Available with Advanced license.
The parameters used in computing the block adjustment are defined in the Adjust window. The appropriate adjustment options are presented depending on the type of workspace defined when you set up your ortho mapping project. For example, triangulation is performed using EXIF data collected with drone imagery.
Adjustment options for drone data
The block adjustment settings specific for drone imagery are described below.
Quick adjust at coarse resolution only
If this option is checked, adjustment will be performed at a coarse, user-defined resolution. This coarse adjustment is done quickly and allows you to review the data coverage for your project area and the processing parameters for the collection before running the more accurate, refined adjustment at the source image resolution. For example, when you collect data in the field, you can use this option for an initial assessment of the adjustment, then run Adjust again to compute the refined adjustment. If this option is not checked, tie points are computed at source image resolution, and triangulation is performed using the computed tie points.
Perform Camera Calibration
Automatic calibration is used to compute and improve the camera’s geometric parameters, including interior orientation and lens distortion, while determining image orientation and image ground coordinates. If the camera has not been calibrated, such as many cameras for collecting drone imagery, it is recommended that you check on all the following options to improve the overall quality and accuracy of bundle block adjustment. All options are selected by default. For more information on calibration parameters, see Camera table schema.
- Focal Length—Refines the focal length of the camera lens
- Principal Point—Refines the principal point of the autocollimation
- K1,K2,K3—Refines the radial distortion coefficients
- P1,P2—Refines the tangential distortion coefficients
Note:Camera calibration will be performed during block adjustment to improve the camera parameter accuracy. Camera calibration requires that your image collection have an in-strip overlap of 60 percent or more and a cross-strip overlap of 30 percent or more.
Fix image location for high-accuracy GPS
This option is used only for imagery acquired with high-accuracy, differential GPS, such as Real Time Kinematic (RTK) or Post Processing Kinematic (PPK). If this option is checked, the process will only adjust the orientation parameters of the imagery and leave GPS measurements fixed. Additionally, Ground Control Points (GCPs) are not required when this option is checked. GCPs will be marked as check points in the adjustment.
Blunder Point Threshold (in pixels)
Tie points with a residual error greater than the threshold value will not be used in computing the adjustment. The measurement unit of the residual is pixel.
Note:Higher in-strip and cross-strip aerial image overlap is recommended for better block adjustment and product generation results.
Image Resolution Factor
This parameter is used to define a resolution at which match points will be computed and the initial adjustment performed. The range of values is between full resolution and 8 times the resolution of the source imagery.
The default value of 8 times the source image resolution is suitable for most imagery that includes a diverse set of features. A smaller value such as 4 or 2 can be used for imagery with ubiquitous features, such as sand, water, or agricultural areas, where match points are difficult to compute at coarser resolution.
Image Location Accuracy
Image location accuracy indicates the accuracy level of your GPS data collected concurrently with your imagery and listed in the corresponding EXIF data file. The values consist of 4 airborne GPS accuracy levels that are used in tie point calculation to determine the number of necessary overlapping images. For example, when the accuracy is set to High, the algorithm will use a smaller neighborhood to identify matching features in the overlapping images.
The GPS accuracy is 0 to 10 meters. A maximum of 4 x 3 images will be used for tie point matching. This is the default value.
The GPS accuracy is 10 to 20 meters. A maximum of 4 x 6 images will be used for tie point matching.
The GPS accuracy is 20 to 50 meters. A maximum of 4 x 12 images will be used for tie point matching.
The GPS accuracy is more than 50 meters. A maximum of 4 x 20 images will be used for tie point matching.
Drone imagery tutorial
For a guided tutorial on the full drone imagery workflow, see Create Drone Imagery Products.