Right, use 4269, that's a good NAD83-geographic-coordinates number. Import with shp2pgsql -s 4269 and go from there.
P On Mon, Dec 27, 2010 at 3:54 PM, Aren Cambre <a...@arencambre.com> wrote: > Brent and Paul, > Thank you for your help! > So here's my (new) dilemma--my PostGIS table doesn't appear to have a > projection specified, and I am not clear how to get to one. > I don't think it has a projection because this table's corresponding entry > in the geometry_columns table has -1 for the srid column. > This ShapeFile's PRJ file has this: > GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]] > I'm not seeing a clear match between this and any projection. > Some Google searching suggests this may be 4326, but I'm not sure about > this. And if I modify geometry_columns and import the PostGIS table into > QGis, I get this QGis error: > 1 cursor states lost. > SQL: CLOSE qgisf0 > Result: 7 (ERROR: current transaction is aborted, commands ignored until > end of transaction block > ) > If I revert that field back to -1, the error goes away on next import. > When I imported using shp2pgsql, I didn't use the -s switch. I presumed it > would catch the projection automatically. > I'm at a loss to know what to do next. I guess I need to figure out what the > true SRID of this data is before I can do any re-projections? > Aren > > On Mon, Dec 27, 2010 at 12:22 AM, Paul Ramsey <pram...@opengeo.org> wrote: >> >> You need to do your analysis in a projected coordinate system, not >> geographics. >> >> CREATE TABLE my_new_texas_roads AS >> SELECT ST_Transform(the_geom, 3081) as the_geom, other_attributes >> FROM texas_roads; >> >> EPSG:3081 should be a good coordinate system for working with your Texas >> data. >> >> http://spatialreference.org/ref/epsg/3081/ >> >> Not that the units are meters, so perform the appropriate linear >> transformations when looking for mile markers. >> >> Paul >> >> On Sun, Dec 26, 2010 at 4:35 PM, Aren Cambre <a...@arencambre.com> wrote: >> > I am trying to determine mile markers along Texas highways. My starting >> > point is the ShapeFile TxDOT Roadways 2010 >> > at http://www.tnris.state.tx.us/datadownload/download.jsp. I've used >> > shp2pgsql to get it into a PostGIS 1.52-enabled Postgres 9.01 database. >> > I naively thought I could just figure out the number of miles per unit >> > of >> > latitude and then traverse each roadway, one mile at a time, >> > using ST_Line_Interpolate_Point. However, predictably, the more >> > "longitudinal" a route, the more error it shows when I compare my >> > calculated >> > mile markers to what Google Maps shows. >> > Again, this is because I was using a consistent ratio of degrees to >> > miles, >> > so any route E-W component introduces errors. >> > So here's the question--does PostGIS allow any way to traverse a route a >> > set >> > distance at a time? Specifically, is there a way I can traverse a route >> > a >> > mile at a time and then record the points at the end of each mile? >> > I reviewed the functions available >> > >> > at http://postgis.refractions.net/documentation/manual-1.5/reference.html and >> > am not seeing anything clear. >> > In case it matters, the SHP's PRJ file says NAD83. >> > Aren Cambre >> > _______________________________________________ >> > postgis-users mailing list >> > postgis-users@postgis.refractions.net >> > http://postgis.refractions.net/mailman/listinfo/postgis-users >> > >> > >> _______________________________________________ >> postgis-users mailing list >> postgis-users@postgis.refractions.net >> http://postgis.refractions.net/mailman/listinfo/postgis-users > > > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users > > _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
