Difference between revisions of "RFC-001"

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(Added multi-s, polygon exterior and holes, and examples of all geometry types)
(Fixed Multi examples, strengthened EPSG/PROJ.4 reference, and shuffled some text)
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Inspired in part by http://trac.gispython.org/projects/PCL/wiki/PythonFeatureProtocol (or maybe even a complete copy )
 
 
 
== Definitions ==
 
== Definitions ==
* The terms object, name, value, array, and number are defined at http://json.org/
+
 
 +
* JavaScript Object Notation (JSON), and the terms object, name, value, array, and number, are defined at http://json.org/
 
* The terms may, should, and must are defined at http://www.ietf.org/rfc/rfc2119.txt
 
* The terms may, should, and must are defined at http://www.ietf.org/rfc/rfc2119.txt
  
Line 20: Line 19:
 
#*** 'type' - LinearRing
 
#*** 'type' - LinearRing
 
#*** 'coordinates' - An array of coordinates as defined above, restricted as follows:
 
#*** 'coordinates' - An array of coordinates as defined above, restricted as follows:
#**** A LinearRing must have at least four coordinates, with the first and last coordinates coincident, i.e. the geometry is closed.
+
#**** A LinearRing must have at least four coordinates, with the first and last coordinates coincident, i.e. the geometry must be closed.
 
#** A Polygon may have a 'holes' name/value pair.  The value of holes must itself be an array of geometries of type LinearRing, as defined for exterior.  If present, the array must contain at least one LinearRing.
 
#** A Polygon may have a 'holes' name/value pair.  The value of holes must itself be an array of geometries of type LinearRing, as defined for exterior.  If present, the array must contain at least one LinearRing.
 
#* For 'type' [MultiLineString | MultiPolygon | GeometryCollection]:
 
#* For 'type' [MultiLineString | MultiPolygon | GeometryCollection]:
Line 28: Line 27:
 
#*** A GeometryCollection must contain only Point, LineString or Polygon geometry objects.
 
#*** A GeometryCollection must contain only Point, LineString or Polygon geometry objects.
 
#*** In all cases, the members must not contain a 'crs' value.
 
#*** In all cases, the members must not contain a 'crs' value.
#* 'crs' - an optional string specifying a coordinate reference system of the coordinates. If not present, WGS84 is implied and coordinates represent decimal degrees ordered as "longitude, latitude [,elevation]" and z is expressed as meters above mean sea level per WGS84. If present, the value of crs is to be interpreted as in PROJ4's EPSG tables and the values of the coordinates are to be interpreted accordingly.
+
#* 'crs' - an optional string specifying a coordinate reference system of the coordinates. If not present, WGS84 is implied and coordinates represent decimal degrees ordered as "longitude, latitude [,elevation]" with z expressed as metres above mean sea level per WGS84. If present, the value of crs must be of the form 'EPSG:nnnn', where 'nnnn' represents the [[#EPSG|EPSG]] crs code.
 
# A feature should have a name/value pair whose name is 'id' and whose value can be uniquely interpreted by the source of the GeoJSON string,  generally identifying this GeoJSON object's resource.
 
# A feature should have a name/value pair whose name is 'id' and whose value can be uniquely interpreted by the source of the GeoJSON string,  generally identifying this GeoJSON object's resource.
 
# A feature should have a name/value pair whose name is 'properties'  and whose value is an object that has meaning within a specific community of interest.
 
