Using ground control points, tie points, or elevation match points to generate a digital elevation model

OrthoEngine uses the math model solution (known exterior orientation) and the pixel and line positions of the points in common in the overlapping images to generate a digital elevation model (DEM), which is saved as a PCIDSK file (.pix). The elevations are calculated from the parallax between the corresponding ground control points (GCPs), tie points, and elevation match points in the images.

The DEM can be fairly accurate for relatively flat areas, however, it is not recommended for rough areas since you would have to collect a large number of points to accurately represent the terrain.

On the Elevation Match Point Collection window, the Point ID is generated automatically. You can type a new label in the Point ID box, however, all points (ground control points, check points, tie points, and elevation match points) in the image must have unique labels.
You can select Auto locate to aid with collection.
In the Photo Layout window under Overview, double-click the crosshairs of two overlapping images.
Choose a feature that appears in both images. At a zoom level where you can see the detail in one of the images, position the cursor precisely on the feature and then click Use Point. At a zoom level where you can see the detail in the second image, position the cursor precisely on the same feature and then click Use Point.
Click Accept.
To edit a point, click the point under Accepted Elevation Match Points. Under Image Positions, click Quick Open beside the image that you want to edit. Reposition the cursor precisely on the feature, click Use Point, and then click Accept.
Click:
- Create DEM to generate a DEM from the points. When Include GCP & Tie Points to Build DEM? appears, click Yes if you want to use the project's ground control points and tie points to generate the DEM.
- Add to DEM to add the points to an existing DEM. This is useful if you want to add more points to an area where you are not satisfied with the results.
- Save to File to save the points to an ASCII file. Type the path for the file that you want to add the points to or click Browse to select a file. Click Create. If the text file exists, you can click Append to add the points to the end of the file or click Delete to remove the file and create a new one.
Click Close.