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Adjustment Options for ortho mapping drone and scanned imagery

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.

Parameter settingDescription

High

GPS accuracy is 0 to 10 meters, and the tool uses a maximum of 4 by 3 (twelve) images. This is the default value.

Medium

GPS accuracy of 10 to 20 meters, and the tool uses a maximum of 4 by 6 (twenty four) images.

Low

GPS accuracy of 20 to 50 meters, and the tool uses a maximum of 4 by 12 (forty eight) images.

Very Low

GPS accuracy is more than 50 meters, and the tool uses a maximum of 4 by 20 (eighty) images.

Maximum Residual

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.

Compute ground control points

You can use a reference image to calculate ground control points (GCPs). When choosing a reference image for GCP computation, make sure your reference image has good georeferencing quality in terms of geopositional accuracy and clarity, and the resolution is similar to your source imagery. For example, the default ArcGIS Online world imagery service may be a good reference for computing GCPs for your satellite data, but will likely not be a good reference for high resolution and highly accurate aerial imagery.

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