- Qt 6.5
- Qt Location
- QGeoJson Namespace
- Qt 6.5.0 Reference Documentation

# QGeoJson Namespace

The QGeoJson namespace contains functions to import and export geolocated information from and to GeoJson files. More...

Header: | #include <QGeoJson>
qmake: | QT += location

## Functions

QJsonDocument | exportGeoJson(const QVariantList &geoData)
QVariantList | importGeoJson(const QJsonDocument &geoJson)
QString | toString(const QVariantList &geoData)

## Detailed Description

The methods in the QGeoJson namespace can be used to convert between a GeoJSON document (see the Wikipedia page, RFC) and a QVariantList of QVariantMap elements ready to be used as Model in a MapItemView.

Note: This private class is part of Qt labs, thus not stable API, it is part of the experimental components of QtLocation. Until it is promoted to public API, it may be subject to source and binary-breaking changes.

#### Importing GeoJSON

The importGeoJson() method accepts a QJsonDocument from which it extracts a single JSON object. The GeoJSON RFC expects that a valid GeoJSON Document has in its root a single JSON object. This method doesn't perform any validation on the input. The importer returns a QVariantList containing a single QVariantMap. This map has always at least 2 (key, value) pairs. The first one has `type` as key, and the corresponding value is a string identifying the GeoJSON type. This value can be one of the GeoJSON object types: `Point`, `MultiPoint`, `LineString`, `MultiLineString`, `Polygon`, `MultiPolygon`, `GeometryCollection`, `FeatureCollection`. The second pair has `data` as key, and the corresponding value can be either a QGeoShape or a list, depending on the GeoJSON type. The next section provides details about the conversation form GeoJson objects to objects known in Qt Location. The `Feature` type is converted into the type of the geometry contained within, with an additional (key, value) pair, where the key is `properties` and the value is a QVariantMap. Thus, a feature Map is distinguishable from the corresponding geometry, by looking for a `properties` member.

##### Structure of the data node

For the single type geometry objects (`Point`, `LineString`, and `Polygon`), the value corresponding to the `data` key is a QGeoShape:

- When the type is `Point`, the data is a QGeoCircle with the point coordinates stored in the center property.

  For example, the following GeoJSON document contains a `Point` geometry:

       {
         "type" : "Point",
         "data" : [60.0, 11.0]
       }

  it is converted to a QVariantMap with the following structure:

       {
         type : "Point"
         data : QGeoCircle({60.000, 11.000}, -1)
       }

- When the type is `LineString` the data is a QGeoPath.

  For example, the following GeoJSON document contains a `LineString` geometry:

       {
           "type" : "LineString",
           "coordinates" : [[13.5, 43],[10.73, 59.92]]
       }

  it is converted to a QVariantMap with the following structure:

       {
         type : "LineString",
         data : QGeoPath([{43.000, 13.500}, {59.920, 10.730}])
       }

- When the type is `Polygon`, the data is a QGeoPolygon (holes are supported).

  For example, the following GeoJSON document contains a `Polygon` geometry:

       {
           "type" : "Polygon",
           "coordinates" : [
             [[17.13, 51.11],
              [30.54, 50.42],
              [26.70, 58.36],
              [17.13, 51.11]]
           ],
           "bbox" : [60, 60, -60, -60]

       }

  it is converted to a QVariantMap with the following structure:

       {
         type : "Polygon"
         data : QGeoPolygon([{51.110, 17.130}, {50.420,30.540}, {58.360, 26.700}, {51.110, 17.130}])
       }

For the homogeneously typed multipart geometry objects (`MultiPoint`, `MultiLineString`, `MultiPolygon`) the value corresponding to the `data` key is a QVariantList. Each element of the list is a QVariantMap of one of the above listed types. The elements in this list will be all of the same GeoJSON type:

- When the type is `MultiPoint`, the data is a List of Points.

  For example, the following GeoJSON document contains a `MultiPoint` geometry:

       {
           "type" : "MultiPoint",
           "coordinates" : [
             [11,60],
             [5.5,60.3],
             [5.7,58.90]
           ]
       }

  it is converted to a QVariantMap with the following structure:

       {
         type : "MultiPoint"
         data : [
           {
             type : "Point"
             data : QGeoCircle({60.000, 11.000}, -1)
           },
           {
             type : "Point"
             data : QGeoCircle({60.300, 5.500}, -1)
           },
           {
             type : "Point"
             data : QGeoCircle({58.900, 5.700}, -1)
           }
         ]
       }

- When the type is `MultiLineString`, the data is a List of LineStrings.

