Matt,<div><br></div><div>Affine transform and GCPs are the two methods used to set the georeference of a raster. These two are practically exclusive of each other. You cannot use Affine transform because your images they are not exactly rectangular. Your only option is setting GCPs.</div>
<div><br></div><div>Since you are using WGS84, the X and Y values indicate the longitude and latitude of the pixel's position.</div><div><br></div><div>Please go through the GDAL Data Model page[1] so that you don't miss any other details.</div>
<div><br></div><div>[1]: <a href="http://www.gdal.org/gdal_datamodel.html">http://www.gdal.org/gdal_datamodel.html</a></div><div><br><div class="gmail_quote">On Fri, Oct 7, 2011 at 3:35 AM, matt.feemster <span dir="ltr"><<a href="mailto:matt.feemster@ga-asi.com">matt.feemster@ga-asi.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">Long time GDAL user here, but first time poster.<br>
<br>
I have an image in an internal format that I want to save out as a GeoTiff.<br>
>From all of the examples I've seen, they say to use a transformation matrix.<br>
However, we cannot do that with our images because they are not exactly<br>
square. When using a transformation matrix, they come out skewed.<br>
<br>
What we ideally need to do, is simply save the corner coordinates of the<br>
original image in the GeoTiff (similar to how a NITF is done). We already<br>
know what they are in our original format, but I cannot figure out how to<br>
properly assign them using GDAL.<br>
<br>
I have tried setting the GCPs with no luck, so I feel like I am missing<br>
something.<br>
<br>
So my question involves three steps:<br>
<br>
1) Is it possible to store only corner coordinates as a way of telling<br>
GDAL/GeoTiff what the geo information is for a GeoTiff? Again,<br>
transformations will not work here.<br>
<br>
2) If it is possible, how to go about it?<br>
<br>
3) When assigning the GCPs, what exactly do the 'x' and 'y' members of the<br>
GDAL_GCP structure mean? Per the documentation: X position of GCP in<br>
georeferenced space. Are x and y a lat/lon pair? ECEF x/y? UTM<br>
easting/northing? What exactly should I be assigning these values.<br>
<br>
<br>
Assume WGS84 for everything.<br>
<br>
Any help would greatly be appreciated. I've burned two solid days on this<br>
task and am out of ideas.<br>
<br>
Thanks.<br>
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</font></blockquote></div><br><br clear="all"><div><br></div>-- <br>Best regards,<br>Chaitanya kumar CH.<br><br>+91-9494447584<br>17.2416N 80.1426E<br>
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