To Remove Raster Data Outside a Rectangle

1. Click Raster menu CropRectangular Region.
2. Select a point that represents one corner of the rectangular crop region. A rubber-band line is displayed to help you establish the angle.
3. Pick a point at one corner of the raster data you want to preserve.
4. Pick a third point to define the final size of the rectangular region to preserve. The image is cropped to this region, and the image frame follows the edge of the cropped region.