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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>So in the end, what are the proposed changes from the users point
of view (in rtpostgis.sql)? Sorry I have been away a bit.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Pierre<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
postgis-devel-bounces@postgis.refractions.net
[mailto:postgis-devel-bounces@postgis.refractions.net] <b>On Behalf Of </b>David
Zwarg<br>
<b>Sent:</b> 10 septembre 2010 11:35<br>
<b>To:</b> PostGIS Development Discussion<br>
<b>Subject:</b> Re: [postgis-devel] WKTRaster Scale and Skew<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal>On Fri, Sep 10, 2010 at 11:16 AM, Pierre Racine <<a
href="mailto:Pierre.Racine@sbf.ulaval.ca">Pierre.Racine@sbf.ulaval.ca</a>>
wrote:<o:p></o:p></p>
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<p class=MsoNormal style='margin-bottom:12.0pt'>> Width is computed
based on scale & skew?<o:p></o:p></p>
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<p class=MsoNormal>In 99% of the cases there is no rotation and pixel width
& height ARE synonyms for scale X and scale Y. Is it worth changing their
names? Adding confusion? How does GDAL name it?<o:p></o:p></p>
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<p class=MsoNormal><br>
I agree that 99% of the time, there is no rotation. I don't propose
changing the names of the pixel width methods, just change the way it is
computed to account for the skewing. I wouldn't mind hiding the
set_skews() method, in favor of accepting all adjustments in the form of the
georeference string. This is the way GDAL gets around it -- they don't
name the 6 components of the georeference, and just note that "In case of
north up images, the GT(2) and GT(4) coefficients are zero" -- not much
help if you want to know what happens when north is not up.<br>
<o:p></o:p></p>
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<p class=MsoNormal style='margin-bottom:12.0pt'><br>
>We don't call it scaleX and scaleY, but cell_width_x and cell_height_y<br>
>We don't call it skewX and skewY, but cell_width_y and cell_height_x<o:p></o:p></p>
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<p class=MsoNormal>In rt_api.c? Why not...<o:p></o:p></p>
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<p class=MsoNormal style='margin-bottom:12.0pt'><br>
>We separate the accessors for the pixel width and the georeference
component that is now used as the width.<o:p></o:p></p>
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<p class=MsoNormal>You mean creating a "truepixelwidth" function?
Same reluctance since it is not really a width when the pixel shape is a
diamond. But you could say "this happen only 0.001 of the time"...
Does that mean removing or renaming the ST_PixelSizeX and ST_PixelSizeY
function?<o:p></o:p></p>
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<p class=MsoNormal><br>
I would propose some other name besides pixel 'width', since it's only a part
of the width. Maybe we don't have any accessors for this value at all,
and the only way to get it is through the georeference string?<br>
<o:p></o:p></p>
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<p class=MsoNormal style='margin-bottom:12.0pt'><br>
>Tests assume the upper left coordinate is SMALLER in the X and GREATER in
the Y for all other coordinates in the raster -- this would require adjusting
our tests to handle the coordinate space uniformly.<o:p></o:p></p>
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<p class=MsoNormal>Ok.<br>
<br>
My main concern is to not confuse users with scale, skew and width. Most people
know only pixelsize.<o:p></o:p></p>
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<p class=MsoNormal><br>
I agree -- it took me a few minutes to understand that the parameters are not
exactly width or scale or skew. This may be sacrilege, but what if all
that was hidden under the hood, and we just provide the true width/height get
functions and the get/set functions for the georeference? Because most of
the time, nobody will care about the skew.<br>
<br>
Thoughts?<br>
Zwarg<br>
<o:p></o:p></p>
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<p class=MsoNormal><br>
Pierre<br>
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<a href="http://postgis.refractions.net/mailman/listinfo/postgis-devel"
target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-devel</a><o:p></o:p></p>
</blockquote>
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