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Rick Zoolker schreef:
<blockquote
cite="mid:3fcf5fb70708101034j6d68600ay93e9719060360b94@mail.gmail.com"
type="cite">
<pre wrap="">OK, I feel like I've got a fundamental block about how spatial data is
actually used in the real world and how spatially aware databases
actually make use of that data. This is probably quite obvious for
everyone so please bear with me.
I've been playing with a bunch of spatial databases (Oracle, Postgis,
DB2) and from what I can tell, all tend to roughly follow the OGC SFA
spec (Oracle using different terminology). Now it also seems that the
SFA spec deals EXCLUSIVELY with Cartesian coordinates. </pre>
</blockquote>
Is that so? I haven't noticed using lat/lon being an issue. All my
projects in postGIS are in lat/lon and that tends to work fine. I have
also been using MI Spatialware and Oracle Spatial and as far as I
recall, lat/lon is no issue although in these environments we where
still using the dutch cartesian system.<br>
<blockquote
cite="mid:3fcf5fb70708101034j6d68600ay93e9719060360b94@mail.gmail.com"
type="cite">
<pre wrap="">Now here's my
first confusion. If they only deal with Cartesian coordinates, why do
they allow you to specify SRIDs that are lat/long based. Will any of
the SFA functions work with lat/long (other than ST_Transform(), which
is actually a SQL/MM and not even included in SFA)??
</pre>
</blockquote>
They will. I am using the BBOX functions, but no advanced functions
yet, but I am confident.<br>
<blockquote
cite="mid:3fcf5fb70708101034j6d68600ay93e9719060360b94@mail.gmail.com"
type="cite">
<pre wrap="">My next area of confusion is that I've looked at a bunch of data from
people such as Navteq, teleatlas, and a bunch of individual companies
databases, and it seems that every single one ships and stores their
data in lat/long. So what the heck? If the tools can't deal with
lat/long, why does everyone ship and store their data in lat/long?
Does everyone project this data before actually loading it into the
db? Help!?
</pre>
</blockquote>
No, I don't. I just load it in lat/lon. As a matter of fact, I think we
would better support lat/lon projections by trying it before
converting, fishing out problem area's and bugs and then enhancing the
software. So please, try in lat/lon and if it doesn't work, see if the
community can help you. I do understand that spherical vs cartesian
distances will be challenging, but perhaps the gdal/ogr and proj
projects will be able to support there.<br>
<blockquote
cite="mid:3fcf5fb70708101034j6d68600ay93e9719060360b94@mail.gmail.com"
type="cite">
<pre wrap="">
Now, it appears that Oracle in particular can do some functions with
lat/long directly (the distance calculation comes to mind), and I know
Postgis has some specialized distance functions for geodetic
coordinates, but I'm not sure if that extends to the whole function
set (i.e. can I do an Intersection of two polygons specified in
lat/long coordinates??). Why doesn't the OGC SFA spec and libraries
support all the functions with geodetic coordinates directly rather
than require projected coordinates?
</pre>
</blockquote>
Hit me, I don't know.<br>
<blockquote
cite="mid:3fcf5fb70708101034j6d68600ay93e9719060360b94@mail.gmail.com"
type="cite">
<pre wrap="">
Finally, how do the analysis and visualization tools that people put
on top of these databases deal with these questions? (e.g. MapInfo,
ArcView, etc.) They seem to want lat/long data as well, but if you
stored project coordinates in the database isn't there a problem??
</pre>
</blockquote>
MapInfo works fine, quantumGIS works fine, cartoweb works fine.
Mapserver works fine.<br>
<blockquote
cite="mid:3fcf5fb70708101034j6d68600ay93e9719060360b94@mail.gmail.com"
type="cite">
<pre wrap="">
HELP!
-Rick
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</pre>
</blockquote>
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