Hi Nuno,
Quick question since it lines up with some of what Jody has been
discussing...
Are you expecting to support more than one measure (i.e., multiple M's?)
or just one? (I'm biased since I'd only need one measure. Jody points
to the other cases where users have a number of measures.)
Cheers,
Jim
On 07/31/2018 01:19 PM, Nuno Oliveira wrote:
Hi Andrea,
please see my answers bellow :)
On 07/31/2018 01:53 PM, Andrea Aime wrote:
I believe it would be nice/useful to have information about the M at
the GeometryDescriptor level,
like done in this commit for the dimensions:
https://github.com/geotools/geotools/commit/a9c4b52c0404ec0357d0006ce8900c209875ec9a
but during a discussion you reported that the info is not always
available and/or we might have
a mix of mesured and non measured geometries, could you elaborate?
Yes the goal is to have the information about the available
measurements in the
user data of the geometry descriptor, similar to the dimension
information [1],
is this aligned with what you were thinking ?
Data stores like PostGIS and shapefiles allow us to be explicit about
the existence
of a measurement, e.g. using geometry types like PointM or
LineStringM, so we
can infer the number of available measurements by looking at the
meta-data,
but that may not be the case for all the other supported data stores ...
For the cases where is not possible to infer the number of
measurements automatically
we will need to allow the user to provide it explicitly when
configuring the layer. Note that
this may also be needed for use cases where the user was not explicit
about the
geometry type.
For the moment I'm focusing \ supporting only the use cases where we
can infer it automatically.
[1]
https://github.com/geotools/geotools/blob/master/modules/library/jdbc/src/main/java/org/geotools/jdbc/JDBCFeatureSource.java#L330
On Tue, Jul 31, 2018 at 2:11 PM Nuno Oliveira
<[email protected]
<mailto:[email protected]>> wrote:
I ended up having CoordianteSequence.getDimension() as
described in the
conversation above, and
CoordianteSequence.getMeasures() being the number of measures
(so if we have
XYZM dimension is 4 and measures is 1.
This would be a new method in a GeoTools "trait" interface that only
some CoordinateSequences would
implement?
Yes, so basically when reading the geometry from the data source (e.g.
PostGIS [2]) we will store the
information about the available measurements in the geometry user
data, then we will use the new
getMeasures() utility method in the CoordianteSequence trait to get
the information when needed, e.g.
when encoding the geometry to GML 3.2 [3].
[2]
https://github.com/geotools/geotools/blob/master/modules/plugin/jdbc/jdbc-postgis/src/main/java/org/geotools/data/postgis/WKBReader.java#L181-L211
[3]
https://github.com/geotools/geotools/blob/master/modules/extension/xsd/xsd-gml2/src/main/java/org/geotools/gml2/simple/GMLWriter.java#L287-L301
1. correctly read geometries with measurements from data sources
2. correctly encode the measurements in the output formats
3. correctly handling measurements when doing certain
operations, e.g.
re-projections
Have a look here:
https://github.com/geotools/geotools/blob/9fbd02a320fa19d563972808d226a0a0445a5b13/modules/library/api/src/main/java/org/geotools/geometry/jts/DefaultCoordinateSequenceTransformer.java#L61
Ah yes the re-projections, I hope this class concentrates must of the
code used to re-project the coordinates sequences ...
The following issue in GeoServer as an interesting discussion
about this:
https://osgeo-org.atlassian.net/browse/GEOS-8858
Yep, some output formats are allergic to M and we'd have to decide if
to return it as a vendor extension (much like the way
we handle 2.5D data declaring a 2D CRS) and others allow loopholes
but again not all clients might understand.
Ideally that configuration should be per layer basis, i.e. if M are
available select all the output formats that should output it.
My main doubt is how to make that information reach the for example
the GML encoder ... a thread local ? Alternatives here
are welcome :)
Cheers
Andrea
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