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/>
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