Warp and Resample

ENVI offers three warping options for image-to-map registration: RST, polynomial, and Delaunay triangulation. The resampling methods include nearest neighbor, bilinear, and cubic convolution.

Reference

J.A. Richards, 1999, Remote Sensing Digital Image Analysis Springer-Verlag, Berlin, p. 240.

See the following sections:

• Warp and Resample Image-to-Map
• Warp from GCPs: Image-to-Map

Warp and Resample Image-to-Map

1. Select the ground control points (GCPs).

2. In the Ground Control Points Selection dialog, select Options > Warp Displayed Band or Options > Warp File.

   The options Warp Displayed Band (as Image to Map) and Warp File (as Image to Map) are also available from the Ground Control Points Selection dialog when selecting image-to-image GCPs.

• If you select Warp Displayed Band, the Registration Parameters dialog appears.
• If you select Warp File, the Input Warp Image dialog displays. Select the input warp file and click OK. The Registration Parameters dialog appears.
3. In the Output Projection and Map Extent area of the Registration Parameters dialog, set the output projection for the image:
• To change the projection of the upper-left coordinate only, click Change Proj.
• To change the map coordinates or latitudes/longitudes for the upper-left coordinate, use the X Pixel Size, Y Pixel Size, Output X Size, and Output Y Size fields.
• Click Options and select from the menu to manage the output projection and map extent settings.
4. In the Warp Parameters area of the Registration Parameters dialog, select the warping and resampling methods.
5. Click OK. ENVI adds the resulting output to the Available Bands List.

Warp from GCPs: Image-to-Map

Use Warp from GCPs: Image to Map to perform image-to-map registration without having the images displayed. Use GCPs you selected previously to perform the registration.

1. From the Toolbox, select Geometric Correction > Registration > Warp from GCPs: Image to Map Registration. The Enter GCP Filename dialog appears.
2. Select a .pts file and click OK. The Image to Map Registration dialog appears. See Image to Map Registration for the remaining steps.