Hi Peter, It sounds like you are wanting to tile your polygons. Not really ideal, as each polygon is rendered via tiles, so you need to render them without borders to hide the tiles, then often plot the border as well, which still has all the vertices. Lots more work.
You might look at simplifying your polygons to reduce the number of vertices in each. If you manage your data topologically, this process will work better at retaining shared boundaries. If you can use Google to provide vector zoom layers, then as you zoom in you can get less & less simplified versions... just like pyramid'ed rasters. Zoomed out you can't see so don't provide the unnecessary detail. I don't use Google myself, the licence terms are too restrictive for much of the data I work with, so can't say how well this works in a Google environment. Brent Wood --- On Fri, 3/4/11, Peter N. Schweitzer <pschweit...@usgs.gov> wrote: From: Peter N. Schweitzer <pschweit...@usgs.gov> Subject: [postgis-users] A way to split polygons? To: "PostGIS Users Discussion" <postgis-users@postgis.refractions.net> Date: Friday, March 4, 2011, 9:44 AM At http://tin.er.usgs.gov/geology/state/ and pages below it, I provide geologic map units for US states in KML for use within Google Earth. These are stored in PostgreSQL (9.0.2) with PostGIS (1.5.2). My problem is that many of the larger geologic units are represented as polygons that have a large number of vertices, often with many interior rings. Google Earth doesn't want to display polygons that have 100,000 vertices (I think the actual limit is lower, but I don't know what it is.) So my geologic maps have large irregular holes in them when viewed in Google Earth. Is there a way, using PostGIS functions, to split these polygons so that the resulting polygons have fewer vertices and thus would appear as expected in Google Earth? It seems to me one possibility would be to intersect these large polygons with Box2D's whose vertical dimensions were, say, one or two degrees. But I don't yet see how to carry this operation out. Can anyone offer suggestions as to how this might be done? Here are some of the characteristics of the data. The principal table containing the polygons is named geol_poly; the field unit_link is a relational key to other, more interesting data, and the_geom comes through shp2pgsql. select unit_link,ST_NPoints(the_geom) npt,ST_NumGeometries(the_geom) ng, ST_NumInteriorRings(the_geom) ni from geol_poly order by npt desc; unit_link | npt | ng | ni -----------------+--------+----+------ FLwater;0 | 451759 | 1 | 8945 PAPAa;6 | 319192 | 1 | 1235 PAPAcg;6 | 216653 | 1 | 925 ALwater;0 | 205251 | 1 | 108 OHPAc;0 | 201310 | 1 | 842 OHPAm;0 | 200763 | 1 | 895 OHPAap;0 | 196422 | 1 | 1207 MNOl;0 | 188753 | 1 | 107 MNCu;0 | 165061 | 1 | 86 TNObh;6 | 152421 | 1 | 825 PAPAp;6 | 144889 | 1 | 324 MOOjc;0 | 144721 | 1 | 144 MOMk;0 | 128731 | 1 | 290 WVPAk;0 | 128402 | 1 | 934 TXKed;0 | 124666 | 1 | 720 TNMfp;10 | 122021 | 1 | 117 OHMlc;0 | 116993 | 1 | 731 TNMfp;10 | 113034 | 1 | 406 MOOr;0 | 109195 | 1 | 136 PAPAm;6 | 105906 | 1 | 395 PAPAcc;6 | 105798 | 1 | 447 WVPAm;0 | 99944 | 1 | 474 CAQ;0 | 97086 | 1 | 455 WVPAc;0 | 94277 | 1 | 455 MNOm;0 | 93054 | 1 | 53 PAPPAw;0 | 89974 | 1 | 218 TNOca;6 | 89292 | 1 | 564 WVPAa;0 | 89182 | 1 | 504 MOOr;0 | 87103 | 1 | 171 MOOg;0 | 85660 | 1 | 277 Peter -- Peter N. Schweitzer (MS 954, U.S. Geological Survey, Reston, VA 20192) (703) 648-6533 FAX: (703) 648-6252 email: pschweit...@usgs.gov <http://geology.usgs.gov/peter/> _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
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