QGeoJson Class
Header: | #include <QGeoJson> |
qmake: | QT += location |
Since: | Qt 5.13 |
This class was introduced in Qt 5.13.
Static Public Members
QJsonDocument | exportGeoJson(const QVariantList &geoData) |
QVariantList | importGeoJson(const QJsonDocument &geoJson) |
QString | toString(const QVariantList &geoData) |
Detailed Description
QGeoJson class 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. WARNING! 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, since 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 this node. 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 ia 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" : "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) } ] }
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.
Member Function Documentation
[static]
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.
[static]
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.
[static]
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.