You should be able to supply a custom coordinate sequence factory as a hint;
but some patches may be required to have shapefile actually pick up and respect
your hint (you are the first person trying this out; so even though we have
planned for these ideas; the actual work waits until someone real has data to
work with).
Jody
On 25/08/2010, at 2:43 AM, Mark Payne wrote:
> 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
>
> Tel: +44 (0) 131 447 4200 Address: SeeByte Ltd.
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