# A feature should have a name/value pair whose name is 'properties'  and whose value is an object that has meaning within a specific community of interest.
# A feature having multiple geometries should have an array of geometries contained within a properties object (see 5) which is called 'geometries'  and whose values are as described in 3.
+
# A feature having multiple geometries should have an array of geometries contained within a properties object (see 5) which is called 'geometries'  and whose values are as described in rule 3.
 +
 
 +
== References ==
 +
=== GISPython: Feature Protocol ===
 +
GeoJSON is inspired in part by http://trac.gispython.org/projects/PCL/wiki/PythonFeatureProtocol (or maybe even a complete copy).
 +
 
 +
=== EPSG ===
 +
The [http://www.ogp.org.uk International Associated of Oil & Gas Producers (OGP)] [http://www.epsg.org publishes] a widely used and widely referenced database of well-known coordinate reference systems.  The database was previously published by the European Petroluem Survey Group (EPSG), before EPSG was absorbed into OGP.  The EPSG/OGP database references each crs by code number, e.g. EPSG code 4326 is a geographic (latitude/longitude) crs, using the WGS84 datum.
 +
==== GeoJSON Exceptions ====
 +
* GeoJSON References to a EPSG crs are consistent with programming convention, for example in the [http://www.remotesensing.org/proj PROJ.4] library, not geodetic convention:
 +
*# When referencing a geographic crs "longitude, latitude [, elevetion]" coordinate order is implied.
 +
*# When referencing a projected crs "easting, northing [, elevation]" coordinate order is implied.
  
 
== Examples ==
 
== Examples ==
 
=== Features ===
 
=== Features ===
adapted from Python example at [http://trac.gispython.org/projects/PCL/wiki/PythonFeatureProtocol GISPython: Feature Protocol]
+
Adapted from Python example at [http://trac.gispython.org/projects/PCL/wiki/PythonFeatureProtocol GISPython: Feature Protocol]
  {  
+
 
 +
  {
 
   "id": "1",
 
   "id": "1",
 
   "properties": {
 
   "properties": {
 
     "title": "Feature 1",
 
     "title": "Feature 1",
 
     "summary": "The first feature",
 
     "summary": "The first feature",
     "link": "http:example.org/features/1"
+
     "link": "<nowiki>http://example.org/features/1</nowiki>"
 
   },
 
   },
 
   "geometry": {
 
   "geometry": {
 
     "type": "Point",
 
     "type": "Point",
     "coordinates": <nowiki>[[-105.8, 40.05]]</nowiki>
+
     "coordinates": <nowiki>[[0.0,0.0]]</nowiki>
 
   }
 
   }
 
  }
 
  }
 +
 +
As in JSON, whitespace is irrelevant::
 +
 +
{"id":"2","properties":{"title":"Feature 2","geometry":{"type":"Point","coordinates":<nowiki>[[1.0,1.0]]</nowiki>}}
  
 
=== Geometries ===
 
=== Geometries ===
  
Each example is presented in isolation, without the containing feature object.
+
Each example is presented in isolation, without the containing feature object. The 'crs' name/value pair is included for reference only, 'EPSG:4326' being equivalent to having no 'crs' name/value pair at all.
  
 
==== Point ====
 
==== Point ====
 
   "geometry": {
 
   "geometry": {
 
     "type": "Point",
 
     "type": "Point",
 +
    "crs": "EPSG:4326",
 
     "coordinates": <nowiki>[[0.0,0.0]]</nowiki>
 
     "coordinates": <nowiki>[[0.0,0.0]]</nowiki>
 
   }
 
   }
Line 62: Line 78:
 
   "geometry": {
 
   "geometry": {
 
     "type": "LineString",
 
     "type": "LineString",
 +
    "crs": "EPSG:4326",
 
     "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0]]</nowiki>
 
     "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0]]</nowiki>
 
   }
 
   }
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   "geometry": {
 
   "geometry": {
 
     "type": "Polygon",
 
     "type": "Polygon",
     "exterior":{
+
    "crs": "EPSG:4326",
       "type":"LinearRing",
+
     "exterior": {
 +
       "type": "LinearRing",
 
       "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]</nowiki>
 
       "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]</nowiki>
 
     }
 
     }
 
     "holes":[
 
     "holes":[
 
       {
 
       {
         "type":"LinearRing",
+
         "type": "LinearRing",
 
         "coordinates": <nowiki>[[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]</nowiki>
 
         "coordinates": <nowiki>[[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]</nowiki>
 
