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Reproject Images

Reproject Images

Use Reproject Raster to reproject georeferenced images to another projected coordinate system. ENVI performs a reprojection by first converting the input dataset's map extents into the selected output coordinate system to determine the output map extents. Based on the warping method that you specify, any number of pixels in the input dataset are reprojected into an output raster dataset using the reprojected map extents and the selected output coordinate system.

You can also use this tool to convert from a rational polynomial coefficient (RPC) model, pseudo projection, or geographic lookup table (GLT) to a standard Geographic Lat/Lon WGS-84 projection. In these cases, the input and output coordinate system strings can be the same.

You can also write a script to reproject images using the ENVIReprojectRasterTask routine.

  1. Click Browse to select a raster dataset that you want to reproject. See Supported File Types for a list of accepted raster formats. You can optionally select a spatial or spectral subset instead of the entire image.
  2. The Reproject Raster tool displays the input dataset's upper-left tie point, x/y pixel sizes, and x/y output sizes (lines and samples, respectively). Click Options to display the upper-left tie point as degrees/minutes/seconds, decimal degrees, or linear units.

  3. Click Select Output Coordinate System. Refer to Select a Coordinate System for instructions on choosing a pre-defined or custom coordinate system. When you are finished, the Reproject Raster tool updates the upper-left tie point, pixel sizes, and output dimensions, based on the new coordinate system, and it displays the selected coordinate system properties.
  4. From the Resampling drop-down list, select a method for interpolating the input pixels to the output raster dataset. The options are Nearest Neighbor (default), Bilinear, and Cubic Convolution. The cubic convolution method is the most accurate but also the slowest.
  5. From the Method drop-down list, select a warping method. The choices are Polynomial (default), Triangulation, and Rigorous. The rigorous method is the most accurate because it reprojects every pixel in the input image, but it is also the slowest.
  6. If you selected the Polynomial or Triangulation method, enter the number of pixels for sub-sampling the output dataset in the Grid Spacing field. The default value is 25, meaning that every 25th pixel in the x- and y-direction will be reprojected and the remaining pixels will be interpolated.
  7. Enter a pixel value in the Data Ignore Value field that represents the output image background value. All pixels outside of the warped-image boundary will be set to this value. The default value is 0.
  8. Choose a file format and location for the reprojected dataset.
  9. Note: Not all coordinate systems are available for use with TIFF output. If you receive an error message when choosing TIFF output, select ENVI as the output format instead.

  10. Enable the Display Result option to load the resulting image into the display after processing is complete.

See Map Information for more information on how ENVI manages map information in different raster layers.

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