3D Control Point Report

Function Overview

Provides two inspection methods: elevation and XYZ.

When selecting elevation, the control point report tool generates a report on the elevation differences between the LiDAR point cloud and ground control points. This can be used to check the elevation accuracy of the LiDAR point cloud and improve its elevation accuracy using the calculated correction values. The output report shows the elevation differences between the used LiDAR point cloud and the elevation control points, as well as statistical information like the average magnitude of elevation differences, mean error, root mean square error, average elevation difference, and the maximum and minimum elevation differences.

When selecting XYZ, the control point report tool calculates elevation and horizontal differences based on the identified target positions. It generates a report on the elevation and horizontal differences between the LiDAR point cloud and the ground control points, which can be used to check the elevation and horizontal accuracy of the LiDAR data. The output report shows the elevation and horizontal differences between the used LiDAR point cloud and the elevation control points, as well as statistical information like the average magnitude, mean error, root mean square error, average elevation difference, and the maximum and minimum values.

Target refers to a ground marker made of special materials with specific patterns and shapes, typically placed in areas lacking distinctive features. It is used for accuracy checks in LiDAR and ground control in aerial photography. Targets can automatically identify their positions in point clouds or images, obtaining the 3D coordinates of the marker points or the image pixel coordinates, thereby reducing manual operations.

Target Types
Four types of targets are supported:

Square Checkerboard: A square black and white checkerboard pattern, with the target positioning point located at the center of the target.

Circular Checkerboard: A circular black and white checkerboard pattern, with the target positioning point located at the center of the circle.

2-Layer Concentric Circles: Consists of two concentric circles with alternating black and white colors. The outer circle is black, the inner circle is white, and the radius of the outer circle is twice that of the inner circle. The target positioning point is at the center.

3-Layer Concentric Circles: Consists of three concentric circles with alternating black and white colors. The outer circle is black, the middle circle is white, and the innermost circle is black. The radius of the outermost circle is three times that of the innermost circle, and the middle circle's radius is twice that of the innermost circle. The target positioning point is at the center.

The control point file is a text file separated by commas or spaces, with each line containing X, Y, and Z information. At least three control points are needed to successfully create a control point report.

Usage

Click Strip Alignment > 3D Control Point Report

Choose the elevation check method if only control points are available. When targets are set up, you can choose the XYZ check method.

Elevation Check Method

Select the control point file path in ASCII format. A dialog for control point file reading settings will pop up, where you can set the columns for X, Y, and Z, and the number of skipped rows. After selecting, click Apply.

Click the Calculate button. Once the calculation is complete, you can double-click any row in the control point table to jump to the location of the control point. You can use the Profile Tool for a more intuitive view of the relative positions between control points and the point cloud.

After the calculation, you can select the corresponding control points or modify the maximum slope and maximum triangle edge length, then click the "Calculate" button to recalculate.

Parameter Settings

Input Point Cloud Data: The input file can be a single point cloud data file or a point cloud dataset.
From Class (default "All Available Categories"): The user needs to select the point cloud category to check the elevation accuracy using control points, generally choosing hard surface point clouds like ground points and building points.
Z Tolerance (default "0.15"): Point cloud Z direction accuracy, to avoid excessively small distances between point clouds causing large slopes.
Max Slope (degrees) (default "45"): The maximum terrain slope tolerance. If the slope exceeds this value, the elevation difference will not be calculated. Control points are generally placed on relatively flat terrain, so excessive slopes are prone to erroneous information.
Max Triangle (meters) (default "20"): The maximum triangle length to avoid large deviations caused by elevation interpolation. A large triangle edge length indicates too few points in the From Class of the control point corresponding point cloud area, resulting in significant errors in the calculated elevation difference.
Control Points: Input the control point file.
Control Point Size (default "5"): The size of control points displayed in the window when double-clicking on data in the control point report list to locate the corresponding control points.
Dz Limit (default "3"): Set the Dz tolerance. If not within this tolerance range, it is displayed in red to detect significant elevation differences between the LiDAR point cloud and control points. Maximum tolerance = average elevation difference + Dz limit × mean error; minimum tolerance = average elevation difference - Dz limit × mean error.
Export Separator: Set the separator for exporting the control point report, including semicolons and commas.
Calculate: After setting the parameters, click this button to calculate the elevation difference.
Export: Export the control point report in txt format. The exported file contains the elevation error information of the point cloud data and statistical information of Dz, separated by the specified separator.

XYZ Check Method

Feature Description: After importing the control points, identify targets based on their positions.

Feature Description: Select targets. If targets are not identified based on control points, manually identify the target center position in the viewer by adjusting the correlation parameters between the point cloud and the target.

Feature Description: Delete target. Delete the selected row's target in the table.

Feature Description: Modify target position. Adjust the target position in the table by fine-tuning the coordinates in the pop-up interface.

Feature Description: Delete target. Delete the selected row's target in the table.

Parameter Settings

Point Cloud to Target Correlation (default "0.85"): Point cloud Z direction accuracy to avoid excessively small distances between point clouds causing large slopes.
Dz Limit (default "3"): Set the Dz tolerance. If not within this tolerance range, it is displayed in red to detect significant elevation differences between the LiDAR point cloud and control points. Maximum tolerance = average elevation difference + Dz limit × mean error; minimum tolerance = average elevation difference - Dz limit × mean error.
Dxy Limit (default "3"): Set the Dxy tolerance. If not within this tolerance range, it is displayed in red to detect significant horizontal differences between the LiDAR point cloud and control points. Maximum tolerance = average elevation difference + Dxy limit × mean error; minimum tolerance = average elevation difference - Dxy limit × mean error.

Transformation Relationship Save

The elevation check method provides four types of calculation methods for Height Fitting based on the calculation results: plane fitting, linear interpolation, quadratic surface fitting, and cubic surface fitting. The XYZ check method additionally provides Four Parameters Calculation, Seven Parameters Calculation, 3D Affine, and linear transformation. The linear transformation is based on the calculated delt X, delt Y, delt Z from the identified target positions and control point positions.

Feature Description: Calculate transformation relationship.

Feature Description: Save transformation relationship.

Refer to Create Transformations.

3D Control Point Report