Hi Steve,
What you need to do is to project your lineString using some other
Coordinate Reference System (CRS). For example, here in NZ, I use the
NZGD2000/NZTM projection (probably using the wrong words here), which
represents everything in terms of metres from a particular point.
Below is a fragment of my code to read a WGS88 Shapefile, which represents
everything in degrees, and transform it into NZGD2000. Once the transform
is done, you can measure everything on your map in metres.
Frank
/**
* Load a WGS84 WGS84Shapefile, converting it to NZGD2000/NZTM, and
adding it to the result collection.
*
* @param result
* @param filepath
*/
public static void load(DefaultFeatureCollection result, String filepath)
{
log.debug("Loading WGS84 shapefile " + filepath);
SimpleFeatureSource featureSource;
try {
FileDataStore store = FileDataStoreFinder.getDataStore(new
File(filepath));
featureSource = store.getFeatureSource();
SimpleFeatureType schema = featureSource.getSchema();
CoordinateReferenceSystem fileCRS =
schema.getCoordinateReferenceSystem();
// Convert envelope limits to file crs for filter
MathTransform fromNZTM = CRS.findMathTransform(Global.internalCRS,
fileCRS, true);
Envelope limits = JTS.transform(Global.limits, fromNZTM);
Filter filter = CQL.toFilter("BBOX(the_geom, " + limits.getMinX() +
", " + limits.getMinY() + ", " + limits.getMaxX() + ", " + limits.getMaxY()
+ ")");
SimpleFeatureCollection coll = featureSource.getFeatures(filter);
makeNZTM(result, coll);
} catch (IOException ex) {
log.fatal("File not found: WGS84 shapefile " + filepath);
} catch (FactoryException | TransformException | CQLException ex) {
log.fatal(ex.getMessage(), ex);
}
}
/**
* Convert a Collection to NZGD2000/NZTM, and adding it to the result
collection Used only for loading Towns
*
* @param result
* @param coll
*/
private static void makeNZTM(DefaultFeatureCollection result,
SimpleFeatureCollection coll) {
MathTransform toNZTM = null;
SimpleFeatureType schema = coll.getSchema();
CoordinateReferenceSystem fileCRS =
schema.getCoordinateReferenceSystem();
try {
toNZTM = CRS.findMathTransform(fileCRS, Global.internalCRS, true);
} catch (FactoryException ex) {
log.fatal(ex.getMessage(), ex);
}
// This forces instantiation of each feature, as well as converting to
the NZTM
try (SimpleFeatureIterator i1 = coll.features()) {
while (i1.hasNext()) {
SimpleFeature f = i1.next();
Geometry geometry = ((Geometry) f.getDefaultGeometry()).union();
try {
Geometry geometry2 = JTS.transform(geometry, toNZTM);
Feature f2 = new Feature(f.getID(), (String)
f.getAttribute("name"));
f2.setDefaultGeometry(geometry2);
log.trace(f2.getID());
result.add(f2);
} catch (MismatchedDimensionException | TransformException ex) {
log.fatal(ex.getMessage(), ex);
}
}
i1.close();
}
}
On Mon, Jan 5, 2015 at 4:58 PM, Steve Mitchell <stevecmitch...@gmail.com>
wrote:
> Hopefully this is a simple question. Assuming that I've built a LineString
> like this:
>
> final GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
>
> final LineString lineString =
> geometryFactory.createLineString(coordinateArray);
>
> And now I want to generate mile or kilometer markers along that LineString.
> Is there a way to get lineString.getLength() to return, say miles, instead of
> degrees? I want to avoid having to loop through and use the
> GeodeticCalculator for every pair of points if there is a smarter way to do
> that with a LineString.
>
> I've stubbed out what I want to do:
>
> public Coordinate[] generateLapMarkers(final LineString lineString) {
> final SpatialIndex index = new STRtree();
> final LocationIndexedLine indexedPolyline = new
> LocationIndexedLine(lineString);
> final LinearLocation startLocation = indexedPolyline.getStartIndex();
> final Envelope search = lineString.getEnvelopeInternal();
> search.expandBy(1);
> index.insert(search, indexedPolyline);
> final double totalMiles = lineString.getLength(); // Some trick for
> getLength to return meters or miles.
>
> final List<Coordinate> laps = new
> ArrayList<Coordinate>((int)Math.floor(totalMiles)-1);
>
> // Didn't know how else to get LocationIndexedLine other than to search
> for itself.
> final List<LocationIndexedLine> locationIndexedLines =
> index.query(search);
> final LocationIndexedLine locationIndexedLine =
> locationIndexedLines.get(0);
> for (int d = 1; d < totalMiles; d++) {
> // Extract point by miles. Do we have to convert d back into degrees
> (d * magicToConvertDegreesIntoMetersRelativeToStartLocation)
> // or can the index be set-up to use meters instead of degrees.
> laps.add(locationIndexedLine.extractPoint(startLocation, d));
> }
> return laps.toArray(new Coordinate[laps.size()]);
> }
>
>
>
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