Generate Ground Control Points

Instructions for Use

Ground Control Point (GCP) refers to control points located at specific positions and on particular targets within an image, possessing coordinate information in the mapping coordinate system. Due to their high-precision spatial coordinate data, GCPs are used in processes such as geometric correction of remote sensing imagery, positioning accuracy verification, and spatial registration to achieve high-precision georeferencing and positional tracking of image data.

SuperMap iDesktopX11i(2023) version starts to support this feature.

Parameter Description

Parameter Name Parameter Interpretation Parameter Type
Dataset

Displays the dataset containing the imagery used for generating ground control points. This field is not editable.

DatasetMosaic
Input Image Type Select the type of imagery used for generating ground control points. The default is Panchromatic Image. It can also be switched to Multispectral Image, Forward-looking Image, Rear-view Image, or Front View and Rear View Image based on specific circumstances. ComboBoxImageType
Error Threshold The error threshold for outlier removal in image matching, with a range of [0,40]. The default is 5, and the unit is px. During image matching, the least squares method is used to fit the result points, removing points that exceed the error threshold. A larger threshold retains more tie points but increases the probability of preserving incorrect points. Double
Point Distribution Mode

Select the ground control point distribution mode. Two options are provided: Conventional and Uniform. The default is Conventional.

  • Conventional: Divides each overlapping area into N*M sub-regions, then selects n image blocks of 512*512 size from each sub-region for tie point matching to ensure stable and reliable tie points. The generated ground control points will cover the entire overlapping area as much as possible.
  • Uniform: The generated ground control points will be evenly distributed across the overlapping area. The number of points is fewer than that in the regular distribution, but the distribution is more uniform, making it suitable for images with significant internal distortion.
PointDistributionMethod
Density

Available when Conventional is selected in Point Distribution Mode.

Divides each overlapping area into N*M sub-regions and sets the intensity for generating ground control points: Sparse corresponds to 3*3 sub-regions; Medium corresponds to 4*4 sub-regions; Dense corresponds to 6*6 sub-regions. The default is Medium. Higher density requires longer computation and processing time.

ImageMatchPointDensityLevel
Matching Method

Available when Conventional is selected in Point Distribution Mode.

Five matching methods are provided: MOTIF, AFHORP, RIFT, SIFT, and DEEPFT. The default is MOTIF. Among these, AFHORP and RIFT support multi-modal data matching, while DEEPFT requires configuring an AI model and installing CUDA.

  • MOTIF: A template matching algorithm for multi-modal imagery, characterized by using lightweight feature descriptors. MOTIF can overcome nonlinear radiation distortions caused by differences between SAR and optical images.
  • AFHORP: A feature matching algorithm for multi-modal imagery. AFHORP is highly resistant to radiation distortion and contrast differences in multi-modal imagery and performs excellently in addressing issues like directional reversal and abrupt phase extreme changes.
  • RIFT: A feature matching algorithm robust to large-scale nonlinear radiation distortions. RIFT not only enhances the stability of feature detection but also overcomes the limitations of using gradient information for feature description.
  • SIFT: A method for extracting unique invariant features from images, used for reliable matching of objects or scenes under different viewpoints.
  • DEEPFT: An image matching method based on deep learning.
ImageMatchMethod
Maximum Points per Block

Available when Conventional is selected in Point Distribution Mode.

The maximum number of points retained per image block during image matching. The range is [25,2048], and the default is 256.

Integer
Number of Seed Points

Available when Uniform is selected in Point Distribution Mode.

Sets the number of seed points for tie point matching on each image. The range is [64,6400], and the default is 512. When the image texture is poor, it is recommended to increase the number of ground control points to ensure sufficient matching points and improve subsequent imagery quality.

Integer
Seed Point Search

Available when Uniform is selected in Point Distribution Mode.

Sets the method for searching seed points. The default is Raster Center Point.

  • Corner Points: Uses points with distinct features within the selected region as seed points.
  • Raster Center Point: Uses the center point of the raster as the seed point. This search method is random.
SearchSeedPointMethod
Template Size

Available when Uniform is selected in Point Distribution Mode.

Sets the interval size between seed points. The range is [1,256], and the default is 40, with the unit being px. A larger template size results in more reliable search points but requires more time.

Integer
Search Radius

Available when Uniform is selected in Point Distribution Mode.

Sets the search radius for seed points during image matching. The range is [0,256], and the default is 40, with the unit being px. A larger search radius increases the matching range but also requires more time.

Double
Semantic Culling of Non-Ground Points Not selected by default. When selected, AI semantic technology is used to automatically remove ground control points in cloud areas and building areas. Boolean
Cloud Area

Available after selecting Semantic Culling of Non-Ground Points.

Selected by default. This means ground control points within cloud areas will be automatically removed based on the set dataset. If not selected, ground control points in cloud areas will be retained.

Boolean
Dataset

Displayed after selecting Cloud Area and is not editable.

For workflows related to DOM production, use the cloud amount data in Set Image Path.

For workflows related to DSM production, use the cloud amount data in Set Image Path (DSM/DEM).

DatasetVector
Building Area Available after selecting Semantic Culling of Non-Ground Points. Selected by default. This means building areas will be automatically identified, and ground control points in these areas will be removed. If not selected, ground control points in building areas will be retained. Boolean

Output Result

Generates a GroundControlPoint vector point dataset in the Control Point data source.

Related Topics

Set Image Path

Set Image Path (DSM/DEM)

Generate Tie Points

Block Adjustment