Objective
- To introduce basic ERDAS IMAGINE display and screen cursor control procedures.
Part I - Introduction to ERDAS IMAGINE
During this semester, we will be using ERDAS IMAGINE 8.7 image processing and GIS software for Windows XP. IMAGINE 8.7 is a product of ERDAS LLC, a recently acquired subsidiary of Leica Geosystems. The latest versions of IMAGINE are designed to complement ESRI's ArcGIS software.
We will be analyzing four images in this exercise. Follow the directions given to you in class to login to the system. The imagery that you will work with this week is currently available from this webpage. When you download the imagery, please use "Save Target As..." function by clicking the right-button of your mouse. You can download the imagery to your MAPTUBE space or any other place you want to save it. However, when working in the lab, copy the files you need to your local machine to optimize data access speed.
After you have successfully logged onto the system, launch IMAGINE by going to the Start Menu - Remote Sensing - ERDAS IMAGINE 8.7. Wait a few seconds for all menus to appear. Examine the icon panel along the top of the screen. These icons represent the various components and add-on modules available with the University's current license. You have the option of displaying the icon panel horizontally across the top of the screen or vertically down the left side of the screen using the [Session | Flip Icons] menu item.
Familiarize yourself with the five menu
items located along the top of the icon panel in the left corner: [Session], [Main],
[Tools], [Utilities], & [Help]. The Session menu controls many of the session
settings such as user preferences and configuration options. The [Main] menu allows
access to all the modules located along the icon panel. The [Tools] menu allows
you to display and edit annotation, image, and vector information, access surface
draping capabilities, manage post script and true type fonts, convert coordinates,
and view Erdas Macro Language (EML) script files. The [Utilities] menu
allows access to a variety of compression and conversion algorithms including
JPEG, ASCII, image to annotation, and annotation to raster. The [Help] menu brings
up the IMAGINE On-Line Documentation documentation as well as icon panel
and version information. An index of keywords helps you to quickly locate a help
topic by title. A text search function also helps you find topics in which a word
or phrase appears. The menu you will probably use
the most under the [Session] menu is the Preference Editor. The Preference
Editor is accessed under [Session | Preferences]. It allows you to customize
and control many individual or global IMAGINE parameters and default settings.
Use the left mouse button (lmb) on the scroll arrows on the side of this menu
to examine the available categories. With the User Interface & Session
category open, change the Default Data and Output Directories to
whatever you like (for example):
c:\Temp\Ex02
Save these changes using the [User Save] or
[Global Save] buttons and close the editor. Proper use of these preferences can
reduce the time it takes you to perform image processing tasks.
Part II - Image Display
Image
| File Name | marco-island_spot_1988-10-21.img | Quick View |
|---|---|---|
| Location | Marco Island, FL |
 Altitude 832 km |
| Sensor | SPOT XS | |
| Spatial | 20 x 20 meters | |
| Temporal | 21 October, 1988 | |
| Spectral (micrometers) | Band 1 = Green (.50-.59)
Band 2 = Red (.61-.68) Band 3 = NIR (.79-.89) Band 4 = Panchromatic (.51-.73) |
Now you are ready to display the first image. Move the cursor back to the IMAGINE Viewer and select the File dropdown menu with the lmb. Select [File | Open | Raster Layer] to get to the Select Layer to Add: dialog. You can also type [Ctrl R] or click on the Viewer icon that looks like a manila folder that is half open to accomplish the same task. Additional Viewers may be opened by clicking the [Viewer] icon on the IMAGINE icon panel.
On the left side of the menu you should see a list of files in the current folder. Navigate to the desired folder if necessary. Position the cursor over the file you want to display (e.g. marco-island_spot_1988-10-21.img) and click the lmb once (do not double-click). The file name should appear in the file name window in the Viewer. If you do not see the correct files then you are either not looking in the correct folder or you do not have the [Files of type] specified as IMAGINE Image (*.img).
