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Simon,<br>
<br>
If you set the configuration option GTIFF_POINT_GEO_IGNORE to "TRUE"
instead of the default "FALSE" the offset will not happen.<br>
<br>
I've tested this and it works. The configuration option needs to be
set in code, it is not a GTiff creation option.<br>
<br>
I'm not quite sure why you need to do that. Anyway it happens when
the destination geotiff is created and its fields are set. The
geotransformation of the geotiff file are set indirectly using
geotiepoints using the geotransformation of the source (which is
correct).
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<br>
<br>
Ari<br>
<br>
<div class="moz-cite-prefix">On 19.11.2015 10:24, Simon Lyngby
Kokkendorff wrote:<br>
</div>
<blockquote
cite="mid:CANzGYpQjcHFM-i7T92dx-Y-6WuU8MqAo6ROdi+3bJ4Q1LfCYQA@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>
<div>
<div>Basically it seems to be an issue with interpreting
"center" directives when doing the gdal_translate.
Consider:<br>
<br>
ncols 2<br>
nrows 2<br>
xllcenter 0.0<br>
yllcenter 0.0<br>
cellsize 1.0<br>
nodata_value -999<br>
2 2<br>
2 2<br>
<br>
</div>
gdalinfo on this file, will give the expected
GeoTransform:<br>
<br>
In [2]: ds = gdal.Open("center.asc")<br>
<br>
In [3]: ds.GetGeoTransform()<br>
Out[3]: (-0.5, 1.0, 0.0, 1.5, 0.0, -1.0)<br>
<br>
</div>
<div>Seems OK to me.<br>
</div>
<div><br>
</div>
If I then do a gdal_translate: gdal_translate center.asc
center.tif, I get another interpretation:<br>
<br>
In [4]: ds = gdal.Open("center.tif")<br>
<br>
In [5]: ds.GetGeoTransform()<br>
Out[5]: (0.0, 1.0, 0.0, 1.0, 0.0, -1.0)<br>
<br>
</div>
And, if I do a roundtrip: gdal_translate -of AAIGRID
center.tif center_back.asc, I get:<br>
ncols 2<br>
nrows 2<br>
xllcorner 0.000000000000<br>
yllcorner -1.000000000000<br>
cellsize 1.000000000000<br>
NODATA_value -999<br>
2 2<br>
2 2<br>
<br>
</div>
Which is definitely not the same GeoTransform as my input
center.asc, but shifted half a cellsize from what I would
expect...<br>
<br>
In [6]: ds = gdal.Open("center_back.asc")<br>
<br>
In [7]: ds.GetGeoTransform()<br>
Out[7]: (0.0, 1.0, 0.0, 1.0, 0.0, -1.0)<br>
<br>
<br>
<br>
GDAL version: <br>
<div>GDAL 1.11.2, released 2015/02/10<br>
<br>
</div>
<div>Cheers,<br>
</div>
<div>Simon<br>
<br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Nov 18, 2015 at 9:38 PM, Simon
Lyngby Kokkendorff <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:silyko@gmail.com"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:silyko@gmail.com">silyko@gmail.com</a></a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div>
<div>
<div>
<div>
<div>
<div>
<div>Hi List,<br>
<br>
</div>
I have a geoid in AAIGRID-format, with the
following header:<br>
<br>
ncols 1001
<br>
nrows 731
<br>
xllcenter 400000.0
<br>
yllcenter 6045000.0
<br>
cellsize 500.0
<br>
NODATA_value 9999<br>
<br>
</div>
GDAL will read this just fine, and report:<br>
<br>
Driver: AAIGrid/Arc/Info ASCII Grid<br>
Files: dkgeoid13b.utm32<br>
Size is 1001, 731<br>
Coordinate System is `'<br>
Origin =
(399750.000000000000000,6410250.000000000000000)<br>
Pixel Size =
(500.000000000000000,-500.000000000000000)<br>
Metadata:<br>
AREA_OR_POINT=Point<br>
Corner Coordinates:<br>
Upper Left ( 399750.000, 6410250.000) <br>
Lower Left ( 399750.000, 6044750.000) <br>
Upper Right ( 900250.000, 6410250.000) <br>
Lower Right ( 900250.000, 6044750.000) <br>
Center ( 650000.000, 6227500.000) <br>
Band 1 Block=1001x1 Type=Float32,
ColorInterp=Undefined<br>
NoData Value=9999<br>
<br>
</div>
As expected, the upper left corner is shifted half
a pixel. It is my understanding, that GDAL
(GetGeoTransform) always uses the xulcorner,
yulcorner (pixel) interpretation. However, I was
suprised to see that after a <br>
<br>
gdal_translate dkgeoid13b.utm32 hello.tif, I get:<br>
<br>
>gdalinfo hello.tif<br>
Driver: GTiff/GeoTIFF<br>
Files: hej.tif<br>
Size is 1001, 731<br>
Coordinate System is `'<br>
Origin =
(400000.000000000000000,6410000.000000000000000)<br>
Pixel Size =
(500.000000000000000,-500.000000000000000)<br>
Image Structure Metadata:<br>
INTERLEAVE=BAND<br>
Corner Coordinates:<br>
Upper Left ( 400000.000, 6410000.000) <br>
Lower Left ( 400000.000, 6044500.000) <br>
Upper Right ( 900500.000, 6410000.000) <br>
Lower Right ( 900500.000, 6044500.000) <br>
Center ( 650250.000, 6227250.000) <br>
Band 1 Block=1001x2 Type=Float32, ColorInterp=Gray<br>
NoData Value=99<br>
</div>
<br>
The GeoTransform is not shifted half a pixel, and is
not the same as the AAIGRID i ran gdal_translate
on?? So, I would have to interpret now the
GeoTransform as xulcenter and yulcenter. This came
as a suprise, and led to some bugs in our processing
software.<br>
<br>
</div>
Is this to be expected??<br>
<br>
</div>
Cheers,<br>
</div>
Simon Kokkendorff<br>
<div>
<div>
<div> <br>
<div> <br>
</div>
</div>
</div>
</div>
</div>
</blockquote>
</div>
<br>
</div>
<br>
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