[postgis-users] about st_distance

[fsalas]

RE: [postgis-users] about st_distancethanks , Regina
  ----- Original Message ----- 
  From: Obe, Regina 
  To: PostGIS Users Discussion 
  Sent: Friday, October 03, 2008 7:49 PM
  Subject: RE: [postgis-users] about st_distance


  Francisco,

  ST_Distance (you can think of as min distance) returns the shortest distance between 2 geometries.  So between a point
  and a poly, if the point is in the poly the distance will be 0, it its outside it would be the distance between the closest point on the surface of the poly and the point. (there is actually another distance which no one asks about ST_MaxDistance - which is between the most distant point of a poly to a point - anyway I just mention it, but you wouldn't want to use it here).

  Your below query won't use indexes since ST_Distance doesn't use an index.  Use ST_Dwithin instead


  SELECT p.gid as id_parcela,tipo as tipo_Pozo
  FROM selepozo(1,1) po,parcelas p
  WHERE ST_DWithin(p.the_geom, po.the_geom, 1)

  http://postgis.refractions.net/documentation/manual-svn/ST_DWithin.html

  Hope that helps,
  Regina
  -----Original Message-----
  From: postgis-users-bounces at postgis.refractions.net on behalf of fsalas
  Sent: Fri 10/3/2008 7:01 AM
  To: postgis-users at postgis.refractions.net
  Subject: [postgis-users] about st_distance

  Hi,

  I need to know about obtain distance between polygon( parcels) and point

  I Use the next sentences

  SELECT p.gid as id_parcela,tipo as tipo_Pozo FROM selepozo(1,1) po,parcelas p WHERE ST_distance(p.the_geom, po.the_geom) < 1

  I have some questions

  This distance is between centroide of parcels to point or between border of parcels to point ?



  Best Regards,

  Francisco Salas


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Dpto de Sistemas Informáticos
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Este mensaje esta libre de virus. 
Revisado por Kaspersky Antivirus
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