Geography 243 - Remote Sensing
Lab Activity 1: Exploring Idrisi32
This lab activity will introduce you to the Idrisi system, providing a quick tour of the main functions we will be using this term. The data we will use is in a zipped (compressed) folder that you can download and unzip using the in-class application 7-Zip. When you have uncompressed this folder place it on your desktop or better yet your flash drive and add your name to the folder name. If you want to save your work you will need to set this folder on your flash drive as the Main Working Folder. In this activity you may work in groups of a size > 1 (one) and < 3 (three). Find a partner and get started.
What you will need:
The image files we are working with in this activity are Landsat Thematic Mapper images that have been georeferenced to the Universal Transverse Mercator coordinate system. They cover a large area of a particular Midwestern city.
Begin by opening Idrisi. This is accessed through the START-ALL PROGRAMS-IDRISI32 route. When the application has started it presents a simple interface. At the top of the screen you will see the menu bar:
These present pulldown menus that give you direct access to virtually all the functions that can be accessed in the button bar below. In addition access is provided here to many other modules that greatly extend the system's power to accomplish advanced spatial analysis. Below the menu bar is the button bar:
Each of these will be taken in sequence and explained briefly .
Data Paths/ Project
Environment
This module is used to set the location of the data files (images, vector files, etc.) and other system resources. Use the "New Project..." button to create a project file that will contain all of the settings you change as you work on these images. This file should be given a logical name and stored in a safe location (your flash drive). Use this module to browse to the location of the folder that we are using for this lab (see above) and set this as the project folder.
File Explorer
The Idrisi File Explorer provides an environment for managing and viewing Idrisi files. Use this utility to:
Use this tool to look over the files in your project folder.
METADATA is used to create, view and edit documentation files accompanying IDRISI
raster, vector and attribute values files. It is also used to create, view and edit
Reference System Parameter Files. This can be useful for learning things about
the image files we are working with.
Display
DISPLAY LAUNCHER is the module that allows you to open a new display window. It begins the map composition process and is always the first operation required to create a new map display. Options allow you to display an existing map composition, or to begin a new composition by displaying either a raster layer or a vector layer. As soon as a map layer is displayed, several buttons on the tool bar become functional. Use this to display each of the raster files in your project folder using several of the available palettes. When a new display window is opened the MAP COMPOSER window is also opened:
Use this dialog to complete common map composition tasks, zoom and recenter the image, change map properties and add other layers to the image/map. This is where you can add additional layers to your composition. Since we are working with images from 1992 and 2000 in this activity it will be interesting to add layers from both of these dates and compare the two images to identify locations where significant changes have taken place. You can toggle the images "on" or "off" using the red check to the left of the layer in the COMPOSER window to be able to see this effect. The "Layer Properties" button opens an important dialog:
This is used to set the parameters of a particular layer that you are working with. The histogram button produces a histogram of the brightness values for the image layer that you are exploring. This can be very useful when analyzing the image. The slide bars at the bottom of the screen can be used as an interactive image stretch tool. Explore this dialog...
Symbol
Workshop
SYMBOL WORKSHOP is used for the creation and editing of IDRISI symbol and palette
files. These files record the graphic renditions for up to 256 symbols. There are five
different types of symbol files supported by IDRISI: point, line, polygon, text and
palette symbol files. Internally these are identified by files with ".sm0",
".sm1", ".sm2", ".smt" and ".smp", extensions
respectively. This will be useful later so it is a good time to explore the capabilities
of this workshop.
Palette
Workshop
This module allows you to access and modify Idrisi Palette files. Again this may be useful later - explore it.
Stretch
STRETCH rescales image values to fall within a range from the data values (or
user-defined) minimum to a user-specified upper limit as preparation for DISPLAY LAUNCHER.
We'll be using this later.
Color
Composite
COMPOSITE produces a color composite image from three bands of byte binary imagery.
24-
and 8-bit composites may be produced. The former is used for display and visual analysis,
while the latter is used primarily as input to the CLUSTER and ISOCLUST modules.
This module allows you to produce visually stunning images that are in-effect false
color composites of the satellite image data.
Fit Map
to Layer Frame
The layer frame is the "box" in which all map layers are placed. If the layer frame is resized and the resulting frame is smaller than the underlying map area, scroll bars will appear. You can now move around the image with these bars. If you resize the layer frame and would like to also resize the map window snug to the layer frame, use the Fit Map Window to Layer Frame icon on the toolbar.
