Thanks Andrea and Jody for your advice on this. I had to put this work
aside for a while and only just started looking at it again, but your
input was much appreciated.
I'm now working with some ZM shapefiles and have a related question
which I fear may require rather more work on my part. Reading these in
the standard way (getting a datastore using FileDataStoreFinder, using
that to get a FeatureSource then a FeatureCollection and iterating over
it) I get the Z ordinate if I call getCoordinates() on my geometries and
look at the z member of each Coordinate.
But what about the M ordinate? com.vividsolutions.jts.geom.Coordinate is
3D only, so even if the code that reads the shapefiles "knows" about the
M values (which it must do in a sense if only to skip over the relevant
bits of the file) it couldn't use this class to store them. The javadoc
for CoordinateSequence says: "There are some cases in which you might
want Geometries to store their points using something other than the JTS
Coordinate class ... one that supports extra attributes like M-values.
You can do this by implementing the CoordinateSequence and
CoordinateSequenceFactory interfaces."
They have an example of doing just that in
com.vividsolutions.jtsexample.geom.ExtendedCoordinate, but clearly some
extra work would be required to create a shapefile reader that could
make use of such 4D coordinates. Any pointers as to what code I should
use/ add to / modify to achieve this?
Thanks
Mark
On 16/07/10 09:47, Andrea Aime wrote:
> Mark Payne ha scritto:
>> So far I tried the following:
>>
>> featureSource = ds.getFeatureSource(FEATURE_TYPE_NAME);
>> DefaultQuery query = new DefaultQuery(DefaultQuery.ALL);
>> Hints hints = new Hints(Hints.COORDINATE_DIMENSION, new Integer(3),
>> Hints.FEATURE_2D,
>> Boolean.FALSE);
>> query.setHints(hints);
>> featureCollection = featureSource.getFeatures(query);
>>
>> That was the kind of thing you were meaning? I tried the hints that
>> seemed the most likely from the list that the Hints object provides.
>> Unfortunately it doesn't seem to make a difference, I just get
>> features with the X,Y components as before. Does anyone know if I'm
>> on the right track, or do I need to provide a different
>> CoordinateSequenceFactory as well?
>
> The code in the stable branches will pick up the 3rd dimension
> only if the crs had 3 axis:
>
> @Override
> public void encodeGeometryColumn(GeometryDescriptor gatt, int srid,
> StringBuffer sql) {
> CoordinateReferenceSystem crs =
> gatt.getCoordinateReferenceSystem();
> int dimensions = crs == null ? 2 : crs.getCoordinateSystem()
> .getDimension();
> sql.append("encode(");
> if (dimensions > 2) {
> sql.append("asEWKB(");
> encodeColumnName(gatt.getLocalName(), sql);
> } else {
> sql.append("asBinary(");
> sql.append("force_2d(");
> encodeColumnName(gatt.getLocalName(), sql);
> sql.append(")");
> }
> sql.append(",'XDR'),'base64')");
> }
>
> On trunk I've recently (two days ago?) made it use EWKB always,
> which means it should pull all the ordinates, but even
> that is not fully correct, as it does not respect the FORCE2D
> hint.
>
> Actually, the SQLDialect methods should be modified so that they
> get the hints otherwise it's not possible to implement things
> properly.
>
> I don't have time to look into this, do you? A patch on the
> code and an extension to the JDBC3DTest to check support for
> FORCE2D would be most welcomed
>
> Cheers
> Andrea
>
>
>
--
Mark Payne
Development Engineer
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