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Unfortunately, ENVI's tools for exporting ROIs to ASCII and for importing ROIs from ASCII are not designed to work together. As you've seen, if you export an existing ROI to an ASCII file, ENVI will output information for every pixel inside that ROI, regardless of whether it's a polygon, point, or polyline ROI (or a combination of those).
When you use the tool in the ROI Tool under ROI_Type > Input Points from ASCII, ENVI expects that you will choose an ASCII file that gives only the vertices for the ROI you wish to create. So, if you want to import a rectangular ROI from an ASCII file, you will need to build that file yourself, entering x and y coordinates for every vertex in your polygon. The last vertex should be identical to the first vertex. That is how ENVI will know that the polygon is done.
- Peg
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