The parameters used in computing the block adjustment are defined in the Adjustment Options dialog. 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 and scanned aerial data
The block adjustment settings specific for digital drone imagery and scanned aerial photographs are described below.
Initial Tie Point Resolution Factor
The Initial Tie Point Resolution Factor is used to define a resolution at which the initial adjustment will be performed. This parameter is used by the Quick Adjust tool as well as Adjust tool if you run it directly without running Quick Adjust. The range of values is between full resolution to 8 times the source resolution.
The default value of 8 times the source resolution is suitable for most imagery that includes a diverse set of features. A smaller value such as 4 or 3 can be used for imagery with ubiquitous features such as sand, water, agricultural areas where match points are difficult to compute at 8 times the reduced resolution.
GPS location accuracy
GPS location accuracy indicates the accuracy level of your GPS data collected concurrently with your imagery, and listed in your corresponding EXIF data file. The values consist of 4 levels which are used in the tie point calculation algorithm to determine number of images in neighborhood to use.
GPS accuracy is 0 to 10 meters, and the tool uses a maximum of 4 by 3 (twelve) images. This is the default value.
GPS accuracy of 10 to 20 meters, and the tool uses a maximum of 4 by 6 (twenty four) images.
GPS accuracy of 20 to 50 meters, and the tool uses a maximum of 4 by 12 (forty eight) images.
GPS accuracy is more than 50 meters, and the tool uses a maximum of 4 by 20 (eighty) images.
Tie points with a residual error greater than the Maximum Residual value will be not be used in computing the adjustment. The measurement unit of the residual is pixel.
Perform Camera Calibration
Camera calibration is performed to identify and correct for image distortions induced by the sensor system. The camera's internal parameters, including focal length, principal point, and lens distortion parameters are used to produce a camera correction model. This information is used to compute the interior orientation, which is the relationship between the imaging plane and the sensor platform. ArcGIS supports camera calibration of many commercial cameras, which are selected when you create your workspace.
If your camera is not available as a supported camera type, you can calibrate your camera during block adjustment to improve the camera parameter accuracy. The automatic camera calibration requires that your image collection has in-strip overlap of more than 60% overlap, and cross-strip overlap of more than 30%. Check on Perform Camera Calibration to compute the camera calibration. This is the default.