Just wanted to report to the list that I seem to have successfully applied the tiling idea to these geologic map units, by creating a separate table containing only those polygons where ST_NPoints(the_geom) > 10000, a table containing tiles that are 1/7th of a degree square, and a third table containing the intersection of the complex polygons with the tiles. By marking, in the original polygon table, those polygons for which I have tiled versions, I am now able to generate KML that is simple enough for Google Earth to display.
I'm happy about this because this is a problem that has been following me for several years now--every once in a while I would receive email from a user inquiring about polygons that weren't displaying properly in Google Earth. A proper understanding and application of PostGIS's ST_Intersects and ST_Intersection functions, coupled with some bookkeeping, has made this solution possible. So for any who are interested, the end result is the collection of KML files linked from http://tin.er.usgs.gov/geology/state/kml/ or from individual pages describing the state geologic map compilation, from http://tin.er.usgs.gov/geology/state/ There remains to be explored the worthwhile suggestion of generating lower-resolution versions of these data for use with KML regions, to speed the display within Google Earth. For now, however, these data seem (to me) to render readily enough. Thanks to those from this list who offered suggestions towards solving this problem. Peter On 03/03/2011 03:44 PM, Peter N. Schweitzer wrote:
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
