Hi, I have a large set of oceanic point data that I need to test to identify all points that are within a certain distance of land. I initially tried doing the most obvious thing I could think of - buffer land polygons and test points for intersection, but this is taking too long for the full dataset and is giving me strange "terminating connection due to administrator command" errors. I imagine that there is something in my initial strategy that doesn't scale well, but it is hard for me to identify what is the best strategy. Hopefully someone already knows the answer and can give me a hand.
Here are some concrete questions that I hope someone can help me with: 1) How exactly are indexes used for point data? AS BBox doesn't make much sense (at least to me), I imagine that this somehow groups identical points so that operations only have to be done once for each distinct point. Is this the case? 2) I initially made a function to test for proximity to land: CREATE OR REPLACE FUNCTION near_land(geo geometry) RETURNS boolean AS $BODY$ SELECT bool_or( ST_Intersects($1,wkb_geometry_5km_buf) ) FROM gshhs_h_l1; $BODY$ LANGUAGE 'sql' STABLE; This works fast for small amounts of data, but I have a feeling that this prohibits using indexes for the full dataset and therefore could be causing much of my slowness. Is this so? 3) Would it be best to ST_Union all my polygons before making the comparison, knowing that the polygons don't overlap? Or is this no different than just doing the intersect and then using bool_or? 4) Would using long transaction support help me avoid the "administrator command" errors? I don't really know what long transaction support does, but my transaction certainly is long... Thanks for the help. Cheers, David -- ********************************** David M. Kaplan Charge de Recherche 1 Institut de Recherche pour le Developpement Centre de Recherche Halieutique Mediterraneenne et Tropicale av. Jean Monnet B.P. 171 34203 Sete cedex France Phone: +33 (0)4 99 57 32 27 Fax: +33 (0)4 99 57 32 95 http://www.ur097.ird.fr/team/dkaplan/index.html http://www.amped.ird.fr/ ********************************** _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
