Creating a DSM from External Sources

فاطمة اسعد طيب. م.م

To create a DSM in Stereo Analyst, the following information is required: • Projection, spheroid, and datum • Average flying height above ground level used to acquire the imagery • Rotation order—three rotation angles (that is, Omega, Phi, and Kappa) • Photo direction—the photo direction defines whether the images are aerial or ground-based (that is, terrestrial images). If aerial images are used, the photo direction is the Z-axis. If groundbased images are used, the photo direction is the Y-axis.

Creating a DSM from External Sources

• Two overlapping images

• Camera calibration—this is information such as focal length and principal point offset in the x and y direction

• The six interior orientation coefficients for each image

• The six exterior orientation parameters for each image

What is a Block File?

A block file is a file containing two or more images that form a DSM. In most block files, there are more than two images; therefore, you can choose from a number of different image combinations to view in stereo. Moreover, a block file contains information such as sensor or camera type, projection, horizontal and vertical units, angle units, rotation system, photo direction, and interior and exterior orientation information. When this information is provided to Stereo Analyst, the need for parallax adjustment in the Digital Stereoscope Workspace is eliminated. Stereo Analyst utilizes the accurate sensor model information to automatically adjust parallax to provide a clear DSM.

Steps to creat DSM

1. Select and display the left and right images.

Load the LA Data

Add a second image

• From the File menu of the Digital Stereoscope Workspace, select Open -> Add a Second Image for Stereo.

• In the Select Layer To Open dialog, navigate to the directory where you loaded the images and select the image la_right.img.

• Click OK to generate pyramid layers for this image too.

The two images currently displayed in the Main View are not parallel to your eye base. For this reason, the images must first be rotated so that they are parallel to your eye base.

2. Open the Create Stereo Model dialog

From the toolbar of the Digital Stereoscope Workspace, click the

Create Stereo Model icon

You can also open the Create Stereo Model dialog by selecting

Utility -> Create Stereo Model Tool.

Create Stereo Model dialog

In the Create Stereo Model dialog, click the Block filename icon The Block filename dialog opens.

Click in the File name field and type the name la_create, then press Enter on your keyboard. The .blk extension (block file) is automatically appended.

3.Enter Projection Information

• In the Create Stereo Model dialog, click the Projection icon . The Projection Chooser dialog opens.

In The Custom tab of the Projection Chooser dialog : Projection Type: UTM

Spheroid Name: GRS 1980 Datum Name: NAD83

UTM Zone: 11 NORTH or SOUTH: NORTH

Click OK in the Projection Chooser dialog to transfer the information to the Create Stereo Model dialog.

In Create Stereo Model dialog : Map X,Y Units: meter

Cartesian Units: meter

Average Height: 3925 meters

Angular Units: degree

Rotation Order: Omega, Phi, Kappa

Photo Direction: Z Axis

When you have finished, the Common tab of the Create Stereo Model dialog looks like the following:

4.Enter sensor model parameters

• Enter Frame 1 Information:

• Image filename: la_left.img

• Interior Affine Type: Image to Film

• Camera Units: Millimeters

• Focal Length: 154.047

• Principle Point xo: 0.002

• Principle Point yo: -0.004

Using the following table, type the six coefficient values for la_left.img into the Interior tab.

Add Interior and Exterior Information for Frame 2, la_right.img

When you have finished, the Frame 2 tab of the Create Stereo Model dialog looks like the following.

5. Save the block file

In the Create Stereo Model dialog, click the Apply button.

Once the Apply button has been selected, all of the image sensor model information is saved to the block file.

Click the Close button to dismiss the Create Stereo Model dialog. In the Digital Stereoscope Workspace, click the Clear Viewer icon

6. View the block file.

• Click the Open icon in the Digital Stereoscope Workspace.

• In the Select Layer To Open dialog, click the Files of type dropdown

list and select IMAGINE OrthoBASE Block File (*.blk).

Navigate to the directory in which you saved la_create.blk.

• Click OK The block file you created, la_create.blk, displays in the Digital Stereoscope Workspace.

Adjust the x-parallax as necessary to improve the appearance of the DSM.