Maximize Layer Frame
To make the layer frame as large as possible, use the:
Maximize display of layer frame toolbar icon
End key on the keyboard (leaves room for Composer)
Shift+End keys on the keyboard (does not leave room for Composer)
Zoom
Window
The Zoom Window tool allows you to drag a box around an area to zoom into. The layer
frame will remain the same size and the area you identified will be displayed as large as
possible in the layer frame. To do so, simply click on the ZOOM WINDOW icon on the
toolbar. Then, as you move the mouse over any map window layer frame, you will notice that
the cursor looks like a box. Place the arrow at one corner of the region of interest.
Click the left button and hold it down while you drag the cursor to the diagonal corner to
define the region (you will notice a rectangle being formed that will define the region
that will be windowed). When you release the left button, the zoom window will take
effect. Each time you wish to use the Zoom Window tool, you must click it on the toolbar.
You can zoom into a display that is already zoomed. However, you will probably wish to
restore your layer frame to the original view at some point. To do so, be sure the map
window you wish to restore to size has focus, and then click the Restore Original Window
icon on the toolbar.
Restore Original Window
To restore the original display, use the Restore Original Window Icon (Home key on the
keyboard.)
Collection
Linked Zoom
To navigate more than one display in the same way, first create a collection for all the members with the Collection Editor. Then display the collection members with their full “dot-logic” filenames. Click on the Collection Linked Zoom icon on the toolbar. While this icon is depressed, any navigation command carried out in one display window will be mimicked in all other windows that belong to the same collection. For example, if you have all the bands of a satellite scene in a raster group file (created with Collection Editor) and have them displayed on the screen. When you click the Collection Linked Zoom icon and zoom into one image with the Page Down key or the Zoom Window tool, all the displayed images will also zoom in the same way. To turn off this mode, click the Collection Linked Zoom icon again.
Placemarks
Placemarks may be thought of as spatial bookmarks. Each identifies a region. By
defining placemarks, you can easily return to particular zoom views. On the left side of
the dialog is a list of placemarks. Your options include: add current view as a new
placemark, change the name of selected placemark, delete the selected placemark, or go to
selected placemark. If you are adding a new placemark or changing the name, enter the name
in the input box provided. This tab may also be activated from the Placemarks icon on the
toolbar. Up to ten placemarks can be defined.
Placemarks are only saved when the map display is saved to a MAP composition file from the
Save Composition option in Composer.
Cursor Inquiry
As you move your mouse over a map window, the X and Y coordinates of that location in the underlying geographic reference system are reported in the status bar at the bottom of the screen. (If the map window includes a raster image, the column and row position is also shown.) You can also obtain information on the value of any cell within a raster image layer or the attribute of any vector feature by activating cursor inquiry mode. To do so, be sure that the window you wish to query has focus and the layer you wish to query is highlighted in Composer. Then click on the CURSOR INQUIRY icon. When this mode is activated, the icon will appear depressed and as you move around the display, the cursor will be in the shape of a crosshair. Click on the left mouse button to inquire of the value at any position. It will be shown nearby. If legend captions exist in the documentation file, the corresponding caption will also be shown. It is nearly impossible to click directly upon vector lines and points. When querying these layers, the feature that is nearest to the cursor position is selected and the attribute is reported. For all vector layers, the selected feature is shown in red. To stop using interactive inquiry, click on the CURSOR INQUIRY icon again.
Feature Properties
The Feature Properties button on Composer activates the feature properties
query tool which allows for cursor query across multiple layers. This may also
be activated with the Feature Properties icon on the toolbar. Note that when
Feature Properties is active, the cursor inquiry icon is also activated. When
Feature Properties is activated, a table will open in a window below Composer.
If you are querying a collection, the left column lists the layer names and the
right column lists the queried attribute values. To query values across multiple
raster images, first create a raster group file with the Collection Editor. Then
display one group member with its full “dot-logic” name with Display Launcher. When you click anywhere in the image, the value at that
location in all seven bands is shown in the Feature Properties table.
Similarly, you can query values for several fields of a database associated with a vector
layer. First use the Collection Editor to create a Vector Link file. Display one of the
collection members as described above. Invoke the query tool. The values for all the
fields in the collection will be displayed in the Feature Properties box.
The Toggle Graph Option of Feature Properties allows you to change the display of the
attributes from the actual values to a bar graph representing those values. When the
graphic display is activated, you may choose to use either independent or relative
scaling. With independent scaling the length of the bar is proportional to the range of
values in that data layer. With relative scaling, the length of the bar is proportional to
a range that is set in the Graph Limits dialog. See Graph Limits for details.
