projjson.adoc

gistfile1.txt

== PROJJSON

PROJJSON is a JSON encoding of
http://docs.opengeospatial.org/is/18-010r7/18-010r7.html[WKT2:2019 /
ISO-19162:2019], which itself implements the model of
http://docs.opengeospatial.org/as/18-005r4/18-005r4.html[OGC Topic 2:
Referencing by coordinates]. Apart from the difference of encodings, the
semantics is intended to be exactly the same as WKT2:2019.

PROJJSON is available as input and output of PROJ since PROJ 6.2.

The current version is 0.4.

=== Schema

A JSON schema of its grammar is available at
https://proj.org/schemas/v0.4/projjson.schema.json

=== History

* v0.4: additional properties allowed in id object (version,
authority_citation, uri)
* v0.3: additional properties allowed in BoundCRS object (name, scope,
area, bbox, usages, remarks, id, ids)
* v0.2: addition of geoid_model in VerticalCRS object.
* v0.1: initial version for PROJ 6.2

=== Content

The high level objects are:

* Coordinate Reference Systems (CRS):
** Common ones:
*** `GeographicCRS`
*** `GeodeticCRS`
*** `ProjectedCRS`
*** `CompoundCRS`
*** `BoundCRS`
** More esoteric ones:
*** `VerticalCRS`
*** `EngineeringCRS`
*** `TemporalCRS`
*** `ParametricCRS`
*** `DerivedGeographicCRS`
*** `DerivedGeodeticCRS`
*** `DerivedProjectedCRS`
*** `DerivedVerticalCRS`
*** `DerivedEngineeringCRS`
*** `DerivedTemporalCRS`
*** `DerivedParametricCRS`
* Coordinate operations:
** `Transformation`
** `Conversion`
** `ConcatenatedOperation`
* Others:
** `PrimeMeridian`
** `Ellipsoid`
** `Datum`
** `DatumEnsemble`

=== Examples

==== GeographicCRS

The following invocation

....
projinfo EPSG:4326 -o PROJJSON -q
....

will output:

[source,json]
----
{
    "$schema": "https://proj.org/schemas/v0.1/projjson.schema.json",
    "type": "GeographicCRS",
    "name": "WGS 84",
    "datum": {
        "type": "GeodeticReferenceFrame",
        "name": "World Geodetic System 1984",
        "ellipsoid": {
            "name": "WGS 84",
            "semi_major_axis": 6378137,
            "inverse_flattening": 298.257223563
        }
    },
    "coordinate_system": {
        "subtype": "ellipsoidal",
        "axis": [
        {
            "name": "Geodetic latitude",
            "abbreviation": "Lat",
            "direction": "north",
            "unit": "degree"
        },
        {
            "name": "Geodetic longitude",
            "abbreviation": "Lon",
            "direction": "east",
            "unit": "degree"
        }
        ]
    },
    "area": "World",
    "bbox": {
        "south_latitude": -90,
        "west_longitude": -180,
        "north_latitude": 90,
        "east_longitude": 180
    },
    "id": {
        "authority": "EPSG",
        "code": 4326
    }
}
----

==== ProjectedCRS

The following invocation

....
projinfo EPSG:32631 -o PROJJSON -q
....

will output:

[source,json]
----
{
    "$schema": "https://proj.org/schemas/v0.1/projjson.schema.json",
    "type": "ProjectedCRS",
    "name": "WGS 84 / UTM zone 31N",
    "base_crs": {
        "name": "WGS 84",
        "datum": {
            "type": "GeodeticReferenceFrame",
            "name": "World Geodetic System 1984",
            "ellipsoid": {
                "name": "WGS 84",
                "semi_major_axis": 6378137,
                "inverse_flattening": 298.257223563
            }
        },
        "coordinate_system": {
            "subtype": "ellipsoidal",
            "axis": [
            {
                "name": "Geodetic latitude",
                "abbreviation": "Lat",
                "direction": "north",
                "unit": "degree"
            },
            {
                "name": "Geodetic longitude",
                "abbreviation": "Lon",
                "direction": "east",
                "unit": "degree"
            }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 4326
        }
    },
    "conversion": {
        "name": "UTM zone 31N",
        "method": {
            "name": "Transverse Mercator",
            "id": {
                "authority": "EPSG",
                "code": 9807
            }
        },
        "parameters": [
        {
            "name": "Latitude of natural origin",
            "value": 0,
            "unit": "degree",
            "id": {
            "authority": "EPSG",
            "code": 8801
            }
        },
        {
            "name": "Longitude of natural origin",
            "value": 3,
            "unit": "degree",
            "id": {
            "authority": "EPSG",
            "code": 8802
            }
        },
        {
            "name": "Scale factor at natural origin",
            "value": 0.9996,
            "unit": "unity",
            "id": {
            "authority": "EPSG",
            "code": 8805
            }
        },
        {
            "name": "False easting",
            "value": 500000,
            "unit": "metre",
            "id": {
            "authority": "EPSG",
            "code": 8806
            }
        },
        {
            "name": "False northing",
            "value": 0,
            "unit": "metre",
            "id": {
            "authority": "EPSG",
            "code": 8807
            }
        }
        ]
    },
    "coordinate_system": {
        "subtype": "Cartesian",
        "axis": [
        {
            "name": "Easting",
            "abbreviation": "E",
            "direction": "east",
            "unit": "metre"
        },
        {
            "name": "Northing",
            "abbreviation": "N",
            "direction": "north",
            "unit": "metre"
        }
        ]
    },
    "area": "World - N hemisphere - 0°E to 6°E - by country",
    "bbox": {
        "south_latitude": 0,
        "west_longitude": 0,
        "north_latitude": 84,
        "east_longitude": 6
    },
    "id": {
        "authority": "EPSG",
        "code": 32631
    }
}
----