Suppose that I have 3 landsat images with the same datum ( WGS-84 ) and projection system ( UTM, Zone 39N ) as follows:
TM LANDSAT 5 image for July 1987
ETM+ LANDSAT 7 image for July 2001
OLI_TIRS LANDSAT 8 image for July 2013
I have drawn a ROI in TM LANDSAT 5 image for July 1987 and saved it in a .roi file and now I want to use that ROI to subset data via roi for all of the images. But I encounter the following problem:
I have opened all of the images in ENVI in multiple displays, restored the roi and then used the option subset data via roi
when I do this for TM LANDSAT 5 image for July 1987, there's no problem and the action is done completely and I can store subset data to a file but for the remaining two image, I encounter the ENVI error:
There are no available ROIs associated with this input file
What can I do?
Because I'm doing a change detection project, I don't want to draw approximately identical ROI's in multiple images???
And also I think regarding the same coordinate system for all of the images, I should be able to draw a ROI in one image and then use it in other images???
Is that true or maybe I'm thinking in a wrong way???
Best Answer
ROIs in ENVI are stored in pixel-based co-ordinates, with no geographic information at all. The size of the image used to create the ROI is stored in the ROI file, and when you open the ROI list for an image it only displays the currently loaded ROIs that match the image dimensions.
Although your images are all of the same location, in the same projection and with the same datum, they may not be exactly the same size. The Landsat 8 image, for example, will almost certain have a different size - as the resolution for some Landsat 8 bands has changed.
Luckily, there is a simple way to solve this: however, it relies on your images being accurately georeferenced. Trying loading the images into separate ENVI displays, and then create a geographic link between the windows (Tools->Link->Geographic Link). You should then be able to move around within the images and check that they line up properly. If they don't then you'll need to do some image registration (see the Map->Registration menu).
Once you've made sure they're correctly lined up, you can convert your ROIs from one image to be used in the others. To do this, open your Landsat 7 or Landsat 8 image, go to Tools->ROIs->Reconcile ROIs via map and choose the ROI, and it should convert the ROI for use within the Landsat 7 image. Again, by doing a geographic link between the images you can check that the ROI is in the right place.