Introduction to ERDAS IMAGINE

Exercise One
Introduction to ERDAS IMAGINE
(adapted/modified from Jensen 2004)
General Instructions
¾ Follow the directions given to you in class to login the system. If you
haven’t done this yet, create a folder and name it with your last name
once you login. Move into this folder and create another new folder
named “RS labs.”
¾ During this short course, 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 subsidiary of Leica Geosystems. The latest
versions of IMAGINE are designed to complement ESRI’s ArcGIS
software.
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¾ ERDAS IMAGINE has an On-Line help system that is arranged in
several manuals. When you click on the Help button in a dialog, you
are taken directly to the Help for that dialog. That Help file is within a
manual. The manual name appears in the title bar of the Help window.
You can open any manual and view its contents by clicking the
Contents button in the Help menu bar. Browse through this manual for
more information about how to use the Help system. It is very
important that you become familiar with the help system as you may
wish to refer to and learn how to get around during the course of the
exercise.
¾ As you work through this lab, you will be asked several questions.
Write your answers in a Word Doc file and submit your answer report
upon the end of today’s class.
¾ When you have finished your assignment, follow the directions listed
below for ending an IMAGINE session. Hand in your typed answers to
each of the questions, as well as any requested graphs
*
o
From [Session] menu choose the [Close All Viewers] option.
o
From [Session] menu select [Quit].
o
Logoff from your machine.
In this investigation, you will to familiarize yourself with using the ERDAS
Imagine system for displaying imagery and examining spectral response of
ground features. Specific objectives include:
n
Learn how to open the ERDAS IMAGINE Preference Editor and set
preferences
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Exercise One
o
Display different types of data formats and make simple
measurements on the image
p
Examine overlay operations
[
Query for image information and spectral information
\
Understand common data storage formats
We will be analyzing a number of images in this exercise. The imagery that
you will work with in this exercise is currently available under a folder called
“RS Data” under the Z: Drive. Under this folder you will find a self extracting
zip file called “RS-Exercise1.exe.” Double click on the files and "Save As..."
the files into the “RS labs” folder you created under your folder. A new folder
called “RS-Exercise1” will be created.
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Exercise One
Task One: Setting up preferences in ERDAS Imagine
After you have successfully extracted “RS-Exercise1” onto your folder, launch IMAGINE
by going to the Start Menu Î All Programs Î Leica Geosystems GIS & Mapping Î
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 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 Î Preferences]. It allows you
to customize and control many individual or global IMAGINE parameters and default
settings. Use the left mouse button 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 your own folders as follows:
Default Data Directory: z:/…/your directory/RS labs/RS-Excerise1
Default Output Directory: z:/…/your directory/RS labs/RS-Excerise1
Temporary File Directory: $TEMP
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.
1. What is the default band to color gun combination for Landsat TM data (i.e.,
what are the default bands assigned to each of the red, green, and blue
color guns)?
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Exercise One
Task Two: Displaying images and viewing information
Now you are ready to display the first image. Move the cursor back to the IMAGINE
Viewer and select the File dropdown menu. Select [File Î Open Î 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. Position
the cursor over CBD-Cairo.img, this is a QuickBird Image for downtown Cairo, and
click the left mouse button 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 (RED) to red, band 2 (Green) to green, and band 1 (Blue) 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 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 left mouse button, then find the [Clear] option and select
it. You can also click on the Close Top Layer or Eraser tool icons in the Viewer.
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Exercise One
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 "i" icon in the Viewer icon
menu (third one from the left). Now answer the following questions:
2. What is the pixel size in the X and Y direction?
3. What are the units of measurement?
4. What map projection is the image georeferenced to?
5. What is the maximum brightness value indicated in the Statistics Info for
the green band?
6. What is the minimum brightness value indicated in the Statistics Info for
the red band?
7. Print out the histogram for the NIR band (layer 4) and explain the reason
for the bi-modal distribution.
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 CBD-Cairo.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 = 4 (InfraRed), 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 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.
8. What does RED color represent on the urban scene? Why?
9. What would be some advantages of having multiple viewers open when
working with a large research project?
10. Compare each of the three grayscale bands (green, red, and NIR) and
briefly describe how they differ in their spectral responses to terrestrial
features.
11. If you wanted to study the road network of downtown Cairo, which one of
the three image displays (green, red, and NIR) would be best? Why?
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Exercise One
Task Three: Examining Cursor, Magnification, and Overlay
Operations
Information about the images used in this exercise:
File Name cola_tm_1991-1-15.img
Location Columbia, SC
cola_atlas_1997-10-7.img
Columbia, SC
Sensor
Landsat TM
Airborne Terrestrial Applications
Sensor (ATLAS)
Spatial
30 x 30 m
3x3m
Temporal 15 January, 1991
October 7, 1997
Band 1 = Blue (.45-.52)
Band 1 = Green (.52-.60)
Band 2 = Green (.52-.60)
Spectral Band 2 = Red (.63-.69)
Band 3 = Red (.63-.69)
Band 3 = NIR (.76-.90)
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.
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Exercise One
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 left mouse button 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 left mouse button.
Keep the left mouse button depressed to move the Inquire Cursor.
12. Which of the coordinate systems would you use to describe a pixel
location to someone working on a different dataset? Why?
13. Position the crosshairs on a representative pixel and record the actual
data values in each band for the following features:
a.
b.
c.
d.
