When it is necessary to perform classified display of existing ground control points to understand error distribution, or manually add/edit ground control points to improve accuracy, these operations can be achieved through the Manage Ground Control Points function. Specific features include filtering, editing, adding, deleting, sorting, importing field-acquired control points, and classified display. This article focuses on filtering, editing, classified display, and field-acquired control point import functions.
For management convenience, the program uses two independent datasets to manage control points from different sources:
- Collect Control Points dataset: Manages field-acquired control points.
- Automatically Generate Control Points dataset: Mainly stores control points automatically generated through the Generate Ground Control Points function.
When opening the Manage Ground Control Points function, the Collect Control Points dataset is managed by default. You can switch between datasets using the Control Point Dataset dropdown in the management window.
Manage Ground Control Points is only available when both original image and reference image exist.
Supported since SuperMap ImageX Pro 11i(2023) version.
Feature Entry
Imagery Tab->Geometric Correction Group->Generate Tie Points Dropdown->Manage Ground Control Points.
Filter
Used to filter control points that meet specified conditions in the attribute table. Three filtering methods are provided:
- Current Map Extent: Attribute table only displays control points within current map extent.
- Match Image: Check one or multiple images to display control points associated with specified images.
- SQL Expressions: Filter control points using custom SQL expressions.
Edit
Select a row in the attribute table and click the Edit button in the toolbar to open the Edit dialog. Use the Select, Add, Edit, Confirm Point, and Delete functions in the dialog toolbar to add new points or adjust point positions. Click the Confirm Point button to save changes after editing.
Three map browsing functions are provided for convenient viewing and editing: Pan, Linked Views, and Full View.
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| Figure: Edit Control Points |
Classified Display
After control points participate in adjustment, classified display can be performed based on error results.
Check the Classified Display checkbox and click the Settings button to open the Error-based Classified Display dialog. Customize classification display effects by setting error sources, number of classes, and class range values.
- Error: Set error source. Default is Image Space X Direction Residual. Other options include Image Space Y Direction Residual, Object Space X Direction Residual, Object Space Y Direction Residual, and Elevation Residual.
- Number of Classes: Set the number of classification levels. Default is 3, with options for 2, 4, or 5 classes.
- Classification Settings: Display Marker Style, Ranges, and Classification Interval for different classes. Only Ranges are editable.
Figure: Classified Display
Import Field-Acquired Control Point
When reference image accuracy is insufficient for project requirements during remote sensing imagery production, importing high-precision field-acquired control points can enhance result data accuracy. This method effectively compensates for reference image deficiencies and ensures final results meet required precision standards.
Main steps:
- In the Manage Ground Control Points window, click the Import Field-Acquired Control Point button to open the Collect Control Points dialog.
- Configure parameters:
- Control Point File: Select *.txt, *.xls, or *.xlsx files containing control point information. The first four columns must follow "Serial Number", "Longitude", "Latitude", "Elevation" order to ensure proper data matching.
Figure: Control Point File - Source Coordinate System Settings: Set the coordinate system used during field collection to ensure accurate coordinate conversion to the dataset's default system.
- X/Y Precision: Positional accuracy in longitude/latitude directions. Default is 1 m. Smaller values increase adjustment weight.
- Z Precision: Elevation accuracy. Default is 1 m. Smaller values increase adjustment weight.
- List: Control points are automatically listed after file selection. Use checkboxes to select points for import. All points are selected by default.
- Control Point File: Select *.txt, *.xls, or *.xlsx files containing control point information. The first four columns must follow "Serial Number", "Longitude", "Latitude", "Elevation" order to ensure proper data matching.
- Click OK to complete import and automatically open the Edit dialog.
- Select the first record in the management window and use the Edit button to adjust image-space coordinates by moving points in original images.
- Repeat step 4 to assign image-space coordinates for all imported control points.
Related Topics
Generate Ground Control Points