Hi Frederick,<br><br><div class="gmail_quote">On Wed, Jun 29, 2011 at 1:25 AM, frederick keusch <span dir="ltr"><<a href="mailto:frederick.keusch@digimapas.cl">frederick.keusch@digimapas.cl</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<br>
I am working here in Chile and we have a lot of earthquakes here, the last<br>
big one like a year ago. So the problem is that I have a lot of<br>
georeferenced images, but georeferenced before the earthquake. We thought<br>
the best way would be to calculate a shift grid and apply it with gdalwarp<br>
to all of the images. The only thing I would have to do is to apply the grid<br>
from one datum to the same datum instead of from one datum to another, this<br>
should be possible, shouldn´t it?<br></blockquote><div><br></div><div>Yeah. I'm assuming you know that the grid shifts are applied as a transform on the geocentric coordinates?</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Reading a lot in the mailing-list I found a link to an australian<br>
govermental site, where they provide a program to convert from NTv2_ASCII to<br>
NTv2_GSB. So I created an Ntv2_ASCII file with our shift values and<br>
converted it with this program to an .gsb-file and tried to apply that file<br>
with gdalwarp to our images. But no matter what I tried, nothing happened,<br>
the shift never was applied. I saw a lot of examples of possible commands<br>
searching in the mailing-list and tried everyone, also in nearly every<br>
possible combination but nothing lead to an applied shift. So I am a bit<br>
desperate right now, hoping someone can help me a bit or give an advice.<br>
Here in short what I have to do:<br>
Apply a shift grid from UTM 18s WGS84 to UTM 18s WGS84 in order to apply the<br>
coordinate changes of our images owing of the earthquake last year.<br>
<br>
I would apreciate any kind of help and thank a lot in advance,<br></blockquote><div><br></div><div>First I'd get your grid working with proj4/cs2cs:</div><div><br></div><div>See how it's setup for the US/NZ/CA grids that are available as a companion download</div>
<div><a href="http://trac.osgeo.org/proj/wiki/GenParms">http://trac.osgeo.org/proj/wiki/GenParms</a> describes the +nadgrids parameter to tell proj4 to use it during datum shift.</div><div><br></div><div>Once that's all working...</div>
<div>In the gdal python bindings you need to add " +wktext" to the end of your proj4 string to get it to recognise/use grids.</div><div><br></div><div>Hope that helps a bit,</div><div><br></div><div>Rob :)</div>
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