If you use Feature Properties on a layer that is not a collection member, the row, column,
x and y coordinate, as well as the attribute value for that location will be displayed in
the Feature Properties table.
Digitize
DIGITIZE provides the ability to digitize on screen. Point, line, polygon and text vector layers may be created.
Delete
Feature
You can delete completed vector features at any time. To do so, first highlight the vector layer containing the feature on Composer. Click on the Delete icon. The cursor then becomes a pointing finger when moved over the layer frame. Click on the feature to be deleted to highlight it, then press the Delete key to delete the feature from the file. You may perform this operation on any vector layer, even if it is not being currently used with on-screen digitizing.
Save
Digitized Data
As you digitize features, they will each in turn be added to the vector layer data file. In order to save this file click on the Save Digitized Data button. You may then stop digitizing or add more features to the vector file.
GPS Link
IDRISI has the ability to use a Global Positioning System (GPS) receiver as an input device. Input is to the active display and may optionally be saved as a vector point or line file. This is typically used in conjunction with field work such as ground-truthing or training site selection. To be used with IDRISI, the receiver must be capable of outputting data to an RS232C serial port in National Marine Electronics Association (NMEA) format.
Histogram
Display
HISTO produces a frequency histogram of cell values in an IDRISI image. HISTO creates histograms by dividing the data range into classes of a user-specified width. The frequency within each class is tabulated. Both graphic and numeric output options are available. HISTO also outputs basic statistics about the file.
Ortho Surface
Display
ORTHO displays and prints three-dimensional orthographic perspective displays of IDRISI images. Normally the images displayed are surfaces, although any IDRISI image may be viewed with this routine. A second image may also be draped onto the top of the surface displayed.
Edit
EDIT provides an ASCII text editor for creating and editing text files.
Database Workshop
DATABASE WORKSHOP provides IDRISI with an integrated relational database management
system. While it is not meant to replace an independent database management product, it
does provide an extensive set of capabilities including the ability to:
- read database files in ACCESS, and xBASE formats
- create database files in Microsoft ACCESS format
- add or delete fields
- filter the database using Structured Query Language (SQL)
- calculate expressions based on Structured Query Language (SQL)
- find specific records
- link the database to the map display
- create Boolean and autoscaled continuous display output
- export field values to attribute values files for use with ASSIGN
- import attribute values files created with modules such as EXTRACT
DATABASE WORKSHOP provides the ability to create, edit and analyze database files in
IDRISI. It is important to recognize that this capability is integrated with the IDRISI
system. From the perspective of IDRISI, database files are simply another form of values
files, and thus carry a documentation file just like any other values file. If it doesn't
already exist, a documentation file is automatically created when a database table is
opened in DATABASE WORKSHOP.
Image
Calculator
IMAGE CALCULATOR is an interactive expression-building module which encapsulates the functionality found in the modules OVERLAY, SCALAR ,TRANSFORM and part of RECLASS. For the most part, operations undertaken with these modules can be performed in IMAGE CALCULATOR with considerably less effort and without the use of macros. There are two types of operations which are supported by IMAGE CALCULATOR. These are Mathematical Expressions and Logical Expressions. Expressions can be edited by typing into the expression editor directly from the keyboard, or can be produced using the mouse to click one of two "keypads."
Reclass
RECLASS classifies or reclassifies the data stored in images or attribute values files into new integer categories. Classification or reclassification is by equal intervals division of the data range, or by the application of user-defined limits.
Overlay
OVERLAY produces a new image from the data of two input images. New values result from applying one of the nine possible operations to the two input images, referred to as the first and second images during program operation.
Work through each of these functions exploring the images and vector layers in your
project folder. Make certain to try all functions, in particular the image COMPOSITE
function
to create several 24-bit composites and make sure you fully explore the MAP COMPOSER
window. Make certain that you understand how each module works and what
its purpose is before you move on to the next (I recommend taking notes on each
module that describe what it does and how it works). Use the COMPOSITE function to produce a 3-channel composite view of the
city. Remember to make your composite image using channels all from one
date or the other - if you combine the channels from different dates using this
dataset it WILL make an image but it WON'T look very good. This is a result
of these files being different sizes causing them to be out of registration -
this is something you can explore in the Metadata
section. Later in term we'll see how to register images from different
dates. When you have a color composition that you feel best displays the character of
the dataset, or one that you are happy with, use the PRINT COMPOSITION module in
the composer to print your composition on the Designjet color plotter. To finish
you should have the following parts completed:
Aces!! This activity is due at the end of the class Tuesday, April 14.
