Problems defining custom CRS in QGIS - Orthographic projection

Question

Working with QGIS 3.14 on Win 10, I try to define a custom CRS - I want to create an Orthographic projection centered on the Mediterranean - 35 N 20 E.

What I did: I copied the WKT-definition of North Pole Orthographic ESRI:102035 from the project properties CRS dialogue and than used this definition as starting point, pasted it in the custom CRS dialogue and changed the values from

PARAMETER["Latitude of natural origin",90,

and

PARAMETER["Longitude of natural origin",0,

to

PARAMETER["Latitude of natural origin",35,

and

PARAMETER["Longitude of natural origin",20,

So the changed WKT-definition looks like this:

PROJCRS["Mediterranean_Orthographic",
    BASEGEOGCRS["WGS 84",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["Degree",0.0174532925199433]]],
    CONVERSION["North_Pole_Orthographic",
        METHOD["Orthographic",
            ID["EPSG",9840]],
        PARAMETER["Latitude of natural origin",35,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",20,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["False easting",0,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",0,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1]],
    USAGE[
        SCOPE["unknown"],
        AREA["World - north of 0°N"],
        BBOX[0,-180,90,180]],
    ID["ESRI",102035]]
Proj4
+proj=ortho +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
Ausdehnung
-180.00, 0.00, 180.00, 90.00

Clicking the validate button, it tells me the defintion is valid. When I try to click OK to save the changes, an error message pops up:

PROJ-string ist equivalent to ESRI:102035
Please try to change the CRS-definition in WKT-format

Found this here, but it did not really help: Create new custom projections in QGIS 3.12?

How can I keep the original North_Pole_Orthographic (ESRI:102035) definition and add an additional one, just centered on another point?

Answer 1

You should only copy the WKT part. The Proj4 and Extent section should not go to the WKT parser as they are not parts of the WKT definition. Also, ID["ESRI",102035]] has to be removed. Otherwise the ID points to an existing CRS and causes the "is equivalent" error.

This is what you need:

PROJCRS["North_Pole_Orthographic",
BASEGEOGCRS["WGS 84",
    DATUM["World Geodetic System 1984",
        ELLIPSOID["WGS 84",6378137,298.257223563,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["Degree",0.0174532925199433]]],
CONVERSION["North_Pole_Orthographic",
    METHOD["Orthographic",
        ID["EPSG",9840]],
    PARAMETER["Latitude of natural origin",35,
        ANGLEUNIT["Degree",0.0174532925199433],
        ID["EPSG",8801]],
    PARAMETER["Longitude of natural origin",20,
        ANGLEUNIT["Degree",0.0174532925199433],
        ID["EPSG",8802]],
    PARAMETER["False easting",0,
        LENGTHUNIT["metre",1],
        ID["EPSG",8806]],
    PARAMETER["False northing",0,
        LENGTHUNIT["metre",1],
        ID["EPSG",8807]]],
CS[Cartesian,2],
    AXIS["(E)",east,
        ORDER[1],
        LENGTHUNIT["metre",1]],
    AXIS["(N)",north,
        ORDER[2],
        LENGTHUNIT["metre",1]],
USAGE[
    SCOPE["unknown"],
    AREA["World - north of 0?N"],
    BBOX[0,-180,90,180]]]