GISC 7365: Remote Sensing Digital Image Processing

Instructor: Dr. Fang Qiu

Lab Four: Density Slice and Image Composition

Objective:

Through this lab, students will learn

·  How to measure distance and area on an image

·  How to density slice an image to gain understanding

·  How to make image maps in IMAGINE

Part I: Basic Map Measurements.

The measurement tools are a quick means of getting positional and areal values for specific targets on the image.

·  Open the SPOT XS image of Marco Island, FL (i.e., mi-fl_10-21-88spot.img). Open Raster Layer (Folder Icon). Select mi-FL_10-21-88spot.img. Click on the Raster Options tab. Display as: True Color, Layers To Colors: Red-3; Green-4; Blue-2, check Clear Display, check Fit to Frame. Then click on OK. You are now looking at a false-color composite of XS Bands 3, 4, 2 (R, G, B).

·  Click the Measure button from the Information tab group under the Home tab. The Measurement Tool dialog is displayed.

·  In the Measurement Tool dialog, set the unit of linear measure to Meters and area measurement to sq. Miles.

·  Practice with the tools and get comfortable with how they work. The location tool only needs to be clicked once; the distance tool needs a double click to stop the line segment; and the area tool also needs a double click to close the polygon.

Homework: Use the Measurement Tools to answer the following:

Q1: Give the approximate center location of the sand bar at the center of the image (in Latitude and Longitude).

Q2: What is the perimeter (in meters) and area of the sand bar (in square miles)?

·  When finished, in Measurement Tool dialog, click File and then select Close to close the Measurement Tools dialog. Do not save changes.

Part II: Density Slice

Raw TM Data Band 3 / 5 Class Density Slice

Density slicing is a form of selective one-dimensional classification. The continuous gray scale of an image is "sliced" into a series of classes based on ranges of brightness values. All pixels within a "slice" are considered to be same information class (i.e. water, forest, urban etc.). This slicing takes place in the Attribute Table of the image.

·  Copy mi-fl_10-21-88spot.img into your working directory. Look at the file property and uncheck Read-only attribute. Open the image file as a Pseudo Color image using the NIR layer (band 3). Then select “nir_band” in the Band dropdown menu from the View tab group under the Thematic tab. You are going to density-slice the image into three general land cover classes:

o  Water

o  Vegetation

o  Urban/Barren

·  To do this you will need to select the Show Attributes button from the View tab group under the Table tab. Also, bring up the raw data value histogram for band 3 to aid in your feature discrimination using Image Metadata window.

·  Once you have both a histogram and an Attribute Table open you are ready to proceed. Examine the rows and columns in the Attribute Table. The rows in the menu correspond to the input file data values that can range from 0 to 255 (8 bits). The columns show, among other things, the color that is currently assigned to each of the brightness values available in the image. As you scroll through the Raster Attribute Editor you should see a progression from dark to light in color.

·  Move the cursor back into the 2D View where the NIR band is displayed and with the right mouse button select Inquire. Roam the cursor around the image and watch to see what typical brightness values (Pixel Values) are associated with the water class, the vegetation class, and the urban/bare land class in the NIR band. You should be trying to get an idea about what boundary values correspond with each of these classes (i.e. vegetation = 40 to 56, water = 6 to 9, urban/bare land 70 to 107, NOTE: these are wrong choices and are only used for example). At this point you may wish to consult the histogram of the NIR band to make any further "guesstimates" as to the class into which you plan to place a particular brightness value.

·  After you have used the inquire cursor and determined the boundary values for the three classes move back to the Attribute Table. What you will now do is to assign to each of these three classes characteristic colors that will represent them in the image (i.e. instead of water being dark black in the NIR band it will appear as the color you chose- blue might be nice). The method for assigning your range a characteristic color is quite simple. Use the left mouse button to "highlight" each row you feel is characteristic of one particular class, i.e. water. This can be done by clicking on each row number (farthest left column) individually, or by selecting a series of rows by depressing the left mouse button and keeping it depressed, moving the mouse up or down within the row column. This will have the effect of scrolling the attribute editor up or down, highlighting all the rows along the way. If you wish to do a combination of scrolling and selecting individually then make sure you hold the shift key down anytime you depress the left mouse button and proceed as before.

·  Once you have made your row selections you can modify the color in all of them by depressing the right mouse button when the cursor is over the color column (Note that the color will only change in the rows you have selected and similarly you can only change the color in rows you have selected).

Homework:

Q3: Record the range of values you used to density slice each land cover class:

o  Water =

o  Vegetation =

o  Urban/Bare land =

·  Close the Attribute Table and Save the changes.

Note: In grading the color coded NIR band I will be looking for: Are the 3 land cover classes ask for represented correctly (i.e. are the boundary choices within reason for the classes ask for)? Were there 3 different colors assigned to the 3 different classes? Do the colors reasonably represent their land cover classes (i.e. red for water would be a poor choice etc.)?

Part III. Map Composition

The ERDAS Imagine Map Composer is a WYSIWYG (What You See Is What You Get) editor for creating cartographic-quality maps and presentation graphics. Maps can include single or multiple continuous raster layers, thematic (GIS) layers, vector layers, and annotation layers. In this lab, we are going to create an image map of your density slice image results.

Step 1. Start Map Composition:

·  To start the map composition process, select File – New – Map View.

·  When the New Map View opens, select File – Save As – Map Composition As. Input lab4.map as the new map name, and save it to your working directory.

