There is only one file type that uses the .URT extension:
Utah Raster Toolkit File
Image data file created by the Utah Raster Toolkit, a Unix-based graphics package; stores images using a Run-length encoding (RLE) compression algorithm; used for storing images in an independent format so they can be manipulated and then exported to other image formats.
The Utah Raster Toolkit is a compilation of C source code and programs. It allows users to manipulate raster image data in ways that are commonly required by computer graphics applications.
URT files may also use the .RLE extension.
Updated: July 19, 2010