Use Rotate/Flip Data to perform several standard image rotations, including 0, 90, 180, and 270 degrees with or without transposition. (Here, transpose means that the dimensions of the array are swapped.) Alternatively, you can specify the exact angle of the desired rotation. Rotating images is useful for orienting images before registration.

Note: To flip an image vertically, where the pivot line is a horizontal running through the middle of the image, choose 270 degrees with transpose. To flip an image horizontally, where the pivot line is a vertical running through the middle of the image, choose 90 degrees with transpose.

You can also write a script to flip raster data using the MirrorRaster task. To transpose raster data, use the TransposeRaster task.

  1. From the Toolbox, select Raster Management > Rotate/Flip Data. The Input File dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Rotation Parameters dialog appears. This dialog varies slightly depending on whether you use a standard IDL rotation or an exact rotation angle.

    3. Initially, some letters and numbers are printed horizontally (normal text orientation) in the box in the upper-right corner of the dialog. The orientation of the numbers shows schematically the orientation of the output image with the selected rotation and/or transpose applied.

  3. Select from the following rotation options:
    • To apply a standard rotation (0, 90, 180, or 270 degrees), click Standard and select the rotation.
    • To flip the x and y coordinates of the image, click the Transpose toggle button to Yes.
    • To specify the exact rotation angle desired, enter a value in the Angle field (angles are measured clockwise from horizontal) and press Enter.
  4. Select the resampling algorithm to use to calculate the output image from the Resampling drop-down list. The choices are Nearest Neighbor, Bilinear Interpolation, or Cubic Convolution.
  5. Select output to File or Memory.
  6. Click OK. ENVI adds the resulting output to the Layer Manager.