CEE 6150 Remote Sensing Fundamentals
Lab #1: Introduction to ENVI
Introduction to ENVI
Start ENVI from the START Menu
1
(Adapted from RSI Introductory Tutorial for ENVI.)
.
Select All Programs Class Files ENVI 5.0 Tools ENVI Classic.
ENVI uses a graphical user interface (GUI) to provide point-and-click access to image processing functions.
You select menu choices and functions using a three-button mouse.
If you are using ENVI for Windows with a two-button mouse, you can simulate a "middle" mouse button press
by holding down the Control key and pressing the left mouse button.
Figure 1: ENVI Main Menu
When you start ENVI, the ENVI Main Menu appears in the form of a button menu bar (Figure 1). Clicking with
the left mouse button on any of the Main Menu buttons brings up a menu of options, which may in turn contain
submenus with further options. The choices selected from these submenus will often bring up dialog boxes that
allow you to enter information or set parameters relating to the ENVI function you have selected.
Note that most menus in ENVI windows and dialog boxes appear as buttons. Often the button label changes to
reflect the currently-selected menu option.
OPEN AN IMAGE FILE
To open an image file:
•
Select FileOpen Data File.
An Enter Data Filenames file selection dialog appears.
•
Select the file can_tmr.img from the list and click OPEN
The Available Bands List dialog will appear on your screen (Figure
2). This dialog lists all the available image bands in all open files.
The File button on the menu bar at the top of the dialog provides
access to file opening and closing, file information, and the Cancel
button. The Options button provides a function to find the band
closest to a specific wavelength, allows toggling between full and
shortened band names in the list, "folding" all of the bands in a single
open image into just the image name.
Figure 2: Available Bands List
CEE 6150 Remote Sensing Fundamentals
Lab #1: Introduction to ENVI
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Zoom box: shows the area
displayed in the zoom image
Zoom level
Subsample factor
Image box: shows the
area displayed in the
image window.
Figure 3: ENVI Main image display window with its own internal menus.
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Lab #1: Introduction to ENVI
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DOWNLOAD AND DISPLAY AN IMAGE FROM THE COURSE WEB SITE
• Open the course web page http://ceeserver.cee.cornell.edu/wdp2/cee6150/, and navigate to the Labs
page. There are two links listed under Lab 1 for a 1-band SPOT image.
• Left click on the spot_xi link save the file to your desktop. You may be able to just drag and drop the file.
(If that doesn't work, right click on the link and select "Save Link As", and save it to the desktop.) Also
save the header (spot_xi.hdr) to your desktop.
ENVI stores the image separately from the header data. The header file contains all the information necessary to
access the image: size, number of bands, center wavelengths, band widths, geographic location information, etc.
(This information is embedded in a single file in most standard image formats like jpg or gif.
Note: When downloading the files Windows may try to add a ".txt" extension to the header file.
This will render the file invisible to ENVI. If you cannot avoid saving the file without an
extra extension you will need to remove the extension by changing the file name in Windows
before ENVI will be able to find it.
• Within ENVI, select File  Open Image File, navigate to the SPOT image on the desktop and select the
image file (not the header file). The SPOT image should display as a color infrared image in which
vegetation appears red. The bands are shown in the Available Bands List window, and the displayed
band is shown below under Selected Bands.
• Redisplay the image as a black and white (B&W) image.
• In the Available Bands List window, click on the Gray Scale button.
• Select the band that you wish to display.
• Click on the button marked Display #1 and set the display to New Display.
• Display the ENVI Header by selecting
File  Edit ENVI Header in the main
ENVI menu. The information displayed
in this window is the minimum needed to
correctly import an image into ENVI. This
window will appear if there is insufficient
or no header information for the image
being imported.
• Click on Edit Attributes to see the list of
optional information that may be stored in
the header.
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Lab #1: Introduction to ENVI
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ENVI WINDOWS AND DISPLAYS
The group of three windows that display your image is collectively referred to as the "Display group". The
Display group consists of:
• The Main Display Window - this is where all or part of your image is displayed at full resolution.
• The Scroll Window - If your entire image does not fit in the Main window, the Scroll window will
appear. The Scroll window displays a reduced-size version of the entire image, which allows you to
select the portion that is displayed in the Main window. A colored box in the Scroll window indicates the
spatial location and coverage of the Full-Resolution Main Display window. A number in the title bar of
the Scroll Window tells you what reduction factor has been applied to the image to display the full spatial
extent within the Scroll Window.
