Juan:
Some responses below:
Well, that's exactly the problem, i cannot make a complete mosaic for the
region i'm working on with only images taken on one day, and it adds another
problem: the images do not overlay well... if they did, i would been able to
do a radiometric normalization easily (as Johnattan Greenberg suggested)...
By "do not overlay well" I assume you mean they aren't well
orthorectified to one another -- although I consider this a "must do"
for mosaicking and for any level of image-to-image work (because of the
time savings), you COULD manually pick PIFs in the overlap zone (e.g.
you'd pick a point in the reference image, then visually pick the
corresponding pixel in the uncorrected image) -- orthorectifying first
saves you the time of having to pick two points per image -- rather, you
just pick one point. How many images do you have in your mosaic?
Image-to-image rectification with landsat imagery is fairly painless,
shouldn't take you much more than 30 mins per image once you get going
with it.
At any rate, once you pick your PIFs, you can use v.what.rast or
starspan (starspan.casil.ucdavis.edu) to get this data out to a table to
do the regression calculations.
So my problem now is how to overlay landsat images taken in different days.
I've already asked for help on this issue (with no solution so far; mail
subject="mosaic with landsat geotiff"), so guess i'll resume that thread...
if it is simply an "automatic contrast" adjustment, you could linearly
interpolate between bands so they matched. (but then which is correct?) I
don't think it would be though, as LANDSAT has fixed calibration for each
band.
How's that?
This is what I suggested as well -- the question of which one is
"correct" is somewhat moot -- your goal, as I understand it, is to have
all of the images in the same radiometric scale, so you can just pick
one (usually one that's in the middle of your mosaic, and often
temporally at the "edge" of your time period (either a very early or a
very recent image). If
if you run i.landsat.rgb on the two images with the same parameters do they
match up well?
what do you mean with 'the same parameters'? (maybe "cropping intensity"...)
that doesn't touch the values, only the colors, but it may
give you a clue about the cause of the difference.
How exactly? as an example, i can see a subtle difference in the color of
water in a river as it pases on to another 'tile', but what does it means, i
don't have a clue... (the values changes from: |32|40|86| to |20|26|69|, for
bands 3, 2, 1 respectively)
I guess the important thing is the ratio of the bands, not the exact values
of one particular band. I take it you see a hard line at the boundary in
the processed image?
i suspect you mean the same as Johnattan G. with the radiometric
normalization... anyway, i don't know what you mean with 'proccesed image'.
The original images come with a null region as a result of the
georreferencing, and after i use r.null -r to remove the NULL-value bitmap
file, yes, there is a hard line in the boundary, but what would that mean?
It just means your images aren't radiometrically normalized to one
another. If you correctly normalize them you won't see a line in the
mosaic.
Hamish
JM
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--
Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
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Davis, CA 95616
Cell: 415-794-5043
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