With geotools would it be possible that generating a polygon from a line (coords[]) in a defined distance? E.g. (100,100), (101,100), (102,100) with distance 1km. So from each point it generates a circle and becomes sth. like:
-------------- before
(========) after
Or I have to firstly convert GPS coordinates into orthogonal coordinates in km, and then generating a polygon using Trigonometric functions, and finally, convert it back into GPS?
At it's simplest you simply need to call the buffer(distance) method on the underlying JTS geometry. The tricky bit is handling the reprojection to and from a projection which is in meters (so you can specify your buffer in meters or kilometers).
public SimpleFeature bufferFeature(SimpleFeature feature,
Measure<Double, Length> distance) {
// extract the geometry
GeometryAttribute gProp = feature.getDefaultGeometryProperty();
CoordinateReferenceSystem origCRS = gProp.getDescriptor()
.getCoordinateReferenceSystem();
Geometry geom = (Geometry) feature.getDefaultGeometry();
Geometry pGeom = geom;
MathTransform toTransform,fromTransform = null;
// reproject the geometry to a local projection
if (!(origCRS instanceof ProjectedCRS)) {
Point c = geom.getCentroid();
double x = c.getCoordinate().x;
double y = c.getCoordinate().y;
String code = "AUTO:42001," + x + "," + y;
// System.out.println(code);
CoordinateReferenceSystem auto;
try {
auto = CRS.decode(code);
toTransform = CRS.findMathTransform(
DefaultGeographicCRS.WGS84, auto);
fromTransform = CRS.findMathTransform(auto,
DefaultGeographicCRS.WGS84);
pGeom = JTS.transform(geom, toTransform);
} catch (MismatchedDimensionException | TransformException
| FactoryException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
// buffer
Geometry out = buffer(pGeom, distance.doubleValue(SI.METER));
Geometry retGeom = out;
// reproject the geometry to the original projection
if (!(origCRS instanceof ProjectedCRS)) {
try {
retGeom = JTS.transform(out, fromTransform);
} catch (MismatchedDimensionException | TransformException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
// return a new feature containing the geom
SimpleFeatureType schema = feature.getFeatureType();
SimpleFeatureTypeBuilder ftBuilder = new SimpleFeatureTypeBuilder();
ftBuilder.setCRS(origCRS);
//ftBuilder.setDefaultGeometry("buffer");
ftBuilder.addAll(schema.getAttributeDescriptors());
ftBuilder.setName(schema.getName());
SimpleFeatureType nSchema = ftBuilder.buildFeatureType();
SimpleFeatureBuilder builder = new SimpleFeatureBuilder(nSchema);
List<Object> atts = feature.getAttributes();
for(int i=0;i<atts.size();i++) {
if(atts.get(i) instanceof Geometry) {
atts.set(i, retGeom);
}
}
SimpleFeature nFeature = builder.buildFeature(null, atts.toArray() );
return nFeature;
}
The full code is at https://gist.github.com/ianturton/9a7cfee378e7072ec3cd which shows how to handle the whole thing.
Yes, this would be definitely possible to do so with out converting coordinates. But if you are looking certain properties, such as rectilinear, then coordinate conversion might be necessary.