Before clicking [OK], you need
to assign the spectral bands of the image to the color planes red, green,
blue (RGB). Click on the [Raster Options] folder tab and assign band 3 (NIR)
to red, band 2 (Red) to green, and band 1 (Green) to blue. Make sure that
the [Display] option is set to [True Color] . You also have the option of
making the image fit the Viewer frame by depressing the small box
next to Fit to Frame. Now you are ready to click [OK]. If the SPOT
image is requiring less space in the IMAGINE Viewer (there are large
black borders on the sides) then you can resize the IMAGINE Viewer
to use your screen desktop area more efficiently. This will become important
in future exercises when many IMAGINE Viewers will need to be open
at once. To remove an image displayed in the IMAGINE Viewer move
to the [File] dropdown menu in that Viewer and select it with the
lmb, then find the [Clear] option and select it. You can also click on the
Close Top Layer or Eraser tool icons in the Viewer.
To find out additional information about this image, go to the [Utility] drop down menu in the open Viewer. Choose [Layer Info] and wait for the ImageInfo dialog box to appear. You can also access ImageInfo by clicking on the "info" icon in the Viewer icon menu (third one from the left). Now answer the following questions:
1a) What is the pixel size in the X and Y direction?
1b) What are the units of measurement?
1c) What map projection is the image georeferenced to?
1d) What is the maximum brightness value indicated in the Statistics Info for the green band?
1e) What is the minimum brightness value indicated in the Statistics Info for the red band?
1f) Print out the histogram for the NIR band and explain the reason for the bi-modal distribution.
1g) Examine the Map Info contents in the panchromatic band. Can you identify any errors?
Now exit the ImageInfo dialog box by choosing [Close] under the [File] drop down menu and return to the IMAGINE Viewer #1. Select the [Three Layer Arrangement] under the [Open] option. Choose marco-island_spot_1988-10-21.img as the IMAGINE file to display once again. In the [Options] folder, set the display as [True Color] and set the [Layers to Color] equal to Red = 3, Green = 2, and Blue = 1 (RGB = 3, 2, 1) and click [OK]. This will open the color composite in Viewer #1 and each of the individual bands in grayscale mode in three other viewers.
Now position the cursor over the Viewer and press the right mouse button (rmb) to access the [Quick View] menu. Examine the options and move the cursor over [Fit Image to Window] and select it. The [Quick View] menu should then disappear. This will affect only the Viewer you are currently using. For other Viewers you will need to repeat the process. You can additionally use the [View | Fit Image to Window] command to achieve the same result. An Area of Interest (AOI) Box should have appeared in Viewer #1 and is geolinked to the other three Viewers. With the Reset Window Tools icon selected, the AOI Box can be dragged around and resized for simultaneous band comparison and analysis. When you are finished answering the following questions, close the other Viewers by selecting [File | Close Other Viewers] in the Viewer #1 menu.
2a) What would be some advantages of having multiple viewers open when working with a large research project?
2b) Compare each of the three grayscale bands (green, red, and NIR) and briefly describe how they differ in their spectral responses to terrestrial features.
2c) If you wanted to study the road network of Marco Island, which one of the three image displays (green, red, and NIR) would be best? Why?
Part III - Cursor, Magnification, and Overlay Operations
Images
| File Name | cola_tm_1991-1-15.img | Quick View | cola_atlas_1997-10-7.img | Quick View |
|---|---|---|---|---|
| Location | Columbia, SC |
 RGB=4,3,2 Altitude 705 km |
Columbia, SC |
 RGB=4,3,2 Altitude 5000 ft AGL |
| Sensor | Landsat TM | Airborne Terrestrial Applications
Sensor (ATLAS) |
||
| Spatial | 30 x 30 m | 3 x 3 m | ||
| Temporal | 15 January, 1991 | October 7, 1997 | ||
| Spectral | Band 1 = Green (.52-.60) Band 2 = Red (.63-.69) Band 3 = NIR (.76-.90) |
Band 1 = Blue (.45-.52) Band 2 = Green (.52-.60) Band 3 = Red (.63-.69) Band 4 = NIR (.76-.90) |
The next image we will browse is a Landsat Thematic Mapper (TM) scene of Columbia, SC. Open the file cola_tm_1991-1-15.img the same way you opened the first image and assign Red = Band 3 (NIR), Green = Band 2 (red), and Blue = Band 1 (green). Make sure you click the [Fit to Frame] box before opening it, or you can fit the image to the viewer using the QuickView menu.
