ENVI Tutorial #7

Map Composition Using ENVI

The following topics are covered in this tutorial:

Overview of This Tutorial

Files Used in this Tutorial

Background - Map Composition in ENVI

Getting Started

Image Display and Map Layout

Overview of This Tutorial

This tutorial is designed to give you a working knowledge of ENVI's map composition capabilities. For additional information please see the ENVI User's Guide or the ENVI On-Line Help.

Files Used in this Tutorial

You must have the ENVI TUTORIALS & DATA CD-ROM mounted on your system to access the files used by this tutorial, or copy the files to your disk.

The files used in this tutorial are contained in the YS_TMSUB subdirectory of the ENVIDATA directory on the ENVI TUTORIALS & DATA CD-ROM.

Required Files

The files listed below are required to run this exercise. 

YSRATIO.IMG	Yellowstone National Park TM Ratio Subset Image
YSRATIO.HDR	ENVI Header for Above
YSRATIO.ANN	Saved Annotation Result for Above
YSRATIO.GRD	Saved Grid Parameters for Above
YS_LOC.GIF	Location Image for Above

Background - Map Composition in ENVI

Map composition requires that the user be able to easily and quickly go from an image to an image-based map by interactively inserting the key map components. Map composition consists of defining the map extent; positioning the image within the extent using borders; adding pixel, map coordinate, and/or geographic (latitude/longitude) coordinate grids; constructing map keys, declination diagrams, and map scales; as well as placement of inset images and annotation.

Getting Started

Composing a map in ENVI is as simple as displaying the image, and then interactively adding the individual map components such as annotation, map scales, gridlines, etc. Templates of common map objects can be built and saved, and much of the placement of the objects used for map composition can be automated through the use of templates.

To begin, select the image for map composition, open the file, and load as a grayscale or RGB image into one of ENVI's display windows with the desired contrast stretch as indicated below.

Start ENVI

Before attempting to start the program, ensure that ENVI is properly installed as described in the installation guide.

The ENVI Main Menu appears when the program has successfully loaded and executed.

Open and Display Landsat TM Data

To open an image file:

  1. Select File ->Open Image File on the ENVI Main Menu.

Note that on some platforms you must hold the left mouse button down to display the submenus from the Main Menu.

An Enter Input Data File file selection dialog appears.

  1. Navigate to the YS_TMSUB subdirectory of the ENVIDATA directory on the ENVI TUTORIALS & DATA CD-ROM just as you would in any other application and select the file YSRATIO.IMG from the list and click "OK".

The Available Bands List dialog will appear on your screen. This list allows you to select spectral bands for display and processing.

Note that you have the choice of loading either a grayscale or an RGB color image.

  1. Select the first three bands listed at the top of the dialog by first selecting the RGB Color radio button in the Available Bands List, then clicking on the bands sequentially with the left mouse button.

The bands you have chosen are displayed in the appropriate fields in the center of the dialog.

Click "Load RGB" to load the image into a new display.

Once the image is displayed, follow the steps below for individual components and the sequence of map composition.

Figure 1: Yellowstone National Park Landsat TM Color Ratio Composite image. Ratios 5/7, 3/1, and 3/4 as RGB.

Image Display and Map Layout

The ENVI Main Display window, Scroll window, and/or Zoom window are used to perform map composition. If working in the Scroll Window, you may want to enlarge it by dragging one of the corners to resize the display.

Figure 2: ENVI Map Composition Layout Screen in the Scroll Window.

 

Virtual Borders

Default ENVI displays contain only the image, with no surrounding blank space. Map composition typically requires that some map objects reside outside the image proper. ENVI provides a "Virtual Border" capability that allows annotation in the image borders without creating a new image. Virtual borders can be added to an image in several ways.

Automatically Added When Using Image Grids

  1. Toggle on the Functions menu in the Main Display window by clicking the right mouse button in the display and select Functions->Overlays->Grid Lines.

A virtual border will be added to accommodate the grid. See the specific grid instructions below for information on setting up the grid. A 100-pixel border is automatically added on all sides of the image.

  1. If you want to change from the default border, when the Grid Line Parameters dialog appears, choose Options->Set Display Borders to start the Display Borders dialog.
  2. Enter the desired border characteristics and click "OK".

 

The new virtual border characteristics will be applied immediately to the image. If you save the Grid Parameter File, the border information will be saved with the grid and will be restored when the grid parameters file is restored.

Using the Available Bands List:

  1. Select Options->Set Display Borders in the menu bar in the Available Bands List.

The Set Display Borders dialog will appear with the number of border pixels listed in text boxes that correspond to image geometry. This dialog is also used in Grids and Annotation to set the virtual border size.

  1. Enter the desired values in the appropriate text boxes.

The top text box controls the top border, the right text box the right border, the bottom text box the bottom border, and the left text box the left border.

