Available with Advanced license.
The parameters used to compute the block adjustment are defined in the Adjust window. The available adjustment options depend on the type of workspace defined when you set up your ortho mapping project. For example, RPC or polynomial transformation options are available for satellite images.
Block adjustment
The block adjustment parameters for satellite imagery are described below. These parameters are used when computing tie points or ground control points (GCPs) and when computing a block adjustment.
Transformation Type
Three types of transformations are available for adjusting a mosaic dataset.
- RPC—The Rational Polynomial Coefficients will be used for the transformation. This is used for satellite imagery that contains RPC information within the metadata. This is the default.
- POLYORDER1—A first-order polynomial (affine) is used in the block adjustment computation.
- POLYORDER0—A zero-order polynomial is used in the block adjustment computation. This is commonly used when your data is in a flat area.
Advanced Options
The Advanced Options section exposes additional settings that can be used to support the adjustment process. A description of each setting is given below.
Reproject Tie points
A part of the adjustment process includes computing and displaying each tie point at its correct 2D map location. This is an optional step that only supports the visual analysis of tie points with the 2D map view. Following adjustment, the Reproject Tie Points option in the Manage Tie Points drop-down menu must be used.
Note:
When working with large projects with more than 1,000 images, this step can be skipped to reduce adjustment processing duration, without any adverse impact to the adjustment quality.
Tie Point Matching
Tie points are points that represent common objects or locations within the overlap areas between adjacent images. These points are used to improve geometric accuracy in the block adjustment. The Tie Point Matching category in the Adjust tool includes options to support the automatic computation of tie points from overlapping images.
Image Location Accuracy
The inherent positional accuracy of the imagery depends on the sensor viewing geometry, type of sensor, and level of processing. Positional accuracy is typically described as part of the imagery deliverable. Choose the keyword that best describes the accuracy of the imagery.
The values consist of three settings that are used in the tie point calculation algorithm to determine the number of images in the neighborhood to use. For example, when the accuracy is set to High, the algorithm uses a smaller neighborhood to identify matching features in the overlapping images.
| Setting | Description |
|---|---|
Low | Images have poor location accuracy and large errors in sensor orientation (rotation of more than 5 degrees). The scale invariant feature transform (SIFT) algorithm is used, which has a large pixel search range to support point matching computation. |
Medium | Images have moderate location accuracy and small errors in sensor orientation (rotation of less than 5 degrees). The Harris algorithm is used with a search range of approximately 800 pixels to support the point matching computation. This is the default setting. |
High | Images have high location accuracy and small errors in sensor orientation. This setting is suitable for satellite imagery that has been provided with exterior orientation data. The Harris algorithm is used with a small search range to support point matching computation. |
Tie Point Similarity
Choose the tolerance level for matching tie points between image pairs.
| Setting | Description |
|---|---|
Low | The similarity tolerance for the matching imagery pairs is low. This setting produces the most matching pairs, but some of the matches may have a higher level of error. |
Medium | The similarity tolerance for the matching pairs is medium. This is the default setting. |
High | The similarity tolerance for the matching pairs is high. This setting produces the least number of matching pairs, but each matching pair has a lower level of error. |
Tie Point Density
Choose the relative number of tie points to be computed between image pairs.
| Setting | Description |
|---|---|
Low | The fewest number of tie points is produced. |
Medium | An intermediate number of tie points is produced. This is the default setting. |
High | A high number of tie points is produced. |
Tie Point Distribution
Choose whether the output points have a regular or random distribution.
- Random—Points are generated randomly. Randomly generated points are better for overlapping areas with irregular shapes. This is the default setting.
- Regular—Points are generated based on a fixed pattern.
Mask Polygon Features
Use a polygon feature class to exclude areas you do not want used when computing tie points.
In the attribute table of the feature class, the mask field controls the inclusion or exclusion of areas for computing tie points. A value of 1 indicates that the areas defined by the polygons (inside) are excluded from the computation. A value of 2 indicates that the areas defined by the polygons (inside) are included in the computation and areas outside of the polygons are excluded.