       }
 
       }
Line 83: Line 101:
 
   "geometry": {
 
   "geometry": {
 
     "type": "Box",
 
     "type": "Box",
 +
    "crs": "EPSG:4326",
 
     "coordinates": <nowiki>[[0.0,0.0],[1.0,1.0]]</nowiki>
 
     "coordinates": <nowiki>[[0.0,0.0],[1.0,1.0]]</nowiki>
 
   }
 
   }
Line 89: Line 108:
 
   "geometry": {
 
   "geometry": {
 
     "type": "MultiPoint",
 
     "type": "MultiPoint",
 +
    "crs": "EPSG:4326",
 
     "coordinates": <nowiki>[[0.0,0.0],[1.0,1.0]]</nowiki>
 
     "coordinates": <nowiki>[[0.0,0.0],[1.0,1.0]]</nowiki>
 
   }
 
   }
  
 
==== MultiLineString ====
 
==== MultiLineString ====
   "members": [
+
   "geometry": {
    "geometry": {
+
    "type": "MultiLineString",
      "type": "LineString",
+
    "crs": "EPSG:4326",
      "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0]]</nowiki>
+
    "members": [
    },
+
      "geometry": {
    "geometry": {
+
        "type": "LineString",
      "type": "LineString",
+
        "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0]]</nowiki>
      "coordinates": <nowiki>[[2.0,2.0],[3.0,2.0],[3.0,3.0]]</nowiki>
+
      },
    }
+
      "geometry": {
  ]
+
        "type": "LineString",
 +
        "coordinates": <nowiki>[[2.0,2.0],[3.0,2.0],[3.0,3.0]]</nowiki>
 +
      }
 +
    ]
 +
  }
  
 
==== MultiPolygon ====
 
==== MultiPolygon ====
   "members": [
+
   "geometry": {
    "geometry": {
+
    "type": "MultiPolygon",
      "type": "Polygon",
+
    "crs": "EPSG:4326",
      "exterior":{
+
    "members": [
        "type":"LinearRing",
+
      "geometry": {
        "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]</nowiki>
+
        "type": "Polygon",
      }
+
        "exterior": {
      "holes":[
+
          "type": "LinearRing",
        {
+
          "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]</nowiki>
          "type":"LinearRing",
+
        }
          "coordinates": <nowiki>[[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]</nowiki>
+
        "holes":[
 +
          {
 +
            "type": "LinearRing",
 +
            "coordinates": <nowiki>[[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]</nowiki>
 +
          }
 +
        ]
 +
      },
 +
      "geometry": {
 +
        "type": "Polygon",
 +
        "exterior": {
 +
          "type": "LinearRing",
 +
          "coordinates": <nowiki>[[10.0,10.0],[11.0,0.0],[11.0,11.0],[10.0,11.0],[10.0,10.0]]</nowiki>
 
         }
 
         }
      ]
 
    },
 
    "geometry": {
 
      "type": "Polygon",
 
      "exterior":{
 
        "type":"LinearRing",
 
        "coordinates": <nowiki>[[10.0,10.0],[11.0,0.0],[11.0,11.0],[10.0,11.0],[10.0,10.0]]</nowiki>
 
 
       }
 
       }
     }
+
     ]
   ]
+
   }
  
 
==== GeometryCollection ====
 
==== GeometryCollection ====
   "members": [
+
   "geometry": {
    "geometry": {
+
    "type": "GeometryCollection",
      "type": "Point",
+
    "crs": "EPSG:4326",
      "coordinates": <nowiki>[[0.0,0.0]]</nowiki>
+
    "members": [
    },
+
      "geometry": {
    "geometry": {
+
        "type": "Point",
      "type": "LineString",
+
        "coordinates": <nowiki>[[0.0,0.0]]</nowiki>
      "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0]]</nowiki>
+
      },
    },
+
      "geometry": {
    "geometry": {
+
        "type": "LineString",
      "type": "Polygon",
+
        "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0]]</nowiki>
      "exterior":{
+
      },
        "type":"LinearRing",
+
      "geometry": {
        "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]</nowiki>
+
        "type": "Polygon",
      }
+
        "exterior": {
      "holes":[
+
          "type": "LinearRing",
        {
+
          "coordinates": <nowiki>[[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]</nowiki>
          "type":"LinearRing",
+
          "coordinates": <nowiki>[[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]</nowiki>
+
 
