| How to use Envi GLT when there are NaNs in the lat/lon files? [message #60278] |
Thu, 08 May 2008 10:10  |
envi35@yahoo.ca
Messages: 48
Registered: March 2005
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Member |
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Hi, I'm trying to georeference an image covering a very large area -
pixels in the ocean were given as NaN. This image was projected, but I
was not able to set up its projection in Envi based on the available
parameters. However, there are lat/lon files for all of the grid
points in the image. So I thought I could use GLT to register the
image myself. Then there are NaNs in the lat/lon files same as in the
image file. Does anybody have expereince of applying GLT from lat/lon
with missing values? Is this possible?
Thanks for any advice,
Jenny
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| Re: How to use Envi GLT when there are NaNs in the lat/lon files? [message #60413 is a reply to message #60278] |
Tue, 13 May 2008 03:55  |
wita
Messages: 43
Registered: January 2005
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Member |
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On May 8, 7:10 pm, Jenny <env...@yahoo.ca> wrote:
> Hi, I'm trying to georeference an image covering a very large area -
> pixels in the ocean were given as NaN. This image was projected, but I
> was not able to set up its projection in Envi based on the available
> parameters. However, there are lat/lon files for all of the grid
> points in the image. So I thought I could use GLT to register the
> image myself. Then there are NaNs in the lat/lon files same as in the
> image file. Does anybody have expereince of applying GLT from lat/lon
> with missing values? Is this possible?
>
> Thanks for any advice,
>
> Jenny
Jenny,
I've never tried to use the GLT in ENVI but my guess is that you need
to
filter out the NaN in all three images and write them to a new ENVI
image.
These images can then be used as input to the GLT module.
In pseudo code:
image = envi_get_data('imagefile')
lat = envi_get_data('latitudefile')
lon = envi_get_data('longitudefile')
; Asssuming NaN values are on the same locations in all files
index = Where(Finite(image) EQ 1, c)
IF c gt 1 THEN BEGIN
nimage = image[index]
nlat = lat[index]
nlon = lon[index]
ENDIF
writeu, nmimage
writeu, nlat
writeu, nlon
envi_setup_head, nimage, nb=1, nr=1, nc=N_Elements(image)
envi_setup_head, nlat, nb=1, nr=1, nc=N_Elements(image)
envi_setup_head, nlon, nb=1, nr=1, nc=N_Elements(image)
Then use the nimage, nlon and nlat images as input to the GLT module
as described in the ENVI manual.
ENVI's GLT module will then put the data on the right place based on
the corresponding lat/lon values.
Allard
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