  For example, the following GeoJSON document contains a `MultiLineString` geometry:

       {
           "type" : "MultiLineString",
           "coordinates" : [
             [[13.5, 43], [10.73, 59.92]],
             [[9.15, 45], [-3.15, 58.90]]
           ]
       }

  it is converted to a QVariantMap with the following structure:

       {
         type : "MultiLineString"
         data : [
           {
             type : "LineString"
             data : QGeoPath([{45.000, 9.150}, {58.900, -3.150}])
           },
           {
             type : "LineString"
             data : QGeoPath([{43.000, 13.500}, {59.920, 10.730}])
           }
         ]
       }

- When the type is `MultiPolygon`, the data is a List of Polygons.

  For example, the following GeoJSON document contains a `MultiPolygon` geometry:

       {
           "type" : "MultiPolygon",
           "coordinates" : [
              [
                [
                  [17.13, 51.11],
                  [30.54, 50.42],
                  [26.74, 58.36],
                  [17.13, 51.11]
                ]
               ],
              [
                [
                  [19.84, 41.33],
                  [30.45, 49.26],
                  [17.07, 50.10],
                  [19.84, 41.33]
                ]
              ]
           ]
       }

  it is converted to a QVariantMap with the following structure:

       {
         type : "MultiPolygon"
         data : [
           {
             type : "Polygon"
             data : QGeoPolygon([{51.110, 17.130}, {50.420,30.540}, {58.360, 26.700}, {51.110, 17.130}])
           },
           {
             type : "Polygon"
             data : QGeoPolygon([{41.330, 19.840}, {49.260,30.450}, {50.100, 17.070}, {41.330, 19.840}])
           }
         ]
       }

The `GeometryCollection` is a heterogeneous composition of other geometry types. In the resulting QVariantMap, the value of the `data` member is a QVariantList populated by QVariantMaps of various geometries, including the GeometryCollection itself.

For example, the following `GeometryCollection`:

     {
         "type" : "GeometryCollection",
         "geometries" : [
             {
                 "type" : "MultiPoint",
                 "coordinates" : [
                   [11,60], [5.5,60.3], [5.7,58.90]
                 ]
             },
             {
                 "type" : "MultiLineString",
                 "coordinates" : [
                   [[13.5, 43], [10.73, 59.92]],
                   [[9.15, 45], [-3.15, 58.90]]
                 ]
             },
             {
                 "type" : "MultiPolygon",
                 "coordinates" : [
                     [
                       [[17.13, 51.11],
                        [30.54, 50.42],
                        [26.74, 58.36],
                        [17.13, 51.11]]
                     ],
                     [
                       [[19.84, 41.33],
                        [30.45, 49.26],
                        [17.07, 50.10],
                        [19.84, 41.33]]
                     ]
                 ]
             }
         ]
     }

it is converted to a QVariantMap with the following structure:

     {
       type : "GeometryCollection"
       data : [
         {
           type : "MultiPolygon"
           data : [
             {
               type : "Polygon"
               data : QGeoPolygon([{41.330, 19.840}, {49.260, 30.450}, {50.100, 17.070}, {41.330, 19.840}])
             }
             {
               type : "Polygon"
               data : QGeoPolygon([{51.110, 17.130}, {50.420, 30.540}, {58.360, 26.740}, {51.110, 17.130}])
             }
           ]
         }
         {
           type : "MultiLineString"
           data : [
             {
               type : "LineString"
               data : QGeoPath([{45.000, 9.150}, {58.900, -3.150}])
             }
             {
               type : "LineString"
               data : QGeoPath([{43.000, 13.500}, {59.920, 10.730}])
             }
           ]
         }
         {
           type : "MultiPoint"
           data : [
             {
               type : Point
               data : QGeoCircle({58.900, 5.700}, -1)
             },
             {
               type : Point
               data : QGeoCircle({60.300, 5.500}, -1)
             },
             {
               type : Point
               data : QGeoCircle({60.000, 11.000}, -1)
             }
           ]
         }
       ]
     }

The `Feature` object, which consists of one of the previous geometries together with related attributes, is structured like one of the 7 above mentioned geometry types, plus a `properties` member. The value of this member is a QVariantMap. The only way to distinguish a Feature from the included geometry is to check if a `properties` node is present in the QVariantMap.