• The Zoom Window - this window displays an enlarged version of a selected portion of the Main window.
A colored box in the Main Image Display indicates the spatial location and coverage of the Zoom
window. A number in the title bar of the Zoom Window tells you what zoom factor has been applied to
the image.
These three windows are intimately linked; changes to one window will be mirrored in the others. To get a feel
for how the display windows interact, try the following:
Drag the Zoom Indicator Box
• Note the small red box in the center of the Main window. This box indicates the area of the image
displayed in the Zoom window. You can drag the box from place to place in the Main window by
clicking inside the box with the left mouse button and dragging it to a new position. The Zoom window
is updated automatically to show the new area when you release the mouse button
• You can also reposition the zoom indicator box by placing the cross-hair cursor in the Main window and
clicking the left mouse button. The zoom region will be centered around the position you have chosen.
• Finally, if you click outside the zoom indicator box with the middle mouse button and hold and drag the
box to a new position, the Zoom window is updated as you move the box.
1. Zoom In and Out and Pan the Zoom Window
• Move the mouse cursor in the Zoom window and click the left mouse button to reposition the magnified
area by centering the zoomed area on the selected pixel.
• Clicking and holding the left mouse button in the Zoom Window while dragging causes the Zoom
Window to pan within the Main Image Display.
• Click the right mouse button in the Zoom Window to toggle the menu graphic on or off.
• Clicking the left mouse button on the "-" (minus) graphic zooms down by a factor of 1. Clicking the
middle mouse button on this graphic zooms down by a factor of 2. Clicking the right mouse button on the
graphic returns the zoom window to the default zoom factor.
• Clicking the left mouse button on the "+" (plus) graphic zooms up by a factor of 1. Clicking the middle
mouse button on this graphic zooms up by a factor of 2. Clicking the right mouse button on the graphic
returns the zoom window to the default zoom factor.
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• Click the left mouse button on the right (third) graphics box to toggle the Zoom Window crosshair
cursor. Click the middle mouse button on this graphic to toggle the Main Image crosshair cursor. Click
the right mouse button on this graphic to toggle the Zoom Box in the Main Image Window on or off.
Scroll the Image
• A red box in the Scroll window indicates what portion of the entire image is currently displayed in the
Main window. You can move the selected area by clicking inside the scroll indicator box with the left
mouse button and dragging the box to a new position. The displays in the Main and Zoom windows are
updated when you release the mouse button. You can also reposition the scroll indicator box by clicking
at the desired location using the left mouse button as for the Zoom window box above. If you click, hold
and drag the left mouse button in this fashion, the Image window will be updated as you drag (the speed
depends on your computer resources).
Resize the Windows
• You can resize the display windows the same way you would resize windows in other applications, by
dragging any of the corners. Note, however, that you cannot make the Main window larger than the
image size. If the Main window is large enough to display the entire image, the Scroll window is
unnecessary and is automatically removed from your screen. The Scroll window reappears if the Main
window is resized smaller than the full image.
Scroll Bars
• The Main Image Window can also have optional scroll bars, which provide an alternate method for
moving through the Scroll Image, allowing you to select which portion of the image appears in the Image
window. To add scroll bars, select FileWindow. Click on the arrow toggle next to the Scroll Bars
dialog in the Display Preferences window to toggle scroll bars on, then click OK at the bottom of the
dialog. The portion of the image displayed in the Image Window can now be controlled by clicking and
dragging the scroll bars using the left mouse button. Scroll bars can be turned on by default for all images
by selecting FilePreferences in the Main ENVI window. Next, select "Display Defaults" in the
System Preferences window and toggle the image window scroll bar switch.
ENVI FILE FORMATS
ENVI uses a generalized raster data format consisting of a simple "flat binary file" and a small associated ASCII
(text) header file. This file format permits ENVI to use nearly any image file, including those that contain their
own embedded header information. The separate text header file provides information to ENVI about the
dimensions of the image, any embedded header that may be present, the data format, and other pertinent
information.
ENVI is able to import a large range of image file types without requiring information from the user (Figure 4).
If you are able to identify the correct file format, ENVI will interpret the metadata for the given image type,
import the image and create an ENVI-style header.
