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<p class=MsoNormal>Hi,<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I have a question about handling of coordinate system
information in FDO when only an SRID number is known.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The general problem is that there are cases where a
provider’s data store contains SRID numbers for a coordinate system, but
does not have WKT information or other catalog information to provide any more
details on the coordinate system. So, when a client asks for the coordinate
system information for that geometry property (via spatial context) what
information should be returned? There are two fields relevant here, the
coordinate system name and the coordinate system WKT. (There is also the
spatial context name.)<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Let’s say that for a given geometry property, the
provider only knows that the SRID is 2955. We could assume that when there is
an SRID number that it is an EPSG code (btw, 2955 is utm zone 11n). That would
be correct most of the time, but I don’t know if we can guarantee in
general that that’s what it is since systems that don’t have a
coordinate system catalog don’t enforce any particular numbering
convention for SRID numbers (e.g. MySQL, SQL Server 2008 geometry type).<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Options:<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>(1)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Csname = ‘2955’, wkt = null.<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>(2)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Csname = ‘EPSG:2955’, wkt = null.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>To provide any WKT values would require adding capabilities
to the provider to access a catalog either using a coordinate system package
(e.g. Proj4), or an internal look up table of SRID to WKT. So far, we have
avoided requiring that providers access coordinate system packages internally
(unless they had native support such as with Oracle). The next two options fall
into this category.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>(3)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Include a look up table from SRID to WKT – could
be a file that a user could update.<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>(4)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Include access to a coordinate system library from
within the provider.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Does anyone have any preferences or other alternatives? If
we choose one of the first 2 options, it would mean that existing client
application code should change to recognize the pattern. Options 3 and 4
introduce additional dependencies to providers. For option 4, note a discussion
on fdo futures on client-side libraries for coordinate system support ( <a
href="http://trac.osgeo.org/fdo/wiki/FdoClientUtilities"><span
style='color:windowtext;text-decoration:none'>http://trac.osgeo.org/fdo/wiki/FdoClientUtilities</span></a>
).<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Currently, I think some providers do return the csname of ‘EPSG:2955’
pattern, but it’s not consistent across providers and not specified
explicitly. I’d like to have a specified consistent behavior.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Let us know if you have any thoughts about this.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks,<o:p></o:p></p>
<p class=MsoNormal>Orest.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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