[gdal-dev] [Question] PROJ4String to WKT2 Transformations

[Rahkonen Jukka (MML)]

Hi,

The more or less same question seems to be asked some time ago in gis.stackexchange https://gis.stackexchange.com/questions/420378/can-we-construct-wkt2-from-proj4string-correctly.

-Jukka Rahkonen-


Lähettäjä: gdal-dev <gdal-dev-bounces at lists.osgeo.org> Puolesta Felipe Matas via gdal-dev
Lähetetty: maanantai 10. tammikuuta 2022 22.07
Vastaanottaja: gdal-dev at lists.osgeo.org
Aihe: [gdal-dev] [Question] PROJ4String to WKT2 Transformations

Hi hi, I was looking for someplace to ask about this, and I was in doubt is was here or in PROJ, but lets do a try.

Actually, probably I'm not the only one, I have some questions about how WKT2 and PROJ4Strings are transformed.

From what I read, a PROJ4String don't have enough info to construct a precise WKT2, so, actually how PROJ4String is deprecated my main question is how to construct the right WKT2, there is a lot o data stored in the old format, there is usually no more information, and even the software/hardware that get the data in some way save all of it with all the errors.

Actually, we can transform a old CRS to a WKT2:


> st_crs("+type=crs +proj=utm +zone=19 +south +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0"

+ )

Coordinate Reference System:

  User input: +type=crs +proj=utm +zone=19 +south +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0

  wkt:

BOUNDCRS[

    SOURCECRS[

        PROJCRS["unknown",

            BASEGEOGCRS["unknown",

                DATUM["World Geodetic System 1984",

                    ELLIPSOID["WGS 84",6378137,298.257223563,

                        LENGTHUNIT["metre",1]],

                    ID["EPSG",6326]],

                PRIMEM["Greenwich",0,

                    ANGLEUNIT["degree",0.0174532925199433],

                    ID["EPSG",8901]]],

            CONVERSION["UTM zone 19S",

                METHOD["Transverse Mercator",

                    ID["EPSG",9807]],

                PARAMETER["Latitude of natural origin",0,

                    ANGLEUNIT["degree",0.0174532925199433],

                    ID["EPSG",8801]],

                PARAMETER["Longitude of natural origin",-69,

                    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["EPSG",17019]],

            CS[Cartesian,2],

                AXIS["(E)",east,

                    ORDER[1],

                    LENGTHUNIT["metre",1,

                        ID["EPSG",9001]]],

                AXIS["(N)",north,

                    ORDER[2],

                    LENGTHUNIT["metre",1,

                        ID["EPSG",9001]]]]],

    TARGETCRS[

        GEOGCRS["WGS 84",

            DATUM["World Geodetic System 1984",

                ELLIPSOID["WGS 84",6378137,298.257223563,

                    LENGTHUNIT["metre",1]]],

            PRIMEM["Greenwich",0,

                ANGLEUNIT["degree",0.0174532925199433]],

            CS[ellipsoidal,2],

                AXIS["latitude",north,

                    ORDER[1],

                    ANGLEUNIT["degree",0.0174532925199433]],

                AXIS["longitude",east,

                    ORDER[2],

                    ANGLEUNIT["degree",0.0174532925199433]],

            ID["EPSG",4326]]],

    ABRIDGEDTRANSFORMATION["Transformation from unknown to WGS84",

        METHOD["Geocentric translations (geog2D domain)",

            ID["EPSG",9603]],

        PARAMETER["X-axis translation",0,

            ID["EPSG",8605]],

        PARAMETER["Y-axis translation",0,

            ID["EPSG",8606]],

        PARAMETER["Z-axis translation",0,

            ID["EPSG",8607]]]]

So, in some way, GDAL is able to cover this "breach" of information betwen PROJ4String and WKT2, but is not like the breach does not exist, it was just handled in some way, so, the lack of info, also means, there can be othe aproximations to that CRS.

Maybe I'm just confused, and mixing things the things I read, I'm just trying to figure it out, what and how would be the right transformation from proj4string to wkt2.

Thx.

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