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Lab #1: Introduction to ENVI
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Figure 4: External file formats directly accessible through ENVI.
You can view and edit the header data at a later time using the Edit ENVI Header function under the ENVI File
menu. You can also generate ENVI header files outside ENVI, using a text editor, if desired.
If ENVI cannot recognize a particular file format, you will need to specify the image characteristics in order for
the image to be imported correctly (Figure 5), these include information that should be readily available – the
number of samples per scan line, the number of lines in the scene, the number of bands in the image – and some
that may be unfamiliar:
Offset: The number of bytes of imbedded header information present in the file (for example, 128 bytes for
ERDAS 7.5 .lan files). ENVI Classic skips these bytes when reading the file.
x start and y start: Defines the image coordinates, also called "pixel coordinates." The default values are (1,1)
so that the upper-left hand pixel has an image coordinate of (1,1). This is needed if the image is a subset
of another image or has been registered to another image. If the image is to be used independently, then
the default value is sufficient.
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Lab #1: Introduction to ENVI
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Byte Order: The order of the bytes in
integer, long integer, 64-bit integer,
unsigned 64-bit integer, floating
point, double precision, and complex
data types. Use one of the following:
• Byte order=0 (Host (Intel) in the
Header Info dialog) is least significant
byte first (LSF) data (DEC and MSDOS systems).
• Byte order=1 (Network (IEEE) in the
Header Info dialog) is most significant
byte first (MSF) data (all other
platforms).
Data Type: The type of data representation,
where 1=8-bit byte; 2=16-bit signed
integer; 3=32-bit signed long integer;
4=32-bit floating point; 5=64-bit
double-precision
floating
point;
6=2x32-bit complex, real-imaginary
Figure 5: Data required to import am image into ENVI
pair of double precision; 9=2x64-bit
double-precision complex, real-imaginary pair of double precision; 12=16-bit unsigned integer; 13=32bit unsigned long integer; 14=64-bit signed long integer; and 15=64-bit unsigned long integer.
Interleave: Refers to whether data are in BSQ, BIP or BIL format. Generalized raster data is stored as a binary
stream of bytes in either Band Sequential (BSQ), Band Interleaved by Pixel (BIP), or Band Interleaved
by Line (BIL) format.
• BSQ is the simplest format, with each line of data followed immediately by the next line of the same
spectral band. BSQ format is optimal for spatial (X,Y) access to any part of a single spectral band.
• BIP format provides optimal spectral processing performance. Images stored in BIP format have the first
pixel for all bands in sequential order, followed by the second pixel for all bands, followed by the third
pixel for all bands, etc., interleaved up to the number of pixels. This format provides optimum
performance for spectral (Z) access of the image data.
• BIL format provides a compromise in performance between spatial and spectral processing and is the
recommended file format for most ENVI processing tasks. Images stored in format have the first line of
the first band followed by the first line of the second band, followed by the first line of the third band,
interleaved up to the number of bands. Subsequent lines for each band are interleaved in similar fashion.
A variety of data types is supported: byte, integer, unsigned integer, long integer, unsigned long integer,
floating-point, double-precision floating-point, complex, double-precision complex, 64-bit integer, and unsigned
64-bit integer.
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Lab #1: Introduction to ENVI
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USE THE MOUSE BUTTON DESCRIPTIONS
ENVI has many interactive functions, and the mouse button
combinations and actions are different for each one. The
Mouse Button Descriptions dialog is provided to tell you
what the mouse buttons do in each graphics window.
• To start the Mouse Button Descriptions select
WindowMouse Button Descriptions.
Now whenever your cursor is in an ENVI display or
Figure 6: Mouse Button Descriptions
graphics window, the mouse button assignments will be
listed in this dialog (Figure 6). MB1 is the left mouse button,
MB2 is the middle mouse button, and MB3 is the right mouse button.
DISPLAY THE CURSOR LOCATION
It is often important to know the exact location of the cursor within the image and the image value at that point.
• To display the cursor location and value, select
WindowCursor Location/Value from the ENVI
Main Menu.
A dialog box will appear displaying the location of the
cursor in the Main, Scroll, or Zoom windows (Figure 7).
The dialog also displays the screen value (color) and the
actual data value of the pixel underneath the cross-hair
cursor.
