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<DIV dir=ltr align=left><SPAN class=281142821-13072009><FONT color=#0000ff
size=2 face=Arial>Is T as true timestamp in MM/SQL specs. Wouldn't we
be breaking our compliance. Not that we aren't in other ways --
but.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=281142821-13072009><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=281142821-13072009><FONT color=#0000ff
size=2 face=Arial>I suppose its not possible to have people decide what kind of
index to build -- like some parameter to GIST or whatever. That way people
who don't want to pay the 10% disk penalty won't have to.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=281142821-13072009><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=281142821-13072009><FONT color=#0000ff
size=2 face=Arial>Thanks,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=281142821-13072009><FONT color=#0000ff
size=2 face=Arial>Regina</FONT></SPAN></DIV><BR>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
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<FONT size=2 face=Tahoma><B>From:</B>
postgis-devel-bounces@postgis.refractions.net
[mailto:postgis-devel-bounces@postgis.refractions.net] <B>On Behalf Of </B>David
William Bitner<BR><B>Sent:</B> Monday, July 13, 2009 5:19 PM<BR><B>To:</B>
PostGIS Development Discussion<BR><B>Subject:</B> Re: [postgis-devel] Multi-D
Indexing and Serialized Form<BR></FONT><BR></DIV>
<DIV></DIV>If we're opening up the whole ball of wax and looking at the
potential things that could go into a liblwgeom2 serialized form, would there be
any possibilities to have a T dimension that was an actual timestamp (as opposed
to the typical use of an offset from a time)???<BR><BR>
<DIV class=gmail_quote>On Mon, Jul 13, 2009 at 4:04 PM, Paul Ramsey <SPAN
dir=ltr><<A
href="mailto:pramsey@opengeo.org">pramsey@opengeo.org</A>></SPAN> wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: rgb(204,204,204) 1px solid; MARGIN: 0pt 0pt 0pt 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>For my "geography" work, I am trying to ensure that what I
do either<BR>uses existing liblwgeom hooks, or creates new things that
liblwgeom2<BR>could use. I'll be doing indexing as a 3-space index, and that
works<BR>OK for geography, things are static:<BR><BR>bbox dims =
3<BR>coordinate dims = 2<BR><BR>However, for geometry, we were thinking about
adding multidimensional<BR>indexing. Right now we have a situation like this
for geometry:<BR><BR>bbox dims = 2<BR>coordinate dims = 2/3/4<BR><BR>No
problem, because we only calculate a 2d box, no matter what
our<BR>dimensionality. But when we add the possibility of
multi-dimensional<BR>indexes, we get in a bind. How many dimensions of bbox
should we<BR>calculate? We need enough to support the index, but we don't know
what<BR>the dimensionality of the index using the bbox will be. That leaves
us<BR>forced to calculate the full multi-dimensional bbox even if we
only<BR>want a 2-d index. We also could end up with some interesting
problems,<BR>for example, returning results from a 4d index given a 2d query
bbox.<BR><BR>The straightest line solution, IMO, is to just create a bbox
with<BR>enough dimensionality to handle the coordinates. So we'll end up
with<BR><BR>coordinate dims = 2 => bbox dims = 2<BR>coordinate dims = 3
=> bbox dims = 3<BR>coordinate dims = 4 => bbox dims = 4<BR><BR>For
2-vertex 3d points that you only want a 2d index on (the worst<BR>case, since
we don't put boxes on points), that implies a storage<BR>overhead of about
10%.<BR><BR>P.<BR>_______________________________________________<BR>postgis-devel
mailing list<BR><A
href="mailto:postgis-devel@postgis.refractions.net">postgis-devel@postgis.refractions.net</A><BR><A
href="http://postgis.refractions.net/mailman/listinfo/postgis-devel"
target=_blank>http://postgis.refractions.net/mailman/listinfo/postgis-devel</A><BR></BLOCKQUOTE></DIV><BR><BR
clear=all><BR>-- <BR>************************************<BR>David William
Bitner<BR></BODY></HTML>