Introduction to ERDAS IMAGINE. (adapted/modified from Jensen 2004)

Transcription

1 Introduction to ERDAS IMAGINE General Instructions (adapted/modified from Jensen 2004) 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. 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. 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. 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. 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: Learn how to open the ERDAS IMAGINE Preference Editor and set preferences 1 of 10

2 Display different types of data formats and make simple measurements on the image 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. 2 of 10

3 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 All Programs Leica Geosystems GIS & Mapping 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 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)? 3 of 10

4 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 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. 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. 4 of 10

5 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? 5 of 10

6 Task Three: Examining Cursor, Magnification, and Overlay Operations Information about the images used in this exercise: File Name cola_tm_ img Location Columbia, SC cola_atlas_ img Columbia, SC 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 ( ) Band 2 = Red ( ) Band 3 = NIR ( ) Band 1 = Blue ( ) Band 2 = Green ( ) Band 3 = Red ( ) Band 4 = NIR ( ) The next image we will browse is a Landsat Thematic Mapper (TM) scene of Columbia, SC. Open the file cola_tm_ 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. 6 of 10

7 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. Urban b. Water c. Forests d. 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_ 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 7 of 10

8 Task Four: Spectral and Spatial Profile Tools Information about the image used in this part: File Name isle-of-palms_atlas_ img Location Isle of Palms, SC Sensor Airborne Terrest. Applications Sensor (ATLAS) Spatial 2.5 x 2.5 m Temporal October 15, 1998 Spectral Band 1 = Blue ( ) Band 2 = Green ( ) Band 3 = Red ( ) Band 4 = NIR ( ) Band 5 = NIR ( ) Band 6 = MIR ( ) Band 7 = Thermal ( ) 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_ 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 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 Y- axis 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. 8 of 10

9 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? 9 of 10

10 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_ 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_ 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. band sequential (BSQ) b. band interleaved by line (BIL) c. band interleaved by pixel (BIP) d. run-length encoding 10 of 10