INTRODUCTION
Idrisi is a Geographic Information System for the IBM/Microsoft compatible DOS (Disk Operating System) and Microsoft Windows environment developed for research and education by Dr. J. Ronald Eastman, Clark University Graduate School of Geography. It is maintained and distributed internationally on a non-profit basis. At the time of this publication both Idrisi for DOS (4.1) and Idrisi for Windows (2.1) were available and supported by the Idrisi Project at Clark University.
An IBM/Intel 80386 compatible computer is recommended as a minimum for acceptable performance in Idrisi (DOS version), especially when working with large files. A co-processor (80387) or Intel 80486 compatible computer will greatly improve the performance of Idrisi, especially on some of the more compute-intensive operations. Minimum acceptable performance, however, will require at least an IBM-AT or compatible (Intel 80286) with suitable disk space for processing and storage of a user database, which may be any subset or geographic window of the global files provided. As a practical minimum, display requires at least EGA graphics with 16 colors. VGA graphics will provide better screen resolution. For best results, Super-VGA IBM 8514A compatible graphics will provide 1024 x 768 resolution and 256 colors. 8514A drivers are now available for most popular Super-VGA chip sets, and some graphics boards are hardware compatible. An accelerator card will greatly enhance screen I/O. Idrisi 4.0 takes advantage of coprocessor support, which greatly increases the processing speed of many functions. Please consult the Idrisi manuals for more information on equipment and set-up options.
Although most of the functions below have their counterparts in Idrisi for Windows, users of that system should consult the Idrisi for Windows manual for operating instructions.
(2) Since it is not possible to write to a CD, it is important to establish a working directory on read/write media (e.g., hard drive), and either copy data of interest from the CD (or on-line source) to this working directory, or access the CD directly.
(3) If using Idrisi for DOS and working from Windows 3x, 95, or NT, open a DOS shell and run Idrisi for DOS there; or restart the computer in DOS mode.
(4) From the Idrisi directory in your DOS shell (command prompt) initialize the Idrisi environment to the working directory using the ENVIRON command. Options in ENVIRON are available to set the default drive letter and working directory on disk, where you will copy the desired files (see the Idrisi manual for further instructions). Alternatively, you may set the Idrisi environment to the CD directory to access a single dataset directory in read-only mode. Note, however, that when accessing read-only files not all Idrisi functions will work because some attempt to open files in write mode.
(5) If the environment is set to a working directory on your hard drive and you wish to access resources on the CD you can set a DOS APPEND data path to the CD. The example below sets a data path to three datasets on the appropriate GED CD-ROM inserted into CD drive r:
append /e {this enables the DOS environment setting}
append r:\datasets\<dataset_directory_name>, r:\datasets\<dataset_directory_name>,
etc. -- this establishes data paths to multiple datasets.
Alternatively, copy the desired files from the CD to your working directory (recommended).
(6) You should now be setup properly. This can be tested by executing the LIST command at the DOS prompt in your Idrisi directory, resulting in a list of data layers. If this does not work, check the Idrisi environment and the DOS append path (using the DOS "set" command). If you still have trouble, see DOS APPEND.
(7) Note that any files in your working directory with the same name as those being accessed on CD via an APPEND command will be found and used first, and the appended files will be ignored.
APPEND must be initialized with the command APPEND /E prior to any other APPEND command. If the first use of APPEND does not invoke the /E option -- note forward slash -- then data paths cannot be made available to the DOS environment without rebooting DOS or the DOS shell in Windows. (Note: Do not place the APPEND /E command in the autoexec.bat or otherwise execute it if you will later start Windows, as it will cause directory problems for other Windows applications.)
If you wish to run Idrisi through Windows, do not initialize the DOS APPEND command until you are in Windows. Windows 3.0 seems to have conflicts with APPEND if it is invoked before starting Windows. Instead, enter Windows and open a DOS shell. Then initialize APPEND by typing APPEND /E (note forward slash). Then execute the desired APPEND commands. The APPEND commands should not affect other Windows applications this way, and when you close the DOS shell, the APPEND commands will be canceled.
OPERATIONS
Image Display
Download and Subset
Other functions
The following are some general comments and special notes. Please consult the Idrisi manuals for detailed information on the use of Idrisi.
Images may be viewed either "unscaled" or "autoscaled." With unscaled images, the display drivers assume that numeric values stored in the image can be directly interpreted as color codes. Thus, for example, a data value of 8 would be given color 8 (color 0 is also used for the background). If it should happen that there are not enough display colors to show the full sequence, only a subset of the data values will be displayed with instructions to press the "PgUp" and "PgDn" keys to see other subranges ("Home" and "End" keys move you to the subranges at the extremes). In other cases, such as with un-classed scalar data, you may wish to see the entire data range on the screen at once. In these instances the image must be "scaled" to fit the data range within the more limited range of available colors. This is called "autoscaling." Autoscaling is also required for viewing real number images (although the software recognizes this and will select autoscaling automatically if the image contains real numbers or negative numbers in the data range).