         }
 
         }
      ]
+
        "holes":[
    },
+
          {
  ]
+
            "type": "LinearRing",
 +
            "coordinates": <nowiki>[[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]</nowiki>
 +
          }
 +
        ]
 +
      }
 +
    ]
 +
  }
  
 
==Authors==
 
==Authors==

Revision as of 04:18, 24 April 2007

Definitions

Specification

  1. A feature is an object.
  2. A feature may have a name/value pair whose name is 'geometry' and whose value conforms to rule 3. (A feature may have any other name/value pairs, without restriction.)
  3. The value of a geometry must itself be an object with the following name/value pairs:
    • 'type' - [Point | LineString | Polygon | Box | MultiPoint | MultiLineString | MultiPolygon | GeometryCollection]
    • For 'type' [Point | LineString | Box | MultiPoint]:
      • 'coordinates' - A coordinate consists of an array of two or three number values representing x, y, and optionally z. In the case of a Point, the value of coordinates is an array consisting of a single coordinate (i.e. an array of two or three number values). In all other cases, an array of coordinates as in Point, restricted as follows:
        • A LineString must have at least two coordinates.
        • A Box must have exactly two coordinates.
        • A MultiPoint must have at least two coordinates.
    • For 'type' [Polygon]:
      • 'exterior' - The value of an exterior must itself be a geometry object with the following name/value pairs:
        • 'type' - LinearRing
        • 'coordinates' - An array of coordinates as defined above, restricted as follows:
          • A LinearRing must have at least four coordinates, with the first and last coordinates coincident, i.e. the geometry must be closed.
      • A Polygon may have a 'holes' name/value pair. The value of holes must itself be an array of geometries of type LinearRing, as defined for exterior. If present, the array must contain at least one LinearRing.
    • For 'type' [MultiLineString | MultiPolygon | GeometryCollection]:
      • 'members' - The value of members must be an array of geometry objects, restricted as follows:
        • A MultiLineString must contain only LineString geometry objects.
        • A MultiPolygon must contain only Polygon geometry objects.
        • A GeometryCollection must contain only Point, LineString or Polygon geometry objects.
        • In all cases, the members must not contain a 'crs' value.
    • 'crs' - an optional string specifying a coordinate reference system of the coordinates. If not present, WGS84 is implied and coordinates represent decimal degrees ordered as "longitude, latitude [,elevation]" with z expressed as metres above mean sea level per WGS84. If present, the value of crs must be of the form 'EPSG:nnnn', where 'nnnn' represents the EPSG crs code.
  4. A feature should have a name/value pair whose name is 'id' and whose value can be uniquely interpreted by the source of the GeoJSON string, generally identifying this GeoJSON object's resource.
  5. A feature should have a name/value pair whose name is 'properties' and whose value is an object that has meaning within a specific community of interest.
  6. A feature having multiple geometries should have an array of geometries contained within a properties object (see 5) which is called 'geometries' and whose values are as described in rule 3.

References

GISPython: Feature Protocol

GeoJSON is inspired in part by http://trac.gispython.org/projects/PCL/wiki/PythonFeatureProtocol (or maybe even a complete copy).

EPSG

The International Associated of Oil & Gas Producers (OGP) publishes a widely used and widely referenced database of well-known coordinate reference systems. The database was previously published by the European Petroluem Survey Group (EPSG), before EPSG was absorbed into OGP. The EPSG/OGP database references each crs by code number, e.g. EPSG code 4326 is a geographic (latitude/longitude) crs, using the WGS84 datum.