To magnify (or reduce) an image, the easiest option is to use the Interactive Zoom In (or Interactive Zoom Out) tools that are located immediately above the image in the gray Viewer area. The area over which you place the cursor will be the general center for the area that is magnified. However, you may at some times wish to magnify the image by a certain factor, such as 2X or 4X. To do so you can select [Zoom] under the [View] menu or [Quick View] menu and then select the appropriate choice. When you choose Zoom in by X or Zoom out by X you can also choose the interpolation method. These methods will be evaluated in class at a future time, but you might wish to try each method for the sake of understanding them. When you have completed your selection click [OK] and the magnified image will appear. Another method of explicitly specifying the zoom factor is under the [Raster Options] feature when you open a file. When [Fit to Frame] is not highlighted, you can enter in the [Zoom by] factor in the lower left hand corner. Finally, you also have the ability to change the frame scale of the image. The process can be implemented using the [View | Scale] option. The icon with the hand also gives you panning capabilities within the Viewer.
You can also create a magnifying window by either choosing [View | Create Magnifier] or accessing the [Quick View] menu and selecting [Zoom | Create Magnifier]. This brings up an additional window that corresponds to the AOI Box in your Viewer. The AOI Box can be resized by dragging on the corners. To close the magnifier, place your cursor inside it and select the [Close Window] option in the [QuickView] menu.
Sometimes it is necessary to determine the coordinates and brightness values of specific pixels in the displayed image. The inquire cursor allows you to do this. Go into the [Quick View] menu of the IMAGINE Viewer and select [Inquire Cursor]. This will open a pixel information menu that allows you to move a crosshair cursor on the Viewer. You can use the black arrows to move the crosshair cursor in any pixel increment you set. For now leave the increment at 1.00 and note that the increment is variable between the file and map coordinate system. You can move the crosshair cursor using the black arrows or by pressing and holding the lmb while the mouse cursor touches the crosshair cursor. For "fine tuning" use the keyboard arrows to move the cursor. The black circle will move the crosshair cursor back to the center of the Viewer.
Reference system values for the image can be obtained in either Map, Paper, File, or Lat/Lon, or MGRS coordinates. Notice that the coordinate system is defined for you. The image projection is also shown but if you have not selected the Map option then you may not necessarily be viewing the x, y coordinates of that projection system. The table shows the R,G,B pixel brightness values for both the image file (File Pixel) and the color lookup table (LUT Value). Move the Viewer Cursor and notice how the values change. To move the Inquire Cursor using the mouse you must initially place the arrow cursor at the center of the crosshairs and click on the lmb. Keep the lmb depressed to move the Inquire Cursor.
3a) Which of the coordinate systems would you use to describe a pixel location to someone working on a different dataset? Why?
3b) Position the crosshairs on a representative pixel and record the actual data values in each band for the following features:
a. Urban
b. Water
c. Forests
d. Grass
3c) How do these data values compare with your knowledge of the spectral signatures for urban, water, and vegetation?
Now close the Inquire Cursor dialog and
open another image in Viewer #1 without closing the TM
scene. You can use IMAGINE to overlay imagery that is georeferenced
to the same coordinate system. To do this, be sure to uncheck
the [Clear Display] option under Raster in the [Select
Layer to Add] dialog box. Now overlay the file
cola_atlas_1997-10-7.img
on top of the TM scene using RGB=4,3,2. This scene is a higher
spatial resolution (i.e. 3 x 3 m instead of 20 x 20 m) image
of downtown Columbia. Now zoom in to the downtown area and experiment
with the utilities listed below.
4a) Using the [Utility | Measure] tool, what is the perimeter and total area of the Coliseum?
4b) Briefly discuss how these utilities could be useful to an image analyst:
a. Utility - Blend
b. Utility - Swipe
c. Utility - Flicker
A natural color composite of the downtown scene can be viewed by selecting [Raster | Band Combinations] and changing the RGB values to RGB=3,2,1. This is the way humans would view the scene if looking down from a plane.