Figure 7: Cursor Location/Value window
• To dismiss the dialog, select "Cancel" from the pulldown File menu at the top of the dialog.
DISPLAY IMAGE PROFILES
X (horizontal), Y (vertical), and Z (spectral) profile plots can be selected and displayed interactively. These
profiles show the data values across an image line (X), column (Y), or spectral bands (Z).
1. ToolsProfilesX Profile to display a window plotting data values versus sample number for a
selected line in the image (Figure 8).
2. Repeat the process, selecting Y Profile to display a plot of data value versus line number, and selecting
Z Profile to display a spectral plot (Figure 6). Note: There are only six bands in the can_tmr.img, so the
spectral plot is rather simple.
3. Position the plot windows so you can see all three at once.
A red cross-hair extends to the top and bottom and to the sides of the Main window. The red lines indicate the
line or sample locations for the vertical or horizontal profiles.
4. Move the cross-hair around the image (just as you move the zoom indicator box), to see how the three
image profile plots are updated to display data on the new location. The Mouse Button Descriptions
dialog can be used to guide your exploration of these windows.
5. Close the profile plots by selecting FileCancel from within each plot window.
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Figure 8: Profile windows
Figure 9: Interactive Stretching window.
PERFORM INTERACTIVE CONTRAST STRETCHING
Interactive Contrast Stretching plots a histogram and allows you to interactively control the contrast of the
displayed image. Many different types of stretches can be applied. By default, a linear 2% stretch is applied to
the data when it is first displayed.
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• To access ENVI's interactive contrast stretching functions, select EnhanceInteractive Stretching from
the Main image display window.
A dialog that allows you to change the contrast stretch of the displayed image appears (Figure 7). Two
histogram plots display the color or grayscale range of the input image (left) and the output image after contrast
stretching (right). Initially, the input and output histograms reflect the default stretch applied to the data when
the image was displayed
• The Stretch_Type pulldown menu at the top of the histogram has a variety of contrast-stretching options.
Try applying the following methods described below and observe the results in the Main window.
• Also, try selecting both Zoom and Scroll from the Histogram_Source pulldown menu and note the
differences in the histograms and stretches.
Linear
When images are loaded into the Main window, a 2% linear contrast stretch is applied by default.
• Select EnhanceInteractive Contrast Stretching in the main display, then choose Linear from the
pulldown Stretch_Type menu item in the dialog
Note the dotted vertical lines in the input histogram plot--these bars can be repositioned to control the minimum
and maximum value used in the contrast stretch.
• Position the mouse cursor on the red bar and hold down the left mouse button, then drag the bar from
side to side.
Numbers above the plot display the current data value, the number of pixels and the percentage of pixels that
have that value, and the cumulative percentage of pixels with values less than or equal to the current value.
• Try positioning the left bar so that approximately 5% of the pixels are selected, and the right bar so that
approximately 95% of the pixels are selected.
• If OptionsAuto Apply On is selected, the stretch will be applied automatically. Otherwise, click
"Apply" to apply the stretch shown in the output histogram plot to the image in the Main window.
• You can also position the bars by entering minimum and maximum values in the fields next to the
"Apply" button at the top of the dialog. You can enter either data values or percentages.
• Enter "4%" in the left box and "96%" in the right box (press Enter after typing each value) and click
"Apply".
The left and right bars will be adjusted and the two text entries updated to display the data values at 4% and
96%, respectively.
Equalize
• Select Stretch_TypeEqualization and note the change in the "Output Histogram" display.
• If OptionsAuto Apply On is selected, the stretch will automatically be applied. Otherwise, click
"Apply" to apply the stretch shown in the output histogram plot to the image in the Main window.
Gaussian
• Select Stretch_TypeGaussian.
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• Set the Standard Deviation by selecting Options Set Gaussian Stdv.
• If OptionsAuto Apply On is selected, the stretch will automatically be applied. Otherwise, click
"Apply" to apply the stretch shown in the output histogram plot to the image in the Main window.
• Click "Cancel" to close the contrast stretching dialog.
DISPLAY INTERACTIVE SCATTER PLOTS
You can plot the data values of two selected image bands versus each other in a scatter plot to graphically
display the overlapping values.
1. Select Tools2D Scatter Plots in the Main image window.
A dialog will appear that lets you choose two image bands to compare.
