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Bas Retsios wrote:<br>
<blockquote type="cite" cite="mid47419ED6.9020205@itc.nl">
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The x and y as mentioned in formula [1] (4.4.4), the so-called
"intermediate coordinates" are the scan-angle of the satellite. There
is a linear relationship between the c and l (column and line of a
pixel in an MSG-image), and the angle at which this was "seen" from the
satellite.<br>
<br>
Since c and l also have a linear relationship with X and Y (meters, in
GEOS projection), you must be right when you say that there is also a
linear relationship (scaling + offset) between (x,y) and (X,Y).<br>
<br>
Calculate the relationship, given the following:<br>
<br>
The ColumnDirGridStep and LineDirGridStep values found in the header
files of the MSG images are 3004.03165817 m for bands 1-11, and
1000.134348869 m for HRV band 12. Thus not exactly 3km / 1km, but
slightly more. These values have never changed, since our institute
installed a receiver for MSG images in 2004.<br>
<br>
For bands 1-11, COFF=1856 and CFAC=-13642337, and for band 12, COFF =
5566 and CFAC=-40927014. These values have also remained the same for
all images up to now.<br>
<br>
c = COFF + x * CFAC / 65536<br>
c = X / ColumnDirGridStep</blockquote>
The last part is wrong .. of course you need to add COFF to get c, thus:<br>
c = COFF + X / ColumnDirGridStep<br>
<br>
Therewith, the relationship between x and X is a factor:<br>
<br>
x * CFAC / 65536 = X / ColumnDirGridStep<br>
<br>
thus<br>
X = x * CFAC * ColumnDirGridStep / 65536<br>
and<br>
x = X * 65536 / (CFAC * ColumnDirGridStep)<br>
<br>
Best regards,<br>
<pre class="moz-signature" cols="72">--
Ir. V. (Bas) Retsios
Software Developer
Geo-information Processing Department
International Institute for Geo-information Science and Earth Observation (ITC)
P.O. Box 6, 7500 AA Enschede, The Netherlands
Phone +31 (0)53 4874 573, telefax +31 (0)53 4874 335
E-mail <a class="moz-txt-link-abbreviated" href="mailto:retsios@itc.nl">retsios@itc.nl</a>, Internet <a class="moz-txt-link-freetext" href="http://www.itc.nl">http://www.itc.nl</a>
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