Scope, remarks missing from WKT?

[snowman2]

Related to #2237 as this recently popped up after the change.

This is more of a question as I am just verifying that this behavior is expected.

Example of problem

When creating a transformer using proj_create_operations:

>>> from pyproj.transformer import TransformerGroup
>>> transformer = TransformerGroup(28356, 7856).transformers[0]

I can get the operations using proj_concatoperation_get_step.

However, for some reason the WKT does not have the scope & remarks for this operation even through it is present on the operation step:

>>> print(transformer.operations[0].to_wkt(pretty=True))
CONVERSION["Inverse of Map Grid of Australia zone 56",
    METHOD["Inverse of Transverse Mercator",
        ID["INVERSE(EPSG)",9807]],
    PARAMETER["Latitude of natural origin",0,
        ANGLEUNIT["degree",0.0174532925199433],
        ID["EPSG",8801]],
    PARAMETER["Longitude of natural origin",153,
        ANGLEUNIT["degree",0.0174532925199433],
        ID["EPSG",8802]],
    PARAMETER["Scale factor at natural origin",0.9996,
        SCALEUNIT["unity",1],
        ID["EPSG",8805]],
    PARAMETER["False easting",500000,
        LENGTHUNIT["metre",1],
        ID["EPSG",8806]],
    PARAMETER["False northing",10000000,
        LENGTHUNIT["metre",1],
        ID["EPSG",8807]],
    ID["INVERSE(EPSG)",17356]]
>>> transformer.operations[0].scope
'Large and medium scale topographic mapping and engineering survey.'
>>> transformer.operations[0].remarks
'Grid convergence uses opposite sign convention to UTM.'

But, on the next operation step, it is present in the WKT:

>>> print(transformer.operations[1].to_wkt(pretty=True))
COORDINATEOPERATION["GDA94 to GDA2020 (1)",
    VERSION["ICSM-Aus"],
    SOURCECRS[
        GEOGCRS["GDA94",
            DATUM["Geocentric Datum of Australia 1994",
                ELLIPSOID["GRS 1980",6378137,298.257222101,
                    LENGTHUNIT["metre",1]]],
            PRIMEM["Greenwich",0,
                ANGLEUNIT["degree",0.0174532925199433]],
            CS[ellipsoidal,2],
                AXIS["geodetic latitude (Lat)",north,
                    ORDER[1],
                    ANGLEUNIT["degree",0.0174532925199433]],
                AXIS["geodetic longitude (Lon)",east,
                    ORDER[2],
                    ANGLEUNIT["degree",0.0174532925199433]],
            ID["EPSG",4283]]],
    TARGETCRS[
        GEOGCRS["GDA2020",
            DATUM["Geocentric Datum of Australia 2020",
                ELLIPSOID["GRS 1980",6378137,298.257222101,
                    LENGTHUNIT["metre",1]]],
            PRIMEM["Greenwich",0,
                ANGLEUNIT["degree",0.0174532925199433]],
            CS[ellipsoidal,2],
                AXIS["geodetic latitude (Lat)",north,
                    ORDER[1],
                    ANGLEUNIT["degree",0.0174532925199433]],
                AXIS["geodetic longitude (Lon)",east,
                    ORDER[2],
                    ANGLEUNIT["degree",0.0174532925199433]],
            ID["EPSG",7844]]],
    METHOD["Coordinate Frame rotation (geog2D domain)",
        ID["EPSG",9607]],
    PARAMETER["X-axis translation",61.55,
        LENGTHUNIT["millimetre",0.001],
        ID["EPSG",8605]],
    PARAMETER["Y-axis translation",-10.87,
        LENGTHUNIT["millimetre",0.001],
        ID["EPSG",8606]],
    PARAMETER["Z-axis translation",-40.19,
        LENGTHUNIT["millimetre",0.001],
        ID["EPSG",8607]],
    PARAMETER["X-axis rotation",-39.4924,
        ANGLEUNIT["milliarc-second",4.84813681109536E-09],
        ID["EPSG",8608]],
    PARAMETER["Y-axis rotation",-32.7221,
        ANGLEUNIT["milliarc-second",4.84813681109536E-09],
        ID["EPSG",8609]],
    PARAMETER["Z-axis rotation",-32.8979,
        ANGLEUNIT["milliarc-second",4.84813681109536E-09],
        ID["EPSG",8610]],
    PARAMETER["Scale difference",-9.994,
        SCALEUNIT["parts per billion",1E-09],
        ID["EPSG",8611]],
    OPERATIONACCURACY[0.01],
    USAGE[
        SCOPE["Conformal transformation of GDA94 coordinates that have been derived through GNSS CORS."],
        AREA["Australia - GDA"],
        BBOX[-60.56,93.41,-8.47,173.35]],
    ID["EPSG",8048],
    REMARK["Scale difference in ppb where 1/billion = 1E-9. See CT codes 8444-46 for NTv2 method giving equivalent results for Christmas Island, Cocos Islands and Australia respectively. See CT code 8447 for alternative including distortion model for Australia only."]]

Is this a limitation of the WKT format?

Environment Information

• PROJ version 7.1.0
• Operation System Information - Linux-4.15.0-101-generic-x86_64-with-glibc2.10

Installation method

• From source

[rouault]

Is this a limitation of the WKT format?

yes. The BNF grammar is at http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#76 . See which only accepts a [ { } ] , contrary to COORDINATEOPERATION ( http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#132 ) whichs accepts . The reason is probably that CONVERSION is not intended to be nominally a standalone object, but embedded in a PROJCRS object (which can have a scope, extent, remark)

[snowman2]

Thanks for verifying that this is expected 👍