What's the expected user input for CoordinateSystem.from_user_input

[originlake]

Hi, I'm trying to create a custom 3D CRS with the elevation defined as the ellipsoid height. As the is no existing Cartesian 3D CS, I try to build one with wkt string, but I don't know what's the right format it should be, even the wkt string generated directly from a existing CRS does not work. Did I miss something?

from pyproj import CRS
from pyproj.crs.coordinate_system import CoordinateSystem
cs_wkt = CRS("EPSG:4326").coordinate_system.to_wkt()
print(cs_wkt)
CoordinateSystem.from_user_input(cs_wkt)

[jjimenezshaw]

You can easily create it via the command line.
For instance this

projinfo EPSG:2056 --3d
...
PROJCRS["CH1903+ / LV95",
    BASEGEOGCRS["CH1903+",
        DATUM["CH1903+",
            ELLIPSOID["Bessel 1841",6377397.155,299.1528128,
                LENGTHUNIT["metre",1]],
            ID["EPSG",6150]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8901]]],
    CONVERSION["Swiss Oblique Mercator 1995",
        METHOD["Hotine Oblique Mercator (variant B)",
            ID["EPSG",9815]],
        PARAMETER["Latitude of projection centre",46.9524055555556,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8811]],
        PARAMETER["Longitude of projection centre",7.43958333333333,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8812]],
        PARAMETER["Azimuth at projection centre",90,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8813]],
        PARAMETER["Angle from Rectified to Skew Grid",90,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8814]],
        PARAMETER["Scale factor at projection centre",1,
            SCALEUNIT["unity",1],
            ID["EPSG",8815]],
        PARAMETER["Easting at projection centre",2600000,
            LENGTHUNIT["metre",1],
            ID["EPSG",8816]],
        PARAMETER["Northing at projection centre",1200000,
            LENGTHUNIT["metre",1],
            ID["EPSG",8817]],
        ID["EPSG",19950]],
    CS[Cartesian,3],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
        AXIS["ellipsoidal height (h)",up,
            ORDER[3],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
    USAGE[
        SCOPE["unknown"],
        AREA["Liechtenstein; Switzerland."],
        BBOX[45.82,5.96,47.81,10.49]],
    REMARK["Promoted to 3D from EPSG:2056"]]

See that the Z is generated in meters, regardless the horizontal unit. You can easily change it.

[originlake]

Thanks, I was trying to construct a custom CRS with the custom classes provided in pyproj, but the coordinate system became the rock-block for me due to there is no custom class provided, then I found the from_user_input method couldn't handle wkt. I will use json format instead following @snowman2 recommendation.

[snowman2]

The method CRS.to_3d will likely be helpful for you to get started.

from pyproj import CRS
cs_wkt = CRS("EPSG:4326").to_3d().coordinate_system

[snowman2]

The coordinate system API may be a helpful resource as well:

from pyproj.crs.coordinate_system import Ellipsoidal3DCS
from pyproj.crs.enums import Ellipsoidal3DCSAxis

vcs = Ellipsoidal3DCS(axis=Ellipsoidal3DCSAxis.LATITUDE_LONGITUDE_HEIGHT)

[snowman2]

Should probably document this better, but WKT & coordinate systems don't mix well together: OSGeo/PROJ#1819

I recommend using to_json/from_json instead.

[originlake]

I'm working on a custom CRS where the coordinate system should be cartesian 3d, and I also want to control the unit of it. That's why I'm checking how to instantiate one via the WKT string. I'll use the json format to do it instead. Thanks for pointing out the reason.

Do you think it'll be better if pyproj can expose the coordinate system constructor and axis constructor similar to the Datum related custom classes(CustomDatum, CustomEllipsoid etc)? Which would be more intuitive to use IMHO.

[snowman2]

It would probably be worthwhile to add a relaxed constructor. Feel free to open an issue.