The Map type allows the display of a map and placing objects within the map. Various points of interest can be defined and added to the map for display. Also the Map has features to control how the map is displayed. With the Map item you can center the map, zoom, pinch and make the item flickable.
The places to be added to the map are MapItems . The item's position is defined by a coordinate which includes latitude, longitude and altitude. The item is then displayed automatically after it is added to the Map .
All position APIs are part of the QtPositioning module. The basic piece of position information is the coordinate . A coordinate encapsulates data for the latitude, longitude and altitude of the location. Altitude is in meters. It also has a method to determine distance to another coordinate 。 coordinate type may also be held within a 定位 element, this will also have information on a bounding box size to determine sufficient proximity to the location and a location address.
Here is an example of a client that uses a position source to center a map on the current position:
Rectangle {
import QtPositioning 5.2
import QtLocation 5.3
...
Map {
id: map
// initialize map
...
}
PositionSource {
onPositionChanged: {
// center the map on the current position
map.center = position.coordinate
}
}
}
Geocoding is the derivation of geographical coordinates (latitude and longitude) from other geographical references to the locations. For example, this can be a street address. Reverse geocoding is also possible with a street address being used to determine a geographical coordinate. Geocoding is performed by using the GeocodeModel 类型。
The following code examples are a small part of the
map
component in the
地图查看器 (QML)
example. The snippets demonstrate the declaration of the
GeocodeModel
组件。
In the snippet we see that the [QML]{
GeocodeModel
} contains the plugin and two signal handlers. One for changes in status
onStatusChanged
and the other to update the centering of the Map object
onLocationsChanged
.
GeocodeModel { id: geocodeModel plugin: map.plugin onStatusChanged: { if ((status == GeocodeModel.Ready) || (status == GeocodeModel.Error)) map.geocodeFinished() } onLocationsChanged: { if (count == 1) { map.center.latitude = get(0).coordinate.latitude map.center.longitude = get(0).coordinate.longitude } } } MapItemView { model: geocodeModel delegate: pointDelegate }
The geocoding features are called from a higher level piece of code. In this snippet we see an 地址 object filled with the desired parameters.
Address { id :fromAddress street: "Sandakerveien 116" city: "Oslo" country: "Norway" state : "" postalCode: "0484" }
The 地址 is later used in a query for the GeocodeModel to process and determine the geographical coordinates .
// send the geocode request geocodeModel.query = fromAddress geocodeModel.update()
A very important function of the Map type is navigation from one place to a destination with possible waypoints along the route. The route will be divided up into a series of segments. At the end of each segment is a vertex called a maneuver 。 segments contain information about the time and distance to the end of the segment. The maneuvers contain information about what to do next, how to get onto the next segment, if there is one. So a maneuver contains navigational information, for example "turn right now".
To find a suitable route we will need to use a RouteQuery to define the selection criteria and adding any required waypoints. The RouteModel should return a list of RouteSegment s that defines the route to the destination complete with navigation advice at the joins between segments, called RouteManeuver s
There are many options that you can add to the query to narrow the criteria. The RouteQuery properties can include
| numberAlternativeRoutes | The number of alternative routes |
| travelModes | Travel modes |
| routeOptimizations | Required route optimizations |
| segmentDetail | Level of detail in segments |
| maneuverDetail | Level of detail in maneuvers between segments |
| waypoints | A list of waypoints |
| excludedAreas | A list of excluded areas that the route must not cross |
| featureTypes | Relevant map features, for example highway, ferry |
In the following example a default RouteQuery is declared within RouteModel .
RouteModel { id: routeModel plugin : map.plugin query: RouteQuery { id: routeQuery } onStatusChanged: { if (status == RouteModel.Ready) { switch (count) { case 0: // technically not an error map.routeError() break case 1: map.showRouteList() break } } else if (status == RouteModel.Error) { map.routeError() } } }
The user enters some information such as the starting point of the route, some waypoints and the destination. All of these locations are waypoints so the locations from start to finish will be entered as a sequence of waypoints. Then other query properties can be set that may be specific to this trip.
// clear away any old data in the query routeQuery.clearWaypoints(); // add the start and end coords as waypoints on the route routeQuery.addWaypoint(startCoordinate) routeQuery.addWaypoint(endCoordinate) routeQuery.travelModes = RouteQuery.CarTravel routeQuery.routeOptimizations = RouteQuery.FastestRoute routeModel.update();
The
routeInfoModel
ListModel
is used to grab the results of the query and construct a suitable list for display.
ListView { interactive: true model: ListModel { id: routeInfoModel } header: RouteListHeader {} delegate: RouteListDelegate{ routeIndex.text: index + 1 routeInstruction.text: instruction routeDistance.text: distance } }
The
ListModel
routeInfoModel
can be filled with values using a code, that loops through the segments extracting the segment length, instruction text and distance to the next instruction. The extracted data is formatted for display as it is retrieved.
routeInfoModel.clear() if (routeModel.count > 0) { for (var i = 0; i < routeModel.get(0).segments.length; i++) { routeInfoModel.append({ "instruction": routeModel.get(0).segments[i].maneuver.instructionText, "distance": Helper.formatDistance(routeModel.get(0).segments[i].maneuver.distanceToNextInstruction) }); } }
For more information on the example see the 地图查看器 (QML) 范例。
The Map item also supports user interface interactions with the map using tactile and mouse gestures. That is features such as swiping to pan, pinching to zoom.
Enabling and configuring pinch and flickable is easy within the Map 类型。
Map { id: map // Enable pan, flick, and pinch gestures to zoom in and out gesture.acceptedGestures: MapGestureArea.PanGesture | MapGestureArea.FlickGesture | MapGestureArea.PinchGesture | MapGestureArea.RotationGesture | MapGestureArea.TiltGesture gesture.flickDeceleration: 3000 gesture.enabled: true }
Zoom can also be controlled by other objects like sliders, with binding to the Map zoomLevel .
| Type provides support for searching operations related to geographic information |
The above snippets are taken from the 地图查看器 (QML) 范例。