Why are my ROIs and/or vector layers shifted on my image?

 

You may notice working with an image defined in an arbitrary (unknown) projection that when you superimpose vectors or ROIs on the image, the ROIs and/or vectors exhibit a shift from their real position. This Help Article discusses a possible workaround to fix this behavior.

When an image projection is defined as arbitrary, it means the projection is unknown and the pixel positions are based on image coordinates rather than map coordinates. If the image has a defined Xstart and Ystart value in the image header, these values are subtracted from the X and Y pixel coordinates of the vectors or the ROIs in ENVI.
This causes a shift in the ROI and/or vector positions on the image.

To workaround this problem, set the Xstart and Ystart in the image header to 0 before superimposing the ROIs or vectors on the image. This can be accomplished through the menu File ->Edit ENVI Header in ENVI Classic or from the  Edit ENVI Header tools from the ENVI Toolbox.

Note: The default value for Xstart and Ystart is 1 for an arbitrary projection in ENVI.

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Reviewed by BC on 09/17/2014