GeoJSON Exceptions

  • GeoJSON References to a EPSG crs are consistent with programming convention, for example in the PROJ.4 library, not geodetic convention:
    1. When referencing a geographic crs "longitude, latitude [, elevetion]" coordinate order is implied.
    2. When referencing a projected crs "easting, northing [, elevation]" coordinate order is implied.

Examples

Features

Adapted from Python example at GISPython: Feature Protocol

{
  "id": "1",
  "properties": {
    "title": "Feature 1",
    "summary": "The first feature",
    "link": "http://example.org/features/1"
  },
  "geometry": {
    "type": "Point",
    "coordinates": [[0.0,0.0]]
  }
}

As in JSON, whitespace is irrelevant::

{"id":"2","properties":{"title":"Feature 2","geometry":{"type":"Point","coordinates":[[1.0,1.0]]}}

Geometries

Each example is presented in isolation, without the containing feature object. The 'crs' name/value pair is included for reference only, 'EPSG:4326' being equivalent to having no 'crs' name/value pair at all.

Point

  "geometry": {
    "type": "Point",
    "crs": "EPSG:4326",
    "coordinates": [[0.0,0.0]]
  }

LineString

  "geometry": {
    "type": "LineString",
    "crs": "EPSG:4326",
    "coordinates": [[0.0,0.0],[1.0,0.0],[1.0,1.0]]
  }

Polygon

  "geometry": {
    "type": "Polygon",
    "crs": "EPSG:4326",
    "exterior": {
      "type": "LinearRing",
      "coordinates": [[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]
    }
    "holes":[
      {
        "type": "LinearRing",
        "coordinates": [[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]
      }
    ]
  }

Box

  "geometry": {
    "type": "Box",
    "crs": "EPSG:4326",
    "coordinates": [[0.0,0.0],[1.0,1.0]]
  }

MultiPoint

  "geometry": {
    "type": "MultiPoint",
    "crs": "EPSG:4326",
    "coordinates": [[0.0,0.0],[1.0,1.0]]
  }

MultiLineString

  "geometry": {
    "type": "MultiLineString",
    "crs": "EPSG:4326",
    "members": [
      "geometry": {
        "type": "LineString",
        "coordinates": [[0.0,0.0],[1.0,0.0],[1.0,1.0]]
      },
      "geometry": {
        "type": "LineString",
        "coordinates": [[2.0,2.0],[3.0,2.0],[3.0,3.0]]
      }
    ]
  }

MultiPolygon

  "geometry": {
    "type": "MultiPolygon",
    "crs": "EPSG:4326",
    "members": [
      "geometry": {
        "type": "Polygon",
        "exterior": {
          "type": "LinearRing",
          "coordinates": [[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]
        }
        "holes":[
          {
            "type": "LinearRing",
            "coordinates": [[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]
          }
        ]
      },
      "geometry": {
        "type": "Polygon",
        "exterior": {
          "type": "LinearRing",
          "coordinates": [[10.0,10.0],[11.0,0.0],[11.0,11.0],[10.0,11.0],[10.0,10.0]]
        }
      }
    ]
  }

GeometryCollection

  "geometry": {
    "type": "GeometryCollection",
    "crs": "EPSG:4326",
    "members": [
      "geometry": {
        "type": "Point",
        "coordinates": [[0.0,0.0]]
      },
      "geometry": {
        "type": "LineString",
        "coordinates": [[0.0,0.0],[1.0,0.0],[1.0,1.0]]
      },
      "geometry": {
        "type": "Polygon",
        "exterior": {
          "type": "LinearRing",
          "coordinates": [[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0],[0.0,0.0]]
        }
        "holes":[
          {
            "type": "LinearRing",
            "coordinates": [[0.25,0.25],[0.75,0.25],[0.75,0.75],[0.25,0.75],[0.25,0.25]]
          }
        ]
      }
    ]
 }

Authors

  • Allan Doyle
  • Sean Gillies
  • Martin Daly