Clipping and subsetting images

Before creating a subset or a clip, you should consider the output format. A subset file is based on the file type of the source file by default. You can change the output format of a subset to any GDB-compatible data type. For some file types you may want to add or remove information. The Clipping/Subsetting process lets you choose the file data type for a clip or subset with the GDB Options Editor.

When you have selected a file, you can work with the Available Layers list. The list of layers depends on the output format you have chosen. For example, if you select a format that only supports vector data (for example, SHP format), only vector layers are listed.

Note: If vector georeferences are not compatible with the source file, vectors in the segment are not clipped. A warning message shows a list of incompatible vector segments. Georeferencing is compatible when they are equal, or when one is an under specified form of the other.

If your data has an associated Rational Function math model segment containing Rapid Positioning Capability (RPC) data, you can include this segment in your clipping operation. If an RPC Rational Function model segment is available for clipping, it will be listed under "Binaries" in the Available Layers list.

Note: Other segment types, including LUT, GCP, and PCT, can also be transferred to the output file but will not be clipped.

When using the Clipping/Subsetting feature, you must specify the bounds of a clip or subset and then run the process.

From the Clipping/Subsetting window, choose a file from the File list box in the Input area, or click Browse to select the file. The image is displayed in the Clipping/Subsetting view pane along with any Enhancement setting that is applied to the image in the Focus view pane.
From the Available Layers list, select the layers and, if applicable, any associated RPC Rational Function math model segment, that you want to clip.
A check mark indicates the layers and segment (if applicable) that will be clipped.
In the Output area, choose a file from the File list box.
- If the file is not listed, click Browse and choose a file from the File Selector window.
- If you want to use the Select a Script Subset File option available from the Definition Method list, you can leave the File box empty.
Select the file format that you want for the output from the Format list box. If you want to select specific options for the format, click Options and select options from the GDB Options Editor.
Enter a value that you want to use for pixels without data in the output file in the Initialization Value box. Use a value that does not occur in the image being clipped. If you want to give the initialization value the metadata tag of no data, select the Set as No Data Value check box.
If you want to save the defined clip region boundary as a vector layer in the output file, select the Output Clip Boundary Vector check box.
Depending on how you want to use to clip the image, select one of the following options from the Definition Method list box:
- User-entered Coordinates: enters the corner coordinates for the clip region. All layers will be clipped to fit that region.
- Select a File: uses a smaller, intersecting file to define the bounds of a subset.
- Select a Clip Layer: uses a smaller, intersecting layer from a file to define the bounds of a subset.
- Select a Named Region: bases the clip on a named region you created in Focus.
- Select a Script Subset File: creates several clip regions on the same image. You can create a text file containing the coordinates and the output file name; Focus automatically produces the series of subset files.
- Use Current View: bases the clip on the region displayed in the view pane. Only available from Area view.
Click Clip.