Index
GIS Issues A-Z 1st Example

Visualizing Data

DISPLAY Launcher

IDRISI is a raster-based program, so displaying images is essential for evaluating your raw data as well as intermediate products or final results by eye. Call the DISPLAY Launcher or simply press F5:

Decide which type to display - Image, Vector or Map composition file - and the dialog box presents you the appropriate fields. By default one gets into the image option. Now doubleclick (or rightbutton-click) the 'Name of file to display'-field. A Pick File list shows you all imagefile names in your working directory (remember ENVIRON) to select one.
The Expansion factor determines the size of your display window. IDRISI defaults to a value depending on the physical image size - if the raster is rather small, say 10 cols x 10 rows, you'll get an expansion factor of 64. If you like to compare many images visually, adjust that factor to your needs.
By electing a palette from the Palette options you tell IDRISI how to relate the values in the image to colors. Take one out of the already prepared or name your own palette file (visit the section about Palette files to learn more about structure, creating and handling). How IDRISI performs this relation, depends on the nature of the values: IDRISI provides you with up to 256 colors. For images with integer values ranging between 0 and 255 (byte range), IDRISI classes that value with the corresponding color code. Images holding values that extend the 0 to 255 range or those with floating point values have to be autoscaled. IDRISI checks for the minimum and maximum values, takes them as 0 resp. 255 and recalculates all the other values between as byte numbers. That's done automatically in the mentioned cases but you can force it with byte images too by clicking Autoscale image for display.
The option in the bottom part, Map components, allow you to addon descriptive elements to your map. IDRISI lets you arrange that later too.

Using the image taurvege with a palette also named taurvege:

Once you open a display, IDRISI opens a accompanying Composer dialogbox, that allows for adding/removing vector layers, modifying map components, saving and printing, thus preparing what IDRISI calls a Map Composition. Up to 16 layers can be stacked that way. One image is allowed per composition, for more use OVERLAY techniques instead. Several images side by side have to be concatenated first with CONCAT.
If you open a second display the name in the composer menu (eg. taurvege) changes to the active display window. Little icons right to the layer names tell you about the layer type. By drag and drop with that names in the composer you can alter the stack sequence. The square boxes left to the names indicate visibility. Checked means? Right - visible!
When working with bigger images (or slower CPU-speeds) it may be opportune to deactivate the Auto Redraw feature, because - well at least now at time of writing this text - display speed, especially with larger vector overlays isn't that heady.

The displayed image corresponds to a spatial database and with some simple tools you can query it interactively. If the cursor is moved over the image, column-/ row-number and the x- and y-coordinates are shown in the statusbar. To query the values, apply the Cursor inquiry mode, which must be activated from the toolbar . The cursor changes to a crosshair, and by clicking into the image IDRISI writes the cellvalues to the middle of the statusbar.

3D-Visualization with ORTHO

can be a valuable completion to 2-dimensional bird's-eye view. View direction and view angle can be adjusted between 0 - 90. Together with the TRANSPOSE module (calculates rotated images) IDRISI can produce looks from/to every direction. It allows for one byte image to be draped over the surface (normally but not compelling a DEM) and the choice of a palette:

VIEW and DUMP

VIEW
displays the cellvalues of raster files in a spreadsheet-like matrix and allows for exact cell-by-cell value identification
DUMP
is simply a binary Hex/ASCII file viewer to track your data down to byte level. It is not only useful in examining raster but all kind of data. DUMP can help checking out unknown data formats for import

Index
GIS Issues A-Z 1st Example
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