  1. To set the border color, select from the list using the "Border Color" button.
  2. Click "OK" to set the border.

The next image displayed using the Available Bands List will be displayed with the borders applied.

Using the Display Characteristics Function:

  1. Toggle on the Functions menu in the Main Display window by clicking the right mouse button in the display and select Functions->Display Characteristics->Change Display Parameters.

The Display Parameters dialog will appear, containing text boxes similar to those described above.

  1. Enter the desired values and select the desired color for the border.
  2. Click "OK".

The new borders will be applied to the image immediately.

Using the Annotation Function:

  1. Toggle on the Functions menu in the Main Display window by clicking the right mouse button in the display and select Functions->Overlays-> Annotation.
  2. When the Annotation dialog appears, select Options->Set Display Borders to start the Display Borders dialog.
  3. Enter the desired border characteristics and click "OK".

The new virtual border characteristics will be applied immediately to the image. If you save the Annotation File, the border information will be saved with the annotation and will be restored when the annotation file is restored.

 

Image Grids

ENVI supports simultaneous pixel, map coordinate, and geographic (latitude/longitude) grids. A 100-pixel virtual border (which can be adjusted as described above) is automatically appended to the image to accommodate the grid labels when Grids are applied. To add grids to an image:

  1. Toggle on the Functions menu in the Main Display Window by clicking the right mouse button in the display and select Functions->Overlays->Grid Lines in the Main Display window.

The Grid Line Parameters dialog will appear with default grid spacings set.

  1. Click "Apply" to display the grids with the default grid spacings or choose Options->Edit Pixel Grid Attributes or Edit Map Grid Attributes or Edit Geographic Grid Attributes to edit the attributes of the selected grid.

This allows editing of the line and label characteristics for the grid.

  1. Click "OK" to apply the selected attributes.
  2. Click "Apply" in the Grid Line Parameters dialog to post the new grid to the displayed image.

To save Grid parameters for later use, select File->Save Setup from the Grid Parameters menu bar and select an output file.

This saves a template of the grid parameters, which can be recalled for use on another map composition by choosing File ->Restore Setup from the Grid Parameters menu bar.

Annotation

Annotation is used as a generalized means of inserting map objects into an ENVI display for map composition. Several classes of map objects are available and all are placed using ENVI's standardized annotation procedures.

  1. Toggle on the Functions menu in the Main Display window by clicking the right mouse button in the display and select Functions->Overlays-> Annotation to start the Annotation dialog.
  2. Choose the desired annotation object from the Object pulldown menu in the Annotation dialog menu bar.
  3. Place the object by dragging using the left mouse button and clicking the right mouse button to lock the annotation in position.
  4. All annotation objects can be reselected, modified, and moved by choosing Object->Selection/Edit followed by selecting the object by drawing a box around it using the left mouse button.
  5. Clicking the right mouse button re-locks the annotation.

 

The various types of annotation available in ENVI are discussed below. Please see the ENVI User's Guide or the ENVI On-Line Help for more details.

Text and Symbols

ENVI currently has 14 standard text fonts and 3 different standard symbol sets. In addition, ENVI can utilize TrueType fonts installed on your system. This provides access to a wide range of different text fonts and symbols. All of these can be interactively scaled and rotated, and different colors and thickness can be set.

Figure 6: ENVI Text Annotation

  1. Select Object ->Text or Object ->Symbol from the Annotation menu bar.
  2. For text annotation, select the font from the pulldown font button in the left center of the dialog. Select size, color, and orientation parameters using the appropriate buttons and text entry boxes in the center of the dialog.

TrueType fonts provides more flexibility. Select one of the available Truetype fonts available on your system by choosing TrueType from the pulldown Font menu and selecting the desired font. Enter the character you want and place using the methods described above.

  1. For symbols, select the desired symbol from the table of symbols that appears in the Annotation dialog when this object is selected.
  2. Place the text or symbol on the image as described above, position with the left mouse button, and place by clicking the right mouse button.
  3. Reselect, modify, and move the annotation as desired.

Polygons and Shapes

ENVI allows you to draw rectangles, squares, ellipses, circles, and free-form polygons. These can be an outline only, or filled with a solid color or a pattern. Placement is interactive, with easy rotation and scaling.

  1. Select Object->Rectangle, Object->Ellipse, or Object->Polygon in the Annotation dialog.
  2. Drag and place the shapes as described above.
  3. For polygons, use the left mouse button to define polygon vertices and the right mouse button to close the polygon.

Lines and Arrows

ENVI annotation allows the placement of polylines (lines) and arrows. You have full control over the color, thickness and linetype, and the fill and head characteristics for arrows.

  1. Select Object->Polyline or Object->Arrow in the Annotation dialog.
  2. Define arrows and lines by clicking with the left mouse button.
  3. Click using the right mouse button to close the current line.