·  Click the Page Size button from the Page tab group under the Layout tab. Specify a Map Width of 7.5 and a Map Height of 10 (to allow for a small margin on the 8.5 x 11 map).

·  Make sure the unit is set to inches and then click OK.

·  With your cursor in the Map View, right click mouse and select Fit to Frame, so that you can see the entire map composition page.

·  In the 2D View, open your density slice file and select Fit to Frame before opening.

·  Once this image is opened, you must now define your map frame (where you want your image to appear on your composition).

Step 2. Draw the Map Frame.

·  Click the Map Frame button from the Insert Map Element tab group under the Layout tab to draw the boundary of the map frame in the Map View. Make sure you allow ample space on all sides for the title, legend, north arrow, and scale bar and tic marks.

·  When you release the mouse button, the Map Frame Data Source dialog should appear. Click on Viewer... and then left click anywhere in the 2D View displaying the density slice image. In the Map Frame dialog, Click on Use Entire Source and click OK.

·  In the Contents window, click on the name of the density slice image under the map frame item. Select “nir_band” in the Band dropdown menu from the View tab group under the Thematic tab. Now the images displayed in the map frame and in the 2D View should be the same.

·  You may select the map frame by clicking on it. You can select any map frame within the composition for resizing or repositioning purposes.

·  If you make a mistake during this long process, you can delete a map frame by selecting it and pressing Del key on your keyboard.

Step 3. Add a Neatline and Tick Marks.

Next we will add a neatline and some tick marks to our composition. A neatline is a rectangular border around a map frame. Tick marks are small lines along the edge of the map frame that indicate the map units (meters, feet, etc.). You must be using a georeferenced image in order to produce tick marks.

·  Now click the Map Grid button from the Insert Map Element tab group under the Layout tab. Click on the map frame on which you want to place the neatline and tick marks.

·  When the Set Grid/Tick Info dialog appears enter the following parameters:

Horizontal Axis (Length Inside) = 0.06

Horizontal Axis (Length Intersection) = 0.06
Spacing = 500
Click on Copy to Vertical (to copy to vertical axis)
Click Apply

·  If you are satisfied with the appearance of the neatline, click Close in the Set Grid/Tick Info dialog, otherwise modify the parameters and click Redo (not Apply). You can also click Undo button on the Quick Access Toolbar to make adjustments.

Step 4. Add Annotations to different kinds of land cover types.

·  Click on the Text button from the Insert Geometry tab group under the Drawing tab.

·  Move your cursor in the Map View where you want to place text. Single click and enter a text string.

·  Select the text by single-clicking it. You can edit the text by single-clicking it after you select it. A double click with the mouse will bring up the Text Properties window. You can move the text by selecting it (lmb) and sliding it around while holding the lmb down. A box will appear around the text string and you can also alter the size by selecting the box and manipulating it...experiment.

·  If you want to make any changes in font style, color etc., select the text and make such changes in the Font tab group and Style tab group under the Format tab.

·  You can rotate the annotation text after you select it by pressing the green dot on top of the text box and dragging your mouse.

Step 5. Make a Scale Bar.

·  Click the Scale Bar button from the Insert Map Element tab group under the Layout tab. Move the cursor into the Map View and the cursor changes to the scale bar positioning cursor.

·  Drag the mouse to draw a box under the right corner of the map frame, outlining the length and location of the scale bar. You can change the size and location later if needed. Follow the directions by clicking in the map frame to indicate that this is the image whose scale you are showing.

·  In the Scale Bar Properties dialog, select Feet as the Units and set the Maximum Length to 2.0 Inches. Click Apply. You may reposition the scale bar by clicking it and dragging it to the desired position.

Step 6. Add a Map Title.

·  Click on the Text button from the Insert Geometry tab group under the Drawing tab. Move the cursor to the top of the map and click where you want to place text.

·  Enter the following title: “Density Slice Map.” Select the title text and change the text font according to the following parameters in the Font tab group under the Format tab.

Size: 30 points
Font Name: Antique-Olive (Under the Custom tab)

·  Position the title by double-clicking on the text and entering the following parameters in the Text Properties dialog:

X: 4.0
Y: 9.5
Vertical Alignment: Center
Horizontal Alignment: Center

·  You can also manually do the resizing and alignment.

·  Click Apply and then close the dialog.

Step 7. Place a North Arrow.

Map Composer contains many symbols, including north arrows. These symbols are pre-drawn groups of elements that are stored in a library.

·  Click the North Arrow button from the Insert Map Element tab group under the Layout tab. Move the cursor into the Map View and Drag the mouse to draw a box where you want to place it, outlining the length and location of the scale bar. You can change the size and location later if needed.

·  In the Style tab group under the Drawing tab, select north arrow 2 from the North Arrows category. In the Font/Size tab group under the same tab, change the size to 36 points.

·  You can reposition the scale bar and north arrow so they appear neat and orderly on the composition. Remember you can double-click on most graphics to bring up a Properties dialog for editing purposes.

Step 8. Write Descriptive Text.

Below the image, include on your map composition the following descriptive text using the following properties:

By Your Name

Program in Geographic Information Sciences

University of Texas at Dallas

October, 2006

Size: 10 points
Text Font: Antique-Olive
Fill Style: Solid Black

Step 9. Print the Map Composition.

Save the map composition by selecting File – Save or clicking the Save button on the Quick Access Toolbar. Reopen it in EDRAS IMAGINE. Print screen of your generated map.