<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">Hi Alex,</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">I’d say in general it’s a pretty huge drawback, and most users go “yeah, KNN, awsome! oh, wait, really? that’s all it does?”</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">Almost any example with non-point data gives the wrong answer to “give me the N nearest” when using the bounding boxes instead of the actual objects. I can put together some test cases if you like, but any road data set will display it, “show me the nearest roads to this point”. Inevitably some long highway segment with a huge box that’s otherwise not anywhere near the test point shows up in the list of nearest things.</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">P.</div> <div id="bloop_sign_1389966739697650944" class="bloop_sign"><div><br></div><span style="font-family:helvetica,arial;font-size:13px"></span>-- <br>Paul Ramsey<br>http://cleverelephant.ca<div>http://postgis.net</div></div> <br><p style="color:#A0A0A8;">On January 17, 2014 at 8:51:41 AM, Alexander Korotkov (<a href="mailto://aekorotkov@gmail.com">aekorotkov@gmail.com</a>) wrote:</p> <blockquote type="cite" class="clean_bq"><span><div><div>
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<div><span style="font-family:arial,sans-serif;font-size:13px">Hi,
PostGIS developers!</span></div>
<div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div>
<div><span style="font-family:arial,sans-serif;font-size:13px">Currently, PostGIS
supports knn-gist with <-> and <#> operators which are
distance to centroid and MBR, but not exact distance to geometrical
object, because of knn-gist limitation. However, it's not so
fundamental limitation, in principle index distance could be
rechecked from heap providing exact knn.</span></div>
<div><span style="font-family:arial,sans-serif;font-size:13px">Do
you know PostGIS users lacking of such exact knn? If so, could you
give some example where <-> and <#> operators are
really insufficient?</span></div>
<div><br></div>
<span style="font-family:arial,sans-serif;font-size:13px">------</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">With best
regards,</span><br style="font-family:arial,sans-serif;font-size:13px">
<span style="font-family:arial,sans-serif;font-size:13px">Alexander
Korotkov.</span><br></div>
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