Urban
Water
Forests
Grass
14. 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.
15. Search the internet for information about “Carolina Coliseum” then lthe
Coliseum on the image and use the [Utility | Measure] tool to determine
the perimeter and total area of the Coliseum?
16. Briefly discuss how these utilities could be useful to an image analyst:
a. Utility - Blend
b. Utility - Swipe
c. Utility - Flicker
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Exercise One
Task Four: Spectral and Spatial Profile Tools
Information about the image used in this part:
File Name isle-of-palms_atlas_1998-10-15.img
Location Isle of Palms, SC
Sensor
Airborne Terrest. Applications
Sensor (ATLAS)
Spatial
2.5 x 2.5 m
Temporal October 15, 1998
Band 1 = Blue (.45-.52)
Band 2 = Green (.52-.60)
Band 3 = Red (.63-.69)
Spectral Band 4 = NIR (.76-.90)
Band 5 = NIR (1.55-1.75)
Band 6 = MIR (2.08-2.35)
Band 7 = Thermal (10.2-11.2)
For this part of the exercise you will examine an image of estuary marshland of
smooth cordgrass near Isle of Palms, SC. We will be using the spectral and spatial
profile tools for the analysis. Open the image isle-of-palms_atlas_1998-10-15.img
with RGB = 4,3,2. When the image is displayed, click on the [Start Profile Tools] icon
(next to the "hammer" icon) in the Viewer toolbar as shown in the figure below:
Another way to access the Profile Tools is to go to [Raster Î Profile Tools] in the
Viewer menu bar. Select [Spectral] and click [OK]. After the Spectral Profile tool
appears, click on [Edit | Chart Options]. Now click on the Y-axis folder and change Yaxis maximum value to 80.0 and click [Apply], then close the Chart Options dialog
box. Using the crosshair icon, place three spectral profile points at the file
coordinates listed below. To do this, first randomly drop the point in the image and
then type in the x, y file coordinates.
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Exercise One
17. Print the Spectral Profile plot of all three points listed below and briefly
explain the spectral curve difference of each point as it relates to the
electromagnetic spectrum. You may want to zoom in on the individual
points for a more detailed analysis.
a. 242, 470 (Healthy Cordgrass)
b. 272, 508 (Water)
c. 302, 504 (Oyster Bed)
Now open the Spatial Profile tool by clicking on the [Start Profile Tools] icon in the
Viewer toolbar or go to [Raster | Profile Tools] in the Viewer menu bar. Select
[Spatial] and click [OK]. When the Spatial Profile tool appears, change the Y-axis in
the chart to 80.0 and click on the polyline icon (next to the cursor icon). Draw a
polyline on the image in the Viewer. Single-click to set vertices and double-click to
set an endpoint. The default is to view one band at a time. View different bands by
incrementing the Plot Layer option up or down to the band you want to view. To view
multiple bands simultaneously in the profile chart, select [Edit | Plot Layers] in the
Spatial Profile Tool. When the Band Combination dialog opens, add the layers you
want to view by selecting each band one at a time and clicking on the [Add Selected
Layer] icon (top icon). Then click [Apply] and close the dialog. Now briefly answer the
remaining questions:
18. Cordgrass is known to grow very densely at the edges of inlet rivers
and less densely as further away from the river. Draw a profile line on
the image that illustrates this point using three of the seven bands and
print the graph. Describe the general trends of the changes in data
values in the above graph using your knowledge of spectral signatures
and explain why the values change as they do.
19. Based on your analysis, what band do you think would be most
sensitive to the evidence of smooth cordgrass biomass and why?
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Exercise One
Task Five: Data Formats and Import/Export
In remote sensing applications, we frequently use images in formats other than
IMAGINE (*.img), such as the LAN (*.lan) format. The ".lan" suffix signifies that the files
were created using a previous version of IMAGINE (e.g. IMAGINE 7.5). The images
must be imported into Imagine 8.5 and converted to IMAGINE (*.img) format before we
can begin to process them. Directions for doing this are found below.
Find and select the Import button on the main icon panel.
When the Import/Export dialog box appears, do the following:
Make sure the [Import] option is selected.
Specify Type as [LAN (Erdas 7.x)].
Specify Media as [File].
Now select murrells-inlet_cams_1997-08-02.lan as the input file.
After you have specified the Input File (*.lan), a filename with the same prefix but with an
IMAGINE (*.img) extension should automatically appear in the Output File (*.img)
column. Make sure the file is going to be written to the correct directory, select [OK] and
wait for another window to appear. We will not be modifying the image during the import
process but, there are some options menus that you may wish to look at, especially the
Import Options (where you can layer stack selected individual bands).
When you are ready to import the image, select [OK]. When the import job has
completed, select [OK] from the job state window.
Now display the newly imported murrells-inlet_cams_1997-08-02.img file in the viewer
with RGB = 6,4,2. This equates to placing the NIR band (6) in the red image plane, the
red band (4) in the green image plane, and the green band (2) in the blue image plane.
20. Briefly describe (you may want to use simple illustrations) the logic and
differences between the four common generic binary data storage formats
and any advantages/disadvantages of each including:
a.
b.
c.
d.
band sequential (BSQ)
band interleaved by line (BIL)
band interleaved by pixel (BIP)
run-length encoding
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