Map Scales

Map Scales are automatically generated by ENVI based on the pixel size of the image being used in the map composition. Options include feet, miles, meters, and kilometers. Scales can be placed individually, or in groups. The number of divisions and minor divisions is completely configurable, as is the font and the character size.

  1. Select Object->Scale Bar in the Annotation dialog.
  2. Enter the desired parameters, then place the scale bar using the left mouse button.
  3. Lock in the annotation using the right mouse button.

Declination

ENVI automatically generates declination diagrams based on user-provided characteristics. The size of the diagram and the azimuths for True North, Grid North, and Magnetic North are entered in decimal degrees and the diagram is placed using standard ENVI annotation procedure.

  1. Select Object->Declination in the Annotation dialog.
  2. Place the annotation using the left mouse button.
  3. Lock in the annotation using the right mouse button.

Map Keys

Shown below is an example of a map key build using ENVI's map key editing facility. The box around the key is a rectangle placed as a separate annotation object as is the key description at the top of the box.

  1. Select Object ->Map Key in the Annotation dialog.
  2. Choose Edit Map Key Items to add, delete, or modify individual map key items.
  3. Place the map key using the left mouse button and lock in using the right mouse button.

Map keys are generated automatically for classification images and vector layers.

Color Ramps

You can create grayscale ramps and color bars for grayscale and color-coded images respectively. This option is not available when an RGB image is displayed.

  1. Select Object->Color Ramp in the Annotation dialog.
  2. Enter minimum and maximum values and intervals as desired and set vertical or horizontal orientation.
  3. Place the color ramp using the left mouse button.
  4. Lock in the annotation using the right mouse button.

Image Insets

While many images are inset into other image using ENVI's mosaicking capabilities, ENVI annotation provides the capability to inset images into other images during the map composition/annotation process as well.

  1. Select Annotation->Object->Image.
  2. Click "Select New Image" to choose the image to be inserted (the image must previously be opened and listed in the Available Bands List).
  3. Pick the image from the Available Bands List, perform any spatial subsetting, and resize on-the-fly if desired.
  4. Place the image using the left mouse button.
  5. Lock the image in using the right mouse button.

Because 8-bit displays can not easily assign a new color table to the inset image, ENVI only shows a representation of the image in the display window. The actual image is placed when the image is output to a file and the annotation is burnt in.

Plot Insets

ENVI annotation also provides the capability to inset ENVI plots into other images during the map composition/annotation process. These vector plots will maintain their vector-ness (not rasterized) on output to PRINTER or POSTSCRIPT (note: they will not show up on output to image.)

  1. Select Annotation->Object->Plot.
  2. Click "Select New Image" to choose the plotto be inserted (the plot must be displayed on-screen). Types of plots supported include X-, Y-, spectral-, and arbitrary profiles, and spectral plots.
  3. Pick the plotfrom the Select Plot Window dialog, set the size of the plot by entering the desired dimensions, and click OK.
  4. Place the plot using the left mouse button.
  5. Lock the plot annotation into the image using the right mouse button.

Because 8-bit displays can not easily assign a new color table to the inset plot, ENVI only shows a representation of the plot in the display window. The actual plot is placed when the image is output directly to the printer or a postscript file and the annotation is burnt in. Again, this option does not produce a vector plot in output to image.

Vector Layers

ENVI can import ArcShape, Arc/Info Interchange, DXF, and DLG vector formats. Vectors from these files and internal ENVI Vector Files (.evf) can be used in an ENVI map composition.

  1. Open the files by selecting File->Open Vector File->the appropriate file type.
  2. Load the vectors into the map composition display, by clicking on Apply and adjust the attributes to obtain the desired colors, thickness, and linetypes. See the Vector Overlay and GIS Analysis Tutorial in this volume or see the ENVI User's Guide or on-line help for additional information.

Output

The image-map composition can be output from the Main Display window.

  1. Set the annotation to "Off" in the Annotation dialog.
  2. Click the right mouse button in the Main Display window and select Functions->Output Display->the desired output type.

Options include Postscript, ENVI (binary) image, BMP, GIF, HDF, JPEG, PICT, SRF, TIFF, and XWD, as well as common image processing system formats such as PCI, ERDAS, ERMAPPER, and ArcView Raster.

You can also select direct printing, in which case, the map composition will be printed directly to your hardware using system software drivers.

In all of the above cases, graphics and map composition objects will be burned into the image on output.

The figure below shows an example of a finsl map composition produced in ENVI.

Copyright © 1993 - 1999, BSCLLC, All rights reserved. ENVI is a registered trademark of Better Solutions Consulting LLC, Lafayette, Colorado,Web: http://www.envi-sw.com, Email: envi@bscllc.com. .(Last Update, April 26, 1999)