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Live DEM Editing

PCI Geomatics -

The DEM Editing tool is a quick and easy tool created to smooth out irregularities and create a more accurate model, and in turn, generate more accurate orthorectified images.

Using the Focus DEM Editing window requires only a DEM; that is, a raster channel in a writable format. To fully use all the functionality available in the DEM Editing window, however, and to produce the best possible DEM, the DEM file should contain additional information. In particular, if the DEM file was extracted from epipolar images, you can make use of that imagery to help with your editing.

The DEM Editor does not require special 3D viewing technology as the work is done in a mono viewing environment. The tool automatically regenerates both stereo ortho images in user defined regions to inspect for vertical accuracy. This allows you to quickly generate the ortho images in different areas of your DEM to quickly spot check what the output ortho image will look like in more complex terrain. Being able to identify errors that may negatively affect your output Ortho-Mosaic can save you significant time and money, as you can address problems in the DEM prior to the ortho- mosaicking process.

There are two separate sections to the tutorial below. The first section is a short demo which will get you familiar with the Live DEM Editing windows and process. The second section is a more in depth demo outlining how to use multiple polygons to edit a DEM.

Data for this tutorial is found at the following link: http://dl.pcigeomatics.com/Marketing/GeomaticaDemos/Focus/LiveDEM_Aerial.zip (5.37GB)

 

Demo 1 – Quickly Editing an Urban Area

1. Open the Geomatica 2014 Focus application.

 

2. Load the DEM into Focus by dragging and dropping the file into the Maps tab or by clicking File > Open. Notice the default view is grayscale.

 

3. In the Focus menu bar, click on the Layer dropdown menu and select DEM Editing.

 

The Live DEM Editing window should open and your DEM should now be rendered as a dynamic pseudo-color hillshade.

 

NOTE: The Display DEM button lets you switch between a colored shaded relief DEM view and the ortho preview. An ortho preview is a preliminary ortho mosaic that’s been created using the digital terrain model calculated when you created the DSM.

4. Using the Zoom In tool in Focus, zoom into an area you wish to edit. You will notice that the preliminary ortho mosaic shows some issues. The rooflines are not straight and there is some blurring around trees. Using the DEM editor we can flatten the elevation and create a better looking ortho.

 

 

5. Click on the Create a polygon layer button.

 

6. Using the New Shapes tool in Focus, digitize a polygon around the dwellings you want to edit.

 

7. In the DEM Editing window choose Terrain filter (flat), Size 100 (search radius), Gradient 40%


8. Click Apply. You will notice that the dwellings have been removed as we have averaged out the elevation with the ground.

 

9. In the DEM Editing window, click on the Define Preview Region button

 

10. Draw a polygon around the area that has been edited. The Full Res: Ortho Preview window will open.



NOTE: Loading the area at 1:1 gives you a view of the end ortho mosaic that will be generated once you decide to create an ortho of the area.

 

11. In the Full Res: Ortho Preview window you can click on the Left and Right drop down arrows. This will let you choose between different views for the output ortho.
When you compare the filtered ortho preview to the unfiltered ortho preview in the Focus window you will notice the building outlines are now straight and the trees are no longer smeared. This is a result of removing the distortion and averaging out the elevation values.

 

 

12. The edited DEM can now be saved using the Save icon in the DEM Editing window. At this point the DEM has been accurately edited so that it can be used for a variety of applications such as orthorectification and mosaicking.

 

Demo 2 – Fixing a Bridge in a DEM

In the following tutorial we will be editing some elevated bridges and ramps.

1. Open the Geomatica 2014 Focus application.

 

2. Load the DEM into Focus by dragging and dropping the file into the Maps tab or by clicking File > Open.


 

2. In the Focus menu bar, click on the Layer dropdown menu and select DEM Editing

 

3. The Live DEM Editing window should open and your DEM should now be rendered as a dynamic pseudo-color hillshade.

NOTE: Clicking on Display DEM will change the DEM view from a colored DSM view to an ortho preview. Ortho preview is a preliminary ortho mosaic created using the digital terrain model of the surface terrain model.