2. Select one band for the X axis and another band for the Y axis and click "OK."
It may take a few seconds for ENVI to extract and tabulate the data values.
• Once the scatter plot has appeared
(Figure 10), position the mouse cursor
anywhere in the Main window and drag with
the left mouse button pressed.
• Pixel values contained in a ten-pixel by tenpixel box surrounding the crosshair will be
highlighted in red on the scatter plot. Again,
note that the Mouse Button Descriptions
dialog can help you know the functions of the
different mouse buttons in the Scatterplot.
• Move the cursor around in the Main window
to observe the "dancing pixels" effect.
• You can also use the scatter plot to highlight
specific data values in the Main window.
• Place the mouse cursor in the scatter plot
window and click and drag with the middle
Figure 10: An interactive scatterplot comparing Band 3 and
mouse button.
Band 4 values.
A ten-pixel-square box will appear in red on the plot. Pixels with the values contained in the box are highlighted
on the image in the Main window as "Image Dancing Pixels".
• Select File Cancel to close the scatter plot window.
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Lab #1: Introduction to ENVI
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DISPLAY A SPECTRAL PLOT
You can display a pixel in a spectral plot.
1. Select ToolsProfiles z-profile in the Main
image window.
In this case there are only 6 spectral bands, so the graph
is disjoined with straight lines connecting each point.
The red, green and blue lines mark the bands that are
used in the color image display.
2. Move the cursor to another location and left
click. The spectrum of that point will appear in
the spectral plot.
Figure 11: Spectral plot
3. In order to compare different spectra, select
OptionsCollect Spectra in the Spectral Profile window. Now each time you select a new point a
spectra will be added to the display in a contrasting color.
4. Based on the spectra, can you identify:
• Vegetation
• Forest
• Bare soil
• Snow
DISPLAY AND DISPLAY A SPECTRAL IMAGE
• Select File Open Image File. To bring up the Enter Data Filenames dialog.
• Navigate to the directory C:\Program Files\Exelis\ENVI50\Classic\Data
• Select the file cup95eff.int image from the list and click OK.
THIS IS A PORTION OF AN AVIRIS HYPERSPECTRAL IMAGE OF CUPRITE, NV.
In this case a set of 3 preferred bands has been identified for the image and a color image automatically displays
in a new image window. Try displaying the spectral plot for this image. Since there are 50 SWIR bands in this
image, the spectrum appears to be nearly continuous and is capable of showing much more spectral detail.
Explore the different areas and compare the spectral variability of the different areas in the image.
1. Display the spectral plot for this image. In the image window select ToolsProfiles z-profile. Since
there are many more spectral bands in this image, the spectrum shows much more detail.
2. There are a number of distinctly colored areas in the image. Examine the spectra by moving the cursor
to each in turn.
3. Compare the spectra from the different region, select OptionsCollect Spectra in the Spectral Profile
window. Now each time you select a new point a spectra will be added to the display in a contrasting
color.
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Lab #1: Introduction to ENVI
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DISPLAY A PAIR OF IMAGES AND LINK THE DISPLAYS
1. Display A Color Image
2. Click on the "Display #" button at the bottom of the Available Bands List and select "New Display" to
create a second display group.
3. Click on the "RGB Color" radio button and select and select three bands from the band list (at the top of
the window), and then click "Load Band" to load the image into the second display.
4. Link the Two Displays
When you link two displays, any action you perform on one display (scrolling, zooming, etc.) is echoed in the
linked display. To link the two displays you have on screen now:
5. Select Tools LinkLink Displays from one of the display windows.
6. Click "OK" in the Link Displays dialog.
7. Now try scrolling or zooming in one display group and observe as your changes are mirrored in the
second display.
8. Dynamic Overlays
ENVI's Multiple Dynamic Overlay feature allows you to dynamically superimpose parts of one or more linked
images onto the other image. Dynamic overlays are turned on automatically when you link two displays.
• To use the overlay, position the mouse cursor anywhere in either image window and click the left mouse
button. The linked image will appear in the active window.
• To adjust the transparency of the overlay image, right click in the image window, select "Adjust
Transparency” from the pull down menu, and adjust the transparency in the popup window.
