Tuesday, July 21, 2009

Reprojecting Compressed Images

Have you ever had a very large compressed image you needed to reproject? The challenge is, you do not want to reproject to a new uncompressed version of the image file and then re-compress.

Have you used Calibration in ERDAS IMAGINE?

Let’s say you have a 2GB 20:1 MrSID compressed color infrared (CIR) image you need to deliver to an ArcGIS user in your organization. The last thing you want to do is resample and re-compress, right? That takes too much disk space and time.

Display the image in the Viewer, select Raster > Geometric Correct > Reprojection. On the dialog that appears, select the new projection and then select the ‘ruler’ on the Geo Correction Tools dialog to calibrate the image.

This process will create a .aux for you MrSID file storing the mathematical model to reproject the image on-the-fly.

Deliver both the MrSID image and the .aux file to your ArcGIS friend. That as fast and simple.

  1. Starting ERDAS IMAGINE 9.2+, the IMAGINE MrSID encoders write full projection information to the MrSID header. WKT strings are written to MG2, and WKT strings and GeoTIFF tags to MG3 data.
  2. With this change, the need for .sdw files and .aux files for map and projection data are no longer needed, but are available.

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