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Writing and reading WKB loses M dimension #733

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kaiwinter opened this issue May 26, 2021 · 2 comments · May be fixed by #1092
Open

Writing and reading WKB loses M dimension #733

kaiwinter opened this issue May 26, 2021 · 2 comments · May be fixed by #1092

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@kaiwinter
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When using WKBWriter to write a Geometry which has XYM coordinates and afterwards using WKBReader for reading the result. The Geometry has XYZ coordinates instead of XYM coordinates.

Here is small example:

    String wkt = "MULTILINESTRING M((1 1 1, 2 2 2))";
    WKTReader wktReader = new WKTReader();
    Geometry geometryBefore = wktReader.read(wkt);

    WKBWriter wkbWriter = new WKBWriter(3);
    byte[] write = wkbWriter.write(geometryBefore);

    WKBReader wkbReader = new WKBReader();
    Geometry geometryAfter = wkbReader.read(write);

    System.out.println(Arrays.asList(geometryBefore.getCoordinates()));
    System.out.println(Arrays.asList(geometryAfter.getCoordinates()));

When running this you get the following output:

[(1.0, 1.0 m=1.0), (2.0, 2.0 m=2.0)]
[(1.0, 1.0, 1.0), (2.0, 2.0, 2.0)]

The geometryBefore has XYM coordinates. The geometryAfter has XYZ coordinates.
In WKBReader.readGeometry are two variables evaluated hasZ and hasM. In the above example hasZ is true and hasM is false. I think this is because WKBWriter.writeGeometryType always writes 0x80000000 regardless of the coordinate type. Debugging WKBReader.readGeometry makes me think 0x40000000 should be used for M coordinates in WKBWriter.writeGeometryType.

What do you think? Can this be improved or did I just misunderstood how this should work.
@kaiwinter kaiwinter changed the title Writing and reading WKB looses M dimension Writing and reading WKB loses M dimension May 26, 2021
@jnh5y
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jnh5y commented May 26, 2021

I think you've identified a bug here. Any interest in working on it?

The Contributing guide has some info about that here: https://github.com/locationtech/jts/blob/master/CONTRIBUTING.md

@kaiwinter
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Yes sure. Currently I'm using a workaround with a GeometryFactory but I would love to get rid of it as it most probably impacts performance.

When thinking of a fix my first thought was to do an instanceof check of the result of g.getCoordinate() in writeGeometry. But that would be pretty ugly. Is there a better way to get the subtype of the Coordinate (whether it is CoordinateXYM)?

When looking at the WKTWriter there is the method setOutputOrdinates() . I was using this method to correctly write XYM coordinates as text, so I think this pattern may be applied to the WTBWriter as well. Do you have other ideas?

kaiwinter added a commit to kaiwinter/jts that referenced this issue May 26, 2021
@kaiwinter
Unit test for locationtech#733
518ccd0 
M coordinate is read as Z coordinate after writing/reading.
kaiwinter added a commit to kaiwinter/jts that referenced this issue May 28, 2021
@kaiwinter
Fixed lost M coordinates (locationtech#733)
d747acf 
Referring to WKTReader/WKTWriter I added the EnumSet<Ordinate>
ordinateFlags. The WKBWriter uses these ordinateFlags to set the correct
flags on the byte stream.
kaiwinter added a commit to kaiwinter/jts that referenced this issue May 28, 2021
@kaiwinter
Fixed lost M coordinates (locationtech#733)
7b02318 
Referring to WKTReader/WKTWriter I added the EnumSet<Ordinate>
ordinateFlags. The WKBWriter uses these ordinateFlags to set the correct
flags on the byte stream.

Signed-off-by: Kai Winter <[email protected]>
kaiwinter added a commit to kaiwinter/jts that referenced this issue Aug 23, 2024
@kaiwinter
Unit test for locationtech#733
783a059 
M coordinate is read as Z coordinate after writing/reading.
kaiwinter added a commit to kaiwinter/jts that referenced this issue Aug 23, 2024
@kaiwinter
Fixed lost M coordinates (locationtech#733)
e5d4ae0 
Referring to WKTReader/WKTWriter I added the EnumSet<Ordinate>
ordinateFlags. The WKBWriter uses these ordinateFlags to set the correct
flags on the byte stream.

Signed-off-by: Kai Winter <[email protected]>
jodygarnett pushed a commit that referenced this issue Aug 26, 2024
@kaiwinter
Keep M coordinates when writing to WKB and reading from WKB (#734)
96805bb 
* Unit test for #733

M coordinate is read as Z coordinate after writing/reading.

* Fixed lost M coordinates (#733)

Referring to WKTReader/WKTWriter I added the EnumSet<Ordinate>
ordinateFlags. The WKBWriter uses these ordinateFlags to set the correct
flags on the byte stream.

Signed-off-by: Kai Winter <[email protected]>

* Fixed Javadoc and exception message

* Fixed handling of XYZM coordinates

Signed-off-by: Kai Winter <[email protected]>
# Conflicts:
#	modules/core/src/main/java/org/locationtech/jts/io/WKBWriter.java

---------

Signed-off-by: Kai Winter <[email protected]>
@Kontinuation Kontinuation linked a pull request Oct 17, 2024 that will close this issue
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Fix writing XYM geometries as WKB Kontinuation/jts
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@kaiwinter @jnh5y