Ground Control Points may optionally be added in the Pixel-to-Points tool to adjust the horizontal and vertical positioning of the point cloud. With no ground control points, the point cloud will be positioned using the input image metadata.
Ground Control Points identify recognizable features in the input images, and align them to a known location (X,Y and Z coordinates). Typically the point cloud is aligned based on surveying of these identifiable features, however the ground control point location could also be identified by loading other reference data, such as surveyed assets or reference ortho-rectified imagery, such as those available from Online datasources.
Enter ground control points on the right side of the Pixels-to-Points tool dialog.
To add a ground control point, press the New Point... button on the right side of the Convert Images to Point Cloud [BETA] dialog, under the image preview.
Enter the location of the Control Point using one of the options in the Location section. Optionally specify the Elevation, name and custom symbol to use for the Ground Control Point.
From the Input Image files list, select each of the input images, so that they display in the Image Preview. Click on the Image Preview to zoom in on the clicked location. When the Ground Control point is located press the Add Point to Image... button and click the Ground Control location on the input image preview. The mouse wheel may also be used to zoom in and out on the preview image.
Complete this process for each of the input images. Then add at least two more Ground Control Points, and locate them in each of the images.
When a Ground Control Point is selected from the list, all of the input images that contain that control point will display in blue text. Right click on the Ground Control point list for additional options to move between input images. The Ground Control Points will also show the number of identified image matches in the # Points column.
Once the control points have been added, optionally right click on the Ground Control Points list for additional options to check the specified points, including previewing them in the main map window.
Enter the known coordinates of the ground control point. Double-click the named point in the Ground Control Points list to bring this dialog back up for an already added Ground Control point.
Name- Specify a name to identify the ground control points.
Symbol - This is the point symbol that will be displayed on the image previews that contain this ground control point.
Elevation - The elevation value is important to vertically align the output point cloud. The default vale will come from the image metadata, but should be customized for improved vertical accuracy.
Location - Specify the coordinate location of the ground control point. The current projection is set from the Configuration display projection, and if no data is loaded into the map it will default to Geographic WGS84. The Select From Map... button will also be available in the location section, only when there is data loaded in the main map view.
Press this button to add a control point to the current image preview. It may be necessary to first click on the image to zoom, or use the mouse wheel to zoom in on the image preview.
Press the remove selected button to remove the entire Ground Control Point from the list of Ground Control points.
To remove the point from only one input image, press the point to select it. Then press the Delete key to remove the Ground Control Point instance.
Right-click on the Ground Control Points list to see the following options:
Once the tool has been run with specified Ground Control Points, the Input Image list will populate with columns of additional statistics based on the fit of the input control points. This final complete operation dialog will also display the overall camera position fit error.