<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi John,<div><br></div><div>Regarding snapping points to lines, postgis does not have a built-in function to do that, but this nice post gives you a good guide on how to accomplish it: <a href="http://blog.cleverelephant.ca/2008/04/snapping-points-in-postgis.html">http://blog.cleverelephant.ca/2008/04/snapping-points-in-postgis.html</a></div><div><br></div><div>Regarding how to do a 'Dissolve' in postgis, I assume you are referring to the Dissolve command equivalent in ArcGIS where polygons with shared boundaries are merged or otherwise turned into multipolygons wen they share a common attribute? In postgis this is done by the combination of the ST_Union() function on the geometry and a Group By on an attribute. Something like:</div><div><br></div><div>SELECT ST_Union(the_geom) INTO dissolved_polygons FROM your_table GROUP BY your_attribute;</div><div><br></div><div>If you want to run that step with a faster function then read the wiki post here to learn how to use the new/proposed cascaded union function:</div><div><br></div><div><a href="http://postgis.refractions.net/support/wiki/index.php?upgis_cascadeunion">http://postgis.refractions.net/support/wiki/index.php?upgis_cascadeunion</a></div><div><br></div><div>Dane</div><div><br></div><div><br><div><div>On Oct 6, 2008, at 1:35 PM, John Zhang wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr">Hi there,<br><br>I am writing to check how to perform SNAP and DISSOLVE function by PostGIS. <br><br>I have a point dataset table and a MultipleLineString dataset table. I need to snap all the points in the dataset to the Line Strings when the distance is within 100 meters. <br> <br>I also need union some polygon features and dissolve the polygons within a polygon. <br><br>Any inputs would be appreciated.<br clear="all"><br>-- <br>Sincerely,<br><br><br>John Zhang, M.Sc., B.Sc., A.Dipl.T.<br>email: <a href="mailto:JohnZhang06@gmail.com">JohnZhang06@gmail.com</a><br> Phone: 604-998-1874<br><br>URL: <a href="http://ca.geocities.com/john_z04/JOHN_ZHANG_GIS.html">http://ca.geocities.com/john_z04/JOHN_ZHANG_GIS.html</a><br> </div> _______________________________________________<br>postgis-users mailing list<br><a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>http://postgis.refractions.net/mailman/listinfo/postgis-users<br></blockquote></div><br></div></body></html>