Open and Display Images

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Lesson content

Lesson 1 of 1

Open and Display Images

In this quick guide, you will:

•

Open and display an aerial orthophoto in ENVI. * •

Use navigation tools to explore the orthophoto. * •

Work with placemarks. * •

View pixel values and geographic coordinates in the Status bar. * •

Display the Overview Window.

Sample Data

Download sample data below. Then extract the contents of the .zip file to a local directory.

[GettingStarted.zip

116 MB

DownloadArrow down with horizontal line beneath it](assets/GettingStarted.zip)

1

Select File > Open from the Menu bar. An Open dialog appears. 2. 2

Go to the location where you saved the sample data. Select CentralParkOrthophoto.dat and click Open. 3. 3

Press the F12 key on your keyboard to zoom to the full extent of the image.

4

From the Menu bar (located above the Toolbar), select Views > Reference Map Link. A separate window appears with a map of the image location. The cyan-colored box indicates the extent of the image, and the dot in the middle indicates the image center. The image covers a portion of Central Park in New York City. It contains several softball fields, ponds, and an amphitheater. The large building in the lower-right corner is the Metropolitan Museum.

5

If your mouse has a scroll wheel, use it to zoom in and out of the image. If not, press the F9 key to zoom in or the F10 key to zoom out in fixed increments. The zoom level is displayed in the Toolbar.

6

Zoom into a specific area by clicking the Zoom button in the Toolbar and drawing a box around the area to zoom.

7

Zoom to 100% resolution by pressing the F11 key, or by selecting 100% (1:1) from the drop-down list. The Image window shows the image at its native pixel resolution, with no scaling. Each image pixel is represented by a single pixel on the screen. 2. 8

To pan around the image, click thePan button in the Toolbar. Left-click and drag the mouse to pan. Or, click and drag the middle mouse button or scroll wheel.

9

Click the Rotate View button in the Toolbar. Left-click and drag the mouse to rotate. Or, select a rotation angle from the drop-down list in the Toolbar.

10

Zoom to an area that you are interested in, then select Placemarks > Add Placemark from the Menu bar. A placemark saves the current view and zoom level. 2. 11

In the New Placemark dialog, enter a name for the location and click OK; for example:

The custom location is saved under the Placemarks menu. When you move to another area in the image, you can go back to the saved location by clicking Placemarks and selecting it from the list; for example:

12

Move the cursor around the image and notice that the latitude and longitude coordinates of the cursor location are displayed in the Status Bar at the bottom of the ENVI application. The Status Bar contains three horizontal segments. By default, the first (left) segment displays geographic coordinates, and the second segment displays the map projection of the image. The third segment is blank.

13

Right-click in the first (left) segment and select Raster Data Values. The red, green, and blue data values are displayed for the current pixel location; for example:

14

Zoom to full resolution (100%) in the image, then click the Overview check box in the Layer Manager. The Layer Manager is located near the upper-left corner of the application. A small yellow Overview Window is displayed in the upper-left corner of the view.

15

Pan around the image. The red box in the Overview Window shows the extent of the current view location, relative to the entire image. 2. 16

Uncheck the Overview option to hide the Overview Window.

This concludes the quick guide. When you are finished, exit ENVI.

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