• To change the size of the overlay area, hold down the middle mouse button and drag the overlay area
until it is the desired size. A small portion of the linked image will be superimposed on the current image
window. The overlay will appear in either the Main window or the Zoom window.
When done with this section, either close one of the image windows or turn off the image link option.
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Lab #1: Introduction to ENVI
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SELECT REGIONS OF INTEREST
ENVI lets you define "Regions of Interest" (ROIs) in your
images. ROIs are typically used to extract statistics for
classification, masking, and other operations.
1. Select Basic ToolsRegion of Interest Define
Region of Interest from the ENVI Main Menu. The
ROI Definition dialog will appear (Figure 10).
2. Draw a polygon that represents the region of interest.
Click the left mouse button in the Main window to establish
the first point of the ROI polygon.
Figure 12 Region of Interest (ROI) Tool window
Select further border points in sequence by clicking the left button again, and close the polygon by clicking the
right mouse button.The middle mouse button deletes the most recent point, or (if you have closed the polygon)
the entire polygon.
• ROIs can also be defined in the Zoom and Scroll windows.
When you have finished defining an ROI, it is shown in the dialog's list of Available Regions, with the name,
region color, and number of pixels enclosed (Figure 10).
1. To define a new ROI, click "New Region".
2. You can enter a name for the region and select the color and fill patterns for the region by clicking on
the "Edit" button.
Other types of ROIs
ROIs can also be defined as polylines or as a collection of individual pixels by selecting the desired ROI type
from the ROI_Type pulldown menu. See the ENVI User's Guide or the hypertext online help for further
discussion of these types of ROI.
Working with ROIs
You can define as many ROIs as you wish in any image.
• Once you have created the ROI definitions, you can erase them from the display (leaving the definition in
the list) by selecting the ROI from the list and clicking on the "Erase" button.
• Clicking on the "Stats" button allows you to view statistics about the ROI you select.
• Clicking the "Delete" button permanently deletes ROI definitions from the list.
• The other buttons and options under the pulldown menus at the top of the ROI Definitions dialog let you
calculate ROI means, save your ROI definitions, load saved definitions, or display or delete all the
definitions in the list.
Region Of Interest definitions are retained in memory after the ROI Definition dialog is closed, unless you
explicitly delete them. This means the ROIs are available to other ENVI functions even if they are not displayed.
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ANNOTATE THE IMAGE
ENVI's flexible annotation features allow you to add text, polygons,
color bars, and other symbols to your plots and images.
• To annotate an image, click the right mouse button in the Main
Image window and select FunctionsOverlays Annotation.
The Annotation dialog will appear (Figure 11).
• To annotate plots, 3-D surfaces, and similar objects, select
OptionsAnnotation within the plot windows.
Annotation Types
The Annotation dialog allows you to choose from a variety of
annotation types. Different types are selected from the Object menu and
include Text, Symbols, Rectangles, Ellipses, Polygons, Polylines,
Figure 13: Annotation
Arrows, Map Scale Bars and Declination Diagrams, Map Keys, Color
Table Ramps, and Images. By default, the Annotation dialog starts up
with "Text" selected. Other fields in the dialog let you control the size, color, placement, and angle of the
annotation text. When you select different annotation types from the menu, the fields in the dialog change to
display options appropriate to the new type.
Placing Annotation
Try placing a text annotation in your Main window:
1. Type some text in the text field in the center of the dialog.
2. Select a font, color, and size from the appropriate menus and parameters in the dialog, then position the
mouse pointer in the Main window and press the left mouse button. Again, the Mouse Button
Description dialog will help you remember the mouse button interactions within annotation.
Your text will be displayed in the window at the point you chose.
3. Drag the handle using the left mouse button to position the text.
4. You can continue to change the annotation's properties and position by changing the fields in the dialog
box or dragging the text or symbol while holding down the left mouse button.
5. When you are satisfied with the annotation, press the right mouse button to fix the annotation in
position.
Saving and Restoring Annotation
• You can save your image annotation by selecting FileSave Annotation in the Annotation dialog.
• If you do not save your annotation in a file, it will be lost when you close the Annotation dialog (you will
be prompted to save the annotation if you close without first saving).
• You can also restore saved annotation files by selecting FileRestore Annotation in the dialog.
Editing Previously Placed Annotation
To edit an annotation element that has already been "fixed" on the image:
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1. Select ObjectSelection/Edit in the Annotation dialog.
