I've tried multiply target projections, none come close. So I'm wondering if my source is set incorrectly.
The source data is a WGS84 geographic projection (I'm not sure why they call it a projection since its in decimal degrees lat/lons ie. -75.127811, 38.669757 ). My current question is whether I am setting the source correctly as EPSG:4326 or should it be a different value? Is there some way that I can interrogate the data to know what I should be setting the value to? I'm using the hsqldb import as the backing store for projections. Thanks again. PS. My latest run was using EPSG:26756 and the targetGeometry.getArea() returned 7.095211288232647E12 On Jul 8, 2010, at 6:01 PM, Ian Turton wrote: > On Thu, Jul 8, 2010 at 2:19 PM, Roark D Hennessy > <[email protected]> wrote: >> First I hope this is the right place to post. >> I want to get the square miles (or metres) from a given polygon (I used a >> well known area feature as test data). >> I took the example: >> >> import org.geotools.geometry.jts.JTS; >> import org.geotools.referencing.CRS; >> >> CoordinateReferenceSystem sourceCRS = CRS.decode("EPSG:4326"); >> CoordinateReferenceSystem targetCRS = CRS.decode("EPSG:23032"); >> >> MathTransform transform = CRS.findMathTransform(sourceCRS, targetCRS); >> Geometry targetGeometry = JTS.transform( sourceGeometry, transform); >> >> and >> The sourceGeometry is a polygon representing a state boundary. >> I did a targetGeometry.getArea(); >> The result is way off ( I tested against CT) 5.2836281456E9 for CT. it >> should be around 5400 sq miles give or take a couple hundred. One site has >> it at 5544 sq miles. >> I also did Nebraska and got 6.70387746...E10, should have been approximately >> 77,300 sq miles. >> questions: >> What is the return value units? > > The returned value is the units of your projection squared. So > according to units > You have: m^2 > You want: miles^2 > * 3.8610216e-07 > / 2589988.1 > > You need to calculate > 5.2836281456E9 * 3.8610216e-07 = 2040.02024 > > which looks off (but much closer) to your answer of 5400 (though the > census bureau says 4844 > http://quickfacts.census.gov/qfd/states/09000.html) > > >> Should I be using a different CRS for north america as target? > > EPSG:2163 is probably better. > > Ian > -- > Ian Turton > ------------------------------------------------------------------------------ This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