There is a broad range of interactive display capabilities with the COLOR display modules, including cursor/query, vector overlay, on-screen digitizing, zoom and windowing, palette change, edit, and saving, and others. Once a COLOR display option has been selected, the following key-commands can be activated:
c - cursor-query function with row/column readout
x - cursor-query function with lat/long readout
w - window/zoom feature
v - vector file overlay
p - select alternate color palette
k - edit color palette
s - saves screen or windowed image (to output directory)
d - on-screen digitizing
l - edit legend (will save to output directory)
MAP ANALYSIS
Idrisi, as with any raster GIS, realizes its greatest value in combining various digital map ('images') to characterize various user-defined phenomena. Prior to such combinations, however, there is often considerable exploration, analysis, and processing that is required to prepare each data layer. While not attempting to list all the functions available for this step, it is useful to organize a GIS session into these three steps prior to combining data layers. The Idrisi User's Guide provides a discussion of these steps (primarily under the headings, Core Modules, Geographic Analysis Modules, Statistical Analysis Modules, and part of the Image Processing Modules). Using many of these functions in Idrisi, the user can not only prepare data layers correctly, but can also produce companion layers that may help in analyzing and tracking error. It is very useful to keep a detailed list of each step in analysis and processing for later reference, and it is essential to carefully think through any anticipated series of processing steps. Most GIS, including Idrisi, are extremely flexible in what they can do, but the price of this flexibility is the ease at which apparently interesting but completely meaningless results can be generated. The power of GIS functions to avoid this is entirely in the user's hands.
If, on the other hand, one chooses to work at a coarser grid than some of the data that will be used, the problem of aggregation is introduced when accessing the finer-grid data. In this case, it is advised to first re-interpret all Datasets onto the coarser grid, using appropriate methods and documentation unique to each data set. A variety of tools should be available in Idrisi, GRASS, or other GISs to accomplish this, again, according to the user's requirements.
DATSET INTERCOMPARISON AND COMBINATION
Because of limitations in Idrisi's multiple-scale grid overlay capabilities at the time of this release, it is best for Idrisi 4.0 users to expand or contract the data files provided on CD to matching grid dimensions before undertaking any overlay, intercomparison operations, or other processing functions involving two or more data files. Since Idrisi's EXPAND and CONTRACT functions run in batch mode, this operation is relatively simple, given enough disk space in the work directory. As always, it is the user's responsibility to keep track of the true spatial meaning of the data values, regardless of the scale of representation (see note above). In general, this is best accomplished if data are expanded to the finest grid in the comparison. In this way, coarser data will be correctly represented in terms of geographical objects, even though the pixel density may be greater than needed.
A large number of intercomparison and combination functions are available in the full Idrisi implementation, in addition to those provided in the CD software. Some extremely useful functions include statistical comparisons such as REGRESS, which provides a regression analysis between two raster maps, or CROSSTAB, which gives a class-by-class tabulation; OVERLAY operations that provide algebraic combinations of two digital maps to produce a third; and other functions that access up to 12 input maps in various kinds of analyses, including classification techniques (MAKESIG, PIPED, MINDIST, and MAXLIKE), principal components analysis (PCA), cluster analysis (CLUSTER); functions in the "GIS , and others. Once again, the Idrisi User's Guide provides a detailed explanation of these combinatorial functions (including "Distance Operators," "Context Operators," "Image Classification," and portions of the "Statistical Analysis Ring").
USING SOURCE GRIDS
The source data files are similar to the other data files in format, but are provided as examples because differences in their spatial and/or temporal sampling presented problems in integrating them with the rest of the database. For example, the 8.6 minute Tateishi and Kojiware NDVI data cannot be overlain with standare 5 or 10 minute grid data even for comparative purposes without resampling one of the Datasets. Idrisi can do this using the RESAMPLE command, or, in some cases, by selecting a suitable combination of EXPAND and CONTRACT to achieve an appropriate ratio for the grid change.
TERMINATING THE SESSION
When done with Idrisi, type "APPEND ;" or reboot (close the DOS shell if in Windows) to cancel your path assignments. Other software may not work properly with an active APPEND path.
AUTOSCALING WITH FLAG VALUES
The COLOR module will include flag values in the autoscaling calculation if the flag value is within the data range (most if not all flag values should be outside the data range) or if the maximum and minimum values in the .DOC metadata file are true file max/min values (the earlier GED datasets attempted to set max/min to the data range not including flag values, but later datasets may have max/min including flag values). Idrisi's COLOR A (autoscaling) will assign the color palette to the max/min range that is specified in the .DOC file. Values outside this range will take the color of the minimum or maximum of the range, or in some cases the Idrisi color palatte may wrap to assign a color to a value that is higher than the indicated maximum.
To avoid ambiguities, you may wish to re-assign the flag values so that they will be given a unique color assignment by Idrisi.
HELP
If you have difficulties implementing Idrisi with the Global Ecosystems Database, you may contact NGDC support at the address indicated under Technical Support.