Frederick,
I'm a geophysicist but never thought that an earthquake could have that
side effect of image referencing.
Anyway the horizontal deformation caused by a big earthquake is of the
order of meter scale. One idea I had is that you can use the shift grid
to to relocate previous GCPs and than use those relocated ones in
gdalwarp. You can compute 'old' GCPs by interpolating your images both
for pixels and metric (UTM) units. The operations would be something
like this
1. Get "px py old_UTMx old_UTMy" by interpolating the referenced image
at a certain well distributed positions
2. apply the shift grid to old GCPs and get new GCPs "px py new_UTMx
new_UTMy"
2. re-register with gdalwarp and new GCPs
Of course, this is in absence of a more straight solution where the
shift grid is applied directly to the images.
Joaquim Luis
Hi,
I am working here in Chile and we have a lot of earthquakes here, the last
big one like a year ago. So the problem is that I have a lot of
georeferenced images, but georeferenced before the earthquake. We thought
the best way would be to calculate a shift grid and apply it with gdalwarp
to all of the images. The only thing I would have to do is to apply the grid
from one datum to the same datum instead of from one datum to another, this
should be possible, shouldn´t it?
Reading a lot in the mailing-list I found a link to an australian
govermental site, where they provide a program to convert from NTv2_ASCII to
NTv2_GSB. So I created an Ntv2_ASCII file with our shift values and
converted it with this program to an .gsb-file and tried to apply that file
with gdalwarp to our images. But no matter what I tried, nothing happened,
the shift never was applied. I saw a lot of examples of possible commands
searching in the mailing-list and tried everyone, also in nearly every
possible combination but nothing lead to an applied shift. So I am a bit
desperate right now, hoping someone can help me a bit or give an advice.
Here in short what I have to do:
Apply a shift grid from UTM 18s WGS84 to UTM 18s WGS84 in order to apply the
coordinate changes of our images owing of the earthquake last year.
I would apreciate any kind of help and thank a lot in advance,
Frederick
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