You collect accuracy-control points by selecting a point in a reference image, comparing it with the location of the point in an overlapping working image, and then using that point. That is, your objective is to open two overlapping images, compare the point location in each, and then relocate the point in the working image, as necessary.
To collect accuracy-control points
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In the Image-to-Ground Computation window, edit the value in the Point ID box, if necessary.
That is, the point ID is generated automatically. You can type a new value; however, each point (ground control point, check point, tie point, and elevation-match point) in the image must have a unique ID.
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If necessary, clear the Auto locate check box.
Note: That is, the Auto locate check box is selected by default. With this check box selected, the corresponding feature in the overlapping image will be centered automatically in the viewer. If you do not want the feature centered automatically, clear the check box.
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In the Open Image window, select the first image you want to use, and then click Open.
The image displays in the viewer.
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In the Open Image window, select the second, overlapping image you want to use, and then click Open.
A new instance of the viewer appears, displaying the image you selected.
Tip: Position the viewer windows so you can view each simultaneously onscreen.
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In the viewer displaying the first image you opened, click the crosshair of the point you want, and then click Use Point.
The Image-to-Ground Computation window is updated automatically with the relevant image IDs, pixel-and-line positions, and computed ground coordinates of the first image.
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In the viewer displaying the second image, observe the location of the corresponding point.
Tip: If the corresponding point is not in proximity to that of the reference image, in the preview pane of the viewer displaying the working image, you can drag the image footprint (red rectangle) to the area of interest (AOI), and then zoom in to view precisely the AOI.
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If the location of the point in the second image does not match that of the first, drag the point to a location that matches that of the first image, and then click Use Point.
The Image-to-Ground Computation window is updated automatically with the relevant image IDs, pixel-and-line positions, and computed ground coordinates of the second image.
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In the Image-to-Ground Computation window, click Accept.
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Repeat steps 2 to 7 for each point you want to verify, as necessary.
That is, open a pair of images, compare the location of the points, and then, if necessary, make changes to the location of the point in the second image of the pair.