2. Draw a box around the annotation you wish to edit by clicking and dragging with the left mouse button.
3. When the handle reappears, move and configure the item just as you would a new annotation.
Suspending the Annotation Function Temporarily
• To suspend annotation operations and return to normal ENVI functionality temporarily, select the "Off"
toggle button at the top of the Annotation dialog.
This allows you to use the scroll and zoom features in your display without losing your annotations.
• To return to the annotation function, select the toggle button for the window you are annotating.
Leave your annotation on the Main window image as you complete this tutorial.
ADD GRID LINES
Try adding a grid to your image:
4. To overlay grid lines on your image, select OverlayGrid Lines in the Main display window.
5. You can adjust the grid lines by setting the line thickness and color and the grid spacing using the
Options pulldown menu.
An image border is automatically added when you overlay grid lines.
•
When you have added a satisfactory grid, click "Apply" in the Grid Line Parameters dialog.
SAVE AND OUTPUT AN IMAGE
ENVI gives you several options for saving and outputting your filtered, annotated, gridded images. You can
save your work in ENVI’s image file format, or in several popular graphics formats (including Postscript) for
printing or importing into other software packages. You can also output directly to a printer.
Saving your Image in ENVI Image Format
To save your work in ENVI's native format (as an RGB file):
• Select FileSave Image AsImage File in the Main Image window.
The Output Display to Image File parameter dialog will appear.
• Select 24-Bit color or 8-Bit grayscale output, graphics options (including annotation and gridlines), and
borders.
If you have left your annotated and gridded color image on the display, both the annotation and grid lines will be
automatically listed in the graphics options.
You can also select other annotation files to be "burned in" to the output image.
1. Select output to "Memory" or "File".
2. If output to "File" is selected, enter an output filename.
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3. Click "OK" to save the image.
4. If you select other graphics file formats from the "Output File Type" button, your choices will be
slightly different.
END THE ENVI SESSION
• When you have finished your ENVI session, click "Quit" or "Exit" on the ENVI Main Menu.
DOWNLOAD DATA FROM A USGS SERVER
Much of the U.S., Canadian and European government and commercial satellite imagery is available
for direct download via the internet. A substantial amount of this data is free. There are many sites
from which data can be accessed, but we'll try only one site.
1. In a web browser, navigate to http://glovis.usgs.gov/. The site provides a graphical interface to select
imagery, allowing the user to select:
• The imaging system (default is Landsat)
• The geographic location
• The time frame
2. To begin, click on a point of interest on the global map. A new window appears showing a mosaic of
the most recent cloud-free browse images around the point you selected. From here, you can begin to
explore the other images from the archive:
• Roam around on the earth's surface by clicking on either the arrow buttons or the global locator map
near the top left of the display. You can also "shortcut" to a specific location by entering the desired
WRS-2 (WRS-1 for Landsat 1-3 data) "path" and "row" or latitude and longitude.
• Limit the range of scenes to view by setting search limits in the search limits dialog box. The search
limits dialog box is opened by selecting the "Tools" menu from the menu bar and then clicking on
"Search Limits...".
• View the available images for the highlighted scene with the "Prev Scene" and "Next Scene" buttons.
You can also "shortcut" to a specific date by entering the month and year. The possible dates will be
dependent upon the sensor, as well as the specific data in the USGS browse image inventory.
• Scenes with high cloud cover can be excluded by adjusting the maximum cloud cover setting (via the
"Max Cloud" drop-down menu).
• To help determine where you are, select the "Map Layers" menu on the menu bar. You will then be
able to view admin boundaries, country boundaries, the collection grid, roads, water, north arrow,
and/or World Cities (and others).
• Limited "zoom in" and "zoom out" can be achieved by selecting the "Resolution" menu on the menu
bar and clicking on the resolution to be viewed.
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3. When you locate an image of interest, add it to your request list (bottom left button). Once you have
selected a set of images you can download submit the order.
4. When your scene list is complete, click on the "Order" button (where available) or "Submit" button
(where available) in the scene list dialog box or right-click on the scene list dialog box for a popup
menu and select "Order" or "Submit".
Note 1: You will have to register (free) and fill out identification and address information in order to
submit an order.
Note 2: If you have scenes from different datasets, you will need to do this separately for each
dataset).