<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
I can't figure out how to extract/compute the BBOX from an SQLite BLOB,
without parsing the geometry.<br>
I belive that it is faster to read the BBOX values rather than a
potentially large BLOB field.<br>
<br>
I agree that it would use some space to add the columns, but adding the
columns would enable a fast filtering of unused features.<br>
As for the 4 times index, one could merely add index for the x values,
and then use sequential filtering for the y values. <br>
<br>
Is your internal spatial index algorithm absolutely without benefit
from added BBOX columns?<br>
<br>
<pre class="moz-signature" cols="72">Regards, Kenneth, GEOGRAF A/S
</pre>
<br>
<br>
Traian Stanev skrev:
<blockquote
cite="mid:D20FC5C02CA4AB41891CFE76D91C57A925300D69D2@ADSK-NAMSG-02.MGDADSK.autodesk.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html; ">
<meta name="Generator" content="Microsoft Word 12 (filtered medium)">
<!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]-->
<style>
<!--
/* Font Definitions */
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";
color:black;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0in;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";
color:black;}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;
color:black;}
span.EmailStyle19
{mso-style-type:personal;
font-family:"Calibri","sans-serif";
color:windowtext;}
span.EmailStyle20
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page Section1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.Section1
{page:Section1;}
-->
</style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
<div class="Section1">
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">It’s a
waste of space to
store BBOX. It would cost at least 32 bytes per feature, not counting
the
indexes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Also, you
can easily compute the
bounding box and add those 4 columns very quickly when you need them,
given
that SQLite is pretty fast to read from. Indexing on the 4 BBOX columns
would
make spatial queries have to compute the intersection of the results of
4 tree
searches. SQLite is fast, but it’s not *<b>that</b>* fast.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Anyway,
the nice thing about
this format is that you can create the BBOX columns anyway, and use
them. The
FDO provider will not be using it though, for performance reasons.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Traian<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<div
style="border-style: none none none solid; border-color: -moz-use-text-color -moz-use-text-color -moz-use-text-color blue; border-width: medium medium medium 1.5pt; padding: 0in 0in 0in 4pt;">
<div>
<div
style="border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; border-width: 1pt medium medium; padding: 3pt 0in 0in;">
<p class="MsoNormal"><b><span
style="font-size: 10pt; font-family: "Tahoma","sans-serif"; color: windowtext;">From:</span></b><span
style="font-size: 10pt; font-family: "Tahoma","sans-serif"; color: windowtext;">
<a class="moz-txt-link-abbreviated" href="mailto:fdo-internals-bounces@lists.osgeo.org">fdo-internals-bounces@lists.osgeo.org</a>
[<a class="moz-txt-link-freetext" href="mailto:fdo-internals-bounces@lists.osgeo.org">mailto:fdo-internals-bounces@lists.osgeo.org</a>] <b>On Behalf Of </b>Kenneth,
GEOGRAF A/S<br>
<b>Sent:</b> Tuesday, March 25, 2008 7:12 AM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> Re: [fdo-internals] FDO RFC 16 - FDO Provider for
SQLite<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I just re-read the RFC.<br>
<br>
What are your reasons for not storing BBOX releated data in the data
table?<span style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><br>
<br>
I would suggest adding four columns, like minx, maxx, miny, max
(perhaps name
them via. the geometry_columns table?).<br>
With that approach, and index on the pairs would move the BBOX query
load/optimization into the DBMS.<br>
BBOX queries are simple, and does not require reading the actual column
data.<br>
<br>
Your extended spatial index algorithm might read these values to
produce the
search tree.<br>
<br>
Another suggestion, would be to store the search tree in a blob column.<br>
That would enable a much faster load of data.<br>
<br>
To avoid the requirement that all data updaters know the algorithm, it
might be
legal to just clear the BLOB data on updates.<br>
<br>
I wrote a short paper on a similar mechanism some time ago, with a
friend:<br>
<a moz-do-not-send="true"
href="http://www.hexad.dk/opensource/spatialdbms.pdf">http://www.hexad.dk/opensource/spatialdbms.pdf</a><br>
<br>
<br>
<br>
<o:p></o:p></p>
<pre>Regards, Kenneth, GEOGRAF A/S<o:p></o:p></pre>
<p class="MsoNormal"><br>
<br>
Traian Stanev skrev: <o:p></o:p></p>
<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I just posted FDO RFC #16. Fresh off the virtual
presses
(printed on 100% recycled electrons, for you green-minded folks):<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"><a moz-do-not-send="true"
href="http://trac.osgeo.org/fdo/wiki/FDORfc16">http://trac.osgeo.org/fdo/wiki/FDORfc16</a><o:p></o:p></p>
<p class="MsoNormal"> <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">Traian<o:p></o:p></p>
<pre><o:p> </o:p></pre>
<pre style="text-align: center;">
<hr align="center" size="4" width="90%">
</pre>
<pre><o:p> </o:p></pre>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>fdo-internals mailing list<o:p></o:p></pre>
<pre><a moz-do-not-send="true"
href="mailto:fdo-internals@lists.osgeo.org">fdo-internals@lists.osgeo.org</a><o:p></o:p></pre>
<pre><a moz-do-not-send="true"
href="http://lists.osgeo.org/mailman/listinfo/fdo-internals">http://lists.osgeo.org/mailman/listinfo/fdo-internals</a><o:p></o:p></pre>
<pre> <o:p></o:p></pre>
</div>
</div>
<pre wrap="">
<hr size="4" width="90%">
_______________________________________________
fdo-internals mailing list
<a class="moz-txt-link-abbreviated" href="mailto:fdo-internals@lists.osgeo.org">fdo-internals@lists.osgeo.org</a>
<a class="moz-txt-link-freetext" href="http://lists.osgeo.org/mailman/listinfo/fdo-internals">http://lists.osgeo.org/mailman/listinfo/fdo-internals</a>
</pre>
</blockquote>
</body>
</html>