Checking the Accuracy of a DSM

فاطمة اسعد طيب. م.م

Steps Of Checking the Accuracy of a DSM

• Select a block file.

• Open the Stereo Pair Chooser.

• Select a DSM.

• Open the Position tool.

• Enter the 3D coordinates of the check points into the Position tool.

• Observe the check point positions in 3D stereo.

• Record the difference between the original 3D check point

• position and the displayed check point position.

1. Open a Block File

From the toolbar of the empty Digital Stereoscope Workspace, click the Open icon .

Navigate to the <IMAGINE_HOME>\examples\Western directory,

then select the file named western_accuracy.blk.

If you wish to view only the overlapping area of the two photographs comprising a DSM, you can set an option to that effect. From the Utility menu, select Stereo Analyst Options. Then, click the Stereo View Options option category. Click to select the Mask Out Non-Stereo Regions option.

2. Open the Stereo Pair Chooser

In the Digital Stereoscope Workspace, click the Stereo Pair Chooser icon . The Stereo Pair Chooser dialog opens.

Click to select row 2 in the ID column. This is the DSM consisting of images 252.img and 253.img. When you have selected that row, the Stereo Pair Chooser looks like the following.

3. Select a DSM.

4.Open the Position Tool

With the stereopair 252.img and 253.img displayed in the Digital Stereoscope Workspace, click the Position tool .

5. Enter the 3D coordinates of the check points into the Position tool.

1. Ensure that the Enable Update button is not checked in the Position tool.

2. Ensure that the Map X,Y option is set to Map.

NOTE: The units of the X, Y, and Z check point positions are determined based on the sensor model information contained in the block file.

3. Type 1.0 in the Zoom field. NOTE: The zoom is approximately 1.0.

4. In the Position tool, double-click the value in the X field and type the

value 478221.57, then press Enter on your keyboard.

5. Double-click the value in the Y field and type the value 4761174.72, then press Enter on your keyboard.

6. Double-click the value in the Z field and type the value 247.24, then

press Enter on your keyboard.

7. Position the cursor over the intersection of the crosshair to see the specific point in the Left and Right monoscopic Views. The cursor on the left and right images comprising the DSM should be centered over the same feature (the intersection of the two roof lines). 8. While viewing in stereo, visually interpret the location of the 3D floating cursor over the feature. The X and Y position should be located at the intersection of the two roof lines. The 3D cursor should be resting on the roof.

6. Observe the check point positions in 3D stereo.

7.Record the difference between the original 3D check point

Compute Z Elevation Accuracy

• Second Check Point: 478067.22, 4761584.73, and 259.96.

• Third Check Point: 477344.68, 4761657.79, and 269.99.

• Fourth Check Point: 477327.95, 4760990.42, and 257.79.

• Fifth Check Point: 477193.83, 4761458.69, and 257.36.

• Sixth Check Point: 477532.93, 4761699.51, and 292.08.

• Seventh Check Point: 478102.12, 4761488.28, and 242.60.

Close the Position Tool

Now that you have checked and recorded the accuracy of the DSM,

you can close the Position tool and close the block file,western_accuracy.blk.