1# Location Service Development 2 3## Overview 4 5People take their mobile devices wherever they go. Mobile devices have become a necessity in people's daily routines, whether it be for looking at the weather forecast, browsing news, hailing a taxi, navigating, or recording data from a workout. All these activities are so much associated with the location services on mobile devices. 6 7With the location awareness capability offered by OpenHarmony, mobile devices will be able to obtain real-time, accurate location data. Building location awareness into your application can also lead to a better contextual experience for application users. 8 9Your application can call location-specific APIs to obtain the location information of a mobile device for offering location-based services such as drive navigation and motion track recording. 10 11### Service Introduction 12 13Location awareness helps determine where a mobile device locates. The location subsystem identifies the location of a mobile device with its coordinates, and uses location technologies such as Global Navigation Satellite System (GNSS) and network positioning (for example, base station positioning or WLAN/Bluetooth positioning) to provide diverse location-based services. 14 15These advanced location technologies make it possible to obtain the accurate location of the mobile device, regardless of whether it is indoors or outdoors. 16 17- **Coordinate** 18 19 A coordinate describes a location on the earth using the longitude and latitude in reference to the World Geodetic Coordinate System 1984. 20 21- **GNSS positioning** 22 23 GNSS positioning locates a mobile device by using the location algorithm offered by the device chip to compute the location information provided by the Global Navigation Satellite System, for example, GPS, GLONASS, BeiDou, and Galileo. Whichever positioning system will be used during the location process depends on a hardware capability of the device. 24 25- **Base station positioning** 26 27 Base station positioning estimates the current location of a mobile device based on the location of the resident base station in reference to the neighboring base stations. This technology provides only a low accuracy and requires access to the cellular network. 28 29- **WLAN or Bluetooth positioning** 30 31 WLAN or Bluetooth positioning estimates the current location of a mobile device based on the locations of WLANs and Bluetooth devices that can be discovered by the device. The location accuracy of this technology depends on the distribution of fixed WLAN access points (APs) and Bluetooth devices around the device. A high density of WLAN APs and Bluetooth devices can produce a more accurate location result than base station positioning. This technology also requires access to the network. 32 33### Working Principles 34 35Location awareness is offered by the system as a basic service for applications. Depending on the service scenario, an application needs to initiate a location request to the system and stop the location request when the service scenario ends. In this process, the system reports the location information to the application on a real-time basis. 36 37### Constraints 38 39Your application can use the location function only after the user has granted the required permission and turned on the location function. If the location function is off, the system will not provide the location service for any application. 40 41Since the location information is considered sensitive, your application still needs to obtain the location access permission from the user even if the user has turned on the location function. The system will provide the location service for your application only after it has been granted the permission to access the device location information. 42 43 44## Applying for Location Permissions 45 46### When to Use 47 48Before using system basic location capabilities, check whether your application has been granted the permission to access the device location information. If not, your application needs to obtain the permission from the user. 49 50The system provides the following location permissions: 51 52- ohos.permission.LOCATION: used to obtain location accurate to meters. 53 54- ohos.permission.APPROXIMATELY\_LOCATION: used to obtain location accurate to 5 kilometers. 55 56- ohos.permission.LOCATION\_IN\_BACKGROUND: used to obtain location while the application is running at the background. 57 58If your application needs to access the device location information, it must first apply for required permissions. 59 60**Table 1** Ways to apply for location permissions 61 62| Target API Level| Location Permission| Permission Application Result| Location Accuracy| 63| -------- | -------- | -------- | -------- | 64| Earlier than 9| ohos.permission.LOCATION | Successful| Location accurate to meters.| 65| 9 and later| ohos.permission.LOCATION | Failed| No location obtained.| 66| 9 and later| ohos.permission.APPROXIMATELY_LOCATION | Successful| Location accurate to 5 kilometers.| 67| 9 and later| ohos.permission.APPROXIMATELY_LOCATION and ohos.permission.LOCATION| Successful| Location accurate to meters.| 68 69If your application needs to access the device location information when running in the background, it must be configured to be able to run in the background and be granted the **ohos.permission.LOCATION_IN_BACKGROUND** permission. In this way, the system continues to report device location information after your application moves to the background. 70 71You can declare the required permission in your application's configuration file. For details, see [Access Control (Permission) Development](../security/accesstoken-guidelines.md). 72 73For details about the permissions required for each API of the location service, see [Geolocation Manager](../reference/apis/js-apis-geoLocationManager.md). 74 75### How to Develop 76 77You can declare the required permission in your application's configuration file. For details, see [Access Control (Permission) Development](../security/accesstoken-guidelines.md). 78 79 80## Obtaining Device Location Information 81 82### When to Use 83 84You can call location-related APIs in OpenHarmony to obtain the real-time location or last known location of a mobile device. 85 86Real-time location of the device is recommended for location-sensitive services. If you want to lower power consumption when the real-time location of the device is not needed, you may consider obtaining the last known location of the device. 87 88### Available APIs 89 90The following table lists the APIs used to obtain the device location information. For details, see [Geolocation Manager](../reference/apis/js-apis-geoLocationManager.md). 91 92**Table 2** APIs for obtaining device location information 93 94| API| Description| 95| -------- | -------- | 96| on(type: 'locationChange', request: LocationRequest, callback: Callback<Location>): void | Registers a listener for location changes with a location request initiated.| 97| off(type: 'locationChange', callback?: Callback<Location>): void | Unregisters the listener for location changes with the corresponding location request deleted.| 98| getCurrentLocation(request: CurrentLocationRequest, callback: AsyncCallback<Location>): void | Obtains the current location. This API uses an asynchronous callback to return the result. | 99| getