Hey all,
I think I am misunderstanding something regarding the projections. If
someone could help me out here, I would really appreciate it. I had
initially posted to the geo-server mailing list, but thought the more
appropriate one was this one.
We have in our code functions to convert a lat/long to the Google
projection, and back. It is a bunch of straight math transforms on
points, and I wanted to make it a little more generic to use the
Geometry class. I started up a test to check that I could go from one
to the other (note: I am not certain what the actual expected values
from the Google projection are right now, so bear with me) and back, but
I obviously have something wrong. Can someone look over what I have
below and let me know where my confusion is? I have tried changing both
the source and target projections in the transform, as well as using the
same source and target projections but inverting the transform. Here is
my code:
package ca.intelliware.services;
import junit.framework.TestCase;
import org.geotools.geometry.jts.JTS;
import org.geotools.referencing.CRS;
import org.geotools.referencing.factory.AbstractAuthorityFactory;
import org.geotools.referencing.factory.epsg.PostgreDataSource;
import org.opengis.referencing.FactoryException;
import org.opengis.referencing.crs.CoordinateReferenceSystem;
import org.opengis.referencing.operation.MathTransform;
import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.Point;
import com.vividsolutions.jts.geom.PrecisionModel;
public class TestProjectAndProjectBack extends TestCase {
public static final String EPSG_4326 = "EPSG:4326";
public static final String EPSG_900913 = "PROJCS[\"WGS84 /
Google Mercator\", GEOGCS[\"WGS 84\", DATUM[\"World Geodetic System
1984\", SPHEROID[\"WGS 84\", 6378137.0, 298.257223563,
AUTHORITY[\"EPSG\",\"7030\"]], AUTHORITY[\"EPSG\",\"6326\"]],
PRIMEM[\"Greenwich\", 0.0, AUTHORITY[\"EPSG\",\"8901\"]],
UNIT[\"degree\", 0.017453292519943295], AXIS[\"Geodetic latitude\",
NORTH], AXIS[\"Geodetic longitude\", EAST],
AUTHORITY[\"EPSG\",\"4326\"]], PROJECTION[\"Mercator_1SP\"],
PARAMETER[\"semi_minor\", 6378137.0], PARAMETER[\"latitude_of_origin\",
0.0], PARAMETER[\"central_meridian\", 0.0], PARAMETER[\"scale_factor\",
1.0], PARAMETER[\"false_easting\", 0.0], PARAMETER[\"false_northing\",
0.0], UNIT[\"m\", 1.0], AXIS[\"Easting\", EAST], AXIS[\"Northing\",
NORTH], AUTHORITY[\"EPSG\",\"900913\"]]";
@SuppressWarnings("deprecation")
public void
testConvertFromDecimalDegreesToGoogleAndBackGivesSameValuesUsingGeometri
es() {
Geometry original = new Point(new Coordinate(new
Double("-81.123456"), new Double("45.123456")),new
PrecisionModel(PrecisionModel.FLOATING_SINGLE), 4326);
Geometry converted =
fromDecimalDegreesToGoogleTransverseMercator(original);
assertSignificantlyDifferent(original,
converted);
Geometry convertedBack =
fromGoogleTransverseMercatorToDecimalDegrees(original);
assertNotSignificantlyDifferent(original,
convertedBack);
}
private void assertSignificantlyDifferent(Geometry geo1,
Geometry geo2) {
assertTrue(!geo1.equals(geo2));
}
private void assertNotSignificantlyDifferent(Geometry geo1,
Geometry geo2) {
assertTrue(geo1.equals(geo2));
}
private Geometry
fromDecimalDegreesToGoogleTransverseMercator(Geometry geom) {
try {
MathTransform math =
CRS.findMathTransform(getEpsg4326CRS(), getEpsg900913CRS());
return JTS.transform(geom, math);
} catch (Exception e) {
throw new
IllegalStateException("Unable to convert geometry:\n" + e.getMessage());
}
}
public Geometry
fromGoogleTransverseMercatorToDecimalDegrees(Geometry geom) {
try {
MathTransform math =
CRS.findMathTransform(getEpsg900913CRS(), getEpsg4326CRS());
return JTS.transform(geom, math);
// MathTransform math =
CRS.findMathTransform(getEpsg4326CRS(), getEpsg900913CRS());
// return JTS.transform(geom,
math.inverse());
} catch (Exception e) {
throw new
IllegalStateException("Unable to convert geometry:\n" + e.getMessage());
}
}
public CoordinateReferenceSystem getEpsg4326CRS() {
try {
PostgreDataSource postgreDataSource
= SpringLocator.getEPSGPostgreDataSource();
AbstractAuthorityFactory
abstractAuthorityFactory = postgreDataSource.createFactory(null);
return
abstractAuthorityFactory.createCoordinateReferenceSystem(EPSG_4326);
} catch (Exception e) {
throw new RuntimeException("FATAL:
Unable to create a CRS for " + EPSG_4326);
}
}
public CoordinateReferenceSystem getEpsg900913CRS() {
try {
return CRS.parseWKT(EPSG_900913);
} catch (FactoryException e) {
throw new RuntimeException("FATAL:
Unable to create a CRS for " + EPSG_900913);
}
}
}
Thanks,
-mike
________________________________
"I don't think that the right time to tell a dog not to pee on the
carpet is semiannually."
House MD on performance reviews
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