an eye on this in case something changes. article 439 at dfanning.com Wed, 10 Feb 2010 16:08:44 GMT http://www.dfanning.com/programs/catalyst/source/coordinates/mapcoord__define.pro Not my day today. I found another error in the MapCoord object. This one involves using the SPHERE_RADIUS keyword. Doing this will access a non-existent "datum" field in the object. This has to be changed to "thisDatum". Fixed in all places where this occurs. Thanks to a user for spotting this. article 438 at dfanning.com Tue, 09 Feb 2010 21:40:21 GMT http://www.dfanning.com/programs/catalyst/source/coordinates/mapcoord__define.pro I found an extremely embarrassing error in my MapCoord object this morning. If the map projection you were trying to create was passed in as a string (e.g., 'UTM') then the map projection information was stored incorrectly in the object. If you passed the map projection in as an index (e.g., 101) then it was stored correctly. Sorry I didn't discover this error sooner, but I almost always use indices when I use this object. Fixed in this release. article 437 at dfanning.com Tue, 09 Feb 2010 19:46:16 GMT http://www.dfanning.com/documents/fanning_consulting.html Need help writing an IDL application? Like to consult an IDL expert? Quality IDL programming guaranteed. Currently accepting new IDL programming and consulting opportunities. Pressure of college tuition bills guarantees proprietor will not be offended by small projects, tight deadlines, or chinzy budgets! Call today for quality IDL programming: 970-221-0438. article 046 at dfanning.com Wed, 02 Apr 2008 03:42:50 GMT http://www.dfanning.com/adventures/index.html Want to know more about Coyote? Here are stories and essays of recent adventures. article 008 at dfanning.com Wed, 02 Apr 2008 03:42:50 GMT