For example, the following `Feature`:

     {
         "type" : "Feature",
         "id" : "Poly",
         "properties" : {
             "text" : "This is a Feature with a Polygon"
         },
         "geometry" : {
             "type" : "Polygon",
             "coordinates" : [
                 [[17.13, 51.11],
                  [30.54, 50.42],
                  [26.70, 58.36],
                  [17.13, 51.11]],
                 [[23.46, 54.36],
                  [20.52, 51.91],
                  [28.25, 51.50],
                  [26.80, 54.36],
                  [23.46, 54.36]]
             ]
         }
     }

it is converted to a QVariantMap with the following structure:

     {
       type : "Polygon"
       data : QGeoPolygon([{51.110, 17.130}, {50.420,30.540}, {58.360, 26.700}, {51.110, 17.130}])
       properties : {text : "This is a Feature with a Polygon"}
     }

The `FeatureCollection` is a composition of Feature objects. The value of the `data` member in a FeatureCollection is a QVariantList populated by Feature type QVariantMaps.

For example, the following `FeatureCollection`:

     {
         "type" : "FeatureCollection",
         "features" : [
             {
                 "type" : "Feature",
                 "id" : "Poly",
                 "properties" : {
                     "text" : "This is a Feature with a Polygon"
                 },
                 "geometry" : {
                    "type" : "Polygon",
                    "coordinates" : [
                       [[17.13, 51.11],
                        [30.54, 50.42],
                        [26.70, 58.36],
                        [17.13, 51.11]],
                       [[23.46, 54.36],
                        [20.52, 51.91],
                        [28.25, 51.50],
                        [26.80, 54.36],
                        [23.46, 54.36]]
                    ]
                }
            },
            {
                "type" : "Feature",
                "id" : "MultiLine",
                "properties" : {
                    "text" : "This is a Feature with a MultiLineString"
                },
                "geometry" : {
                   "type" : "MultiLineString",
                   "coordinates" : [
                     [[13.5, 43], [10.73, 59.92]],
                     [[9.15, 45], [-3.15, 58.90]]
                   ]
                }
            }
         ]
     }

it is converted to a QVariantMap with the following structure:

     {
       type : "FeatureCollection"
       data : [
         {
           type : "MultiLineString"
           data : [
             {
               type : "LineString"
               data : QGeoPath([{45.000, 9.150}, {58.900, -3.150}])
             }
             {
               type : "LineString"
               data : QGeoPath([{43.000, 13.500}, {59.920, 10.730}])
             }
           ]
           properties : {text : "This is a Feature with a MultiLineString"}
         },
         {
           type : "Polygon"
           data : QGeoPolygon({51.110, 17.130}, {50.420, 30.540}, {58.360, 26.700}, {51.110, 17.130})
           properties : {text : "This is a Feature with a Polygon"}
         }
       ]
     }

#### Exporting GeoJSON

The exporter accepts the QVariantList returned by the importer, and returns a JSON document. The exporter is complementary to the importer because it executes the inverse action.

#### The toString function

The toString outputs, for debugging purposes, the content of a QVariantList structured like importGeoJson does, to a QString using a prettyfied format.

## Function Documentation

### QJsonDocument QGeoJson::exportGeoJson(const QVariantList &geoData)

This method exports the QVariantList geoData, expected to be structured like described in the section Importing GeoJSON, to a QJsonDocument containing the data converted to GeoJSON.

Note: This method performs no validation on the input.

See also importGeoJson.

### QVariantList QGeoJson::importGeoJson(const QJsonDocument &geoJson)

This method imports the geoJson document, expected to contain valid GeoJSON data, into a QVariantList structured like described in the section Importing GeoJSON.

Note: This method performs no validation on the input.

See also exportGeoJson.

### QString QGeoJson::toString(const QVariantList &geoData)

This method accepts the QVariantList geoData, structured as described in Importing GeoJSON, and returns a string containing the same data in a readable form.