 

Editing the Elevated Bridges and Ramps

The area of interest for this tutorial will be the bridge and ramp shown in the image below.

 

1. In the DEM Editing window, ensure that the Edit via Polygons tab is the active tab and click on the Open Polygon Layer button

 

2. Select the polygon layer in the list (DEM Editing Polygons)


3. Click OK

 

4. A vector layer is added to the map containing a set of polygons that follow the bridges we will be editing. Use the following figure to identify each polygon by a number.

 

5. On the Focus toolbar, click on the Selection Tool

 

6. Select polygon 1


7. In the DEM Editing window, change the Operation to Road Median Filter


8. Change the Size to 50


9. Click Apply with Overwrite


NOTE: The Apply with Overwrite allows the DEM operation to be applied to all pixels under the selected polygon. This includes pixels covered by another polygon. The Apply with Overwrite tool is used here, because polygon 3 has a segment that intersects polygon 1. Since polygon 1 is the bridge on top, we need to use the Apply with Overwrite.

 

10. Select polygon 2

We are using the Road Medium filter with the same settings as on polygon 1

11. Click Apply with Overwrite
12. Select polygon 3
13. Click Apply

Polygon 3 is the lower bridge segment, therefore we click Apply (Not Apply with overwrite) so that we do not overwrite the elevation information of the bridges above.


NOTE: Ctrl+Z can always be used to undo an accidental edit

14. Select polygon 4
15. Click Apply with Overwrite

The bridges and ramps in this area should now be accurate and smooth. We now need to clean up underneath the bridge.

 

Editing The Road Under The Bridges and Ramps

1. In the DEM Editing window, ensure that the Edit via Polygons tab is the active tab and click on the Open Polygon Layer button

 

2. Select the second polygon layer in the list (RoadFix)
A new set of polygons will be added to the map. The figure below provides numbers for each of the polygons.

Polygon 1 and 2 are not used for any editing in this step. They are used to prevent the operation performed on polygon 3 to overwrite the information on polygon 1 and 2.
 

3. Using the Selection tool, select polygon 3


4. In the DEM Editing window, change the Operation to Opposite ends fill


5. Click Apply. The road underneath polygon 1 and 2 is now cleaned up.

 

6. In the DEM Editing window, ensure that the Edit via Polygons tab is the active tab and click on the Open Polygon Layer button


7. In the Select Layer window, click on the File dropdown list and select bridgefix_vec.pix


8. Select the third polygon layer in the list (BottomRoads)


9. Click OK



Polygons 1, 2 and 3 are not used for any editing in this step. Rather, they are used to prevent the operation performed on polygon 4 and 5 to overwrite the information on polygons 1, 2 and 3.


10. Using the Selection tool, select polygon 4


11. In the DEM Editing window, change the Operation to Opposite ends fill (if it is not already set)


12. Click Apply. The mess along the road under polygon 4 is cleaned and the road is now smooth.


13. Using the Selection tool, select polygon 5


14. In the DEM Editing window, change the Operation to Opposite ends fill (if it is not already set)


15. Click Apply. The mess along the road under polygon 5 is cleaned and the road is now smooth. This DEM now accurately represents the elevations and slopes of the interchange. The result of your edits should look similar to the following diagram.



 

Viewing a Defined Region

1. Make sure that you are displaying the DEM with surface (manmade) features removed from the plateau


2. In the DEM Editing window, click on the Define Preview Region button

 

3. With the tool selected, draw a bounding box in roughly the same area as displayed in the figure directly below (red box)

 

4. In the 1:1 Ortho Preview window, click the Flicker Left/Right Image button

The left and right stereo images will begin flickering back and forth in the Full Res: Ortho Preview window.

The edited DEM can now be saved using the Save icon in the DEM Editing window. At this point the DEM has been accurately edited so that it can be used for a variety of applications such as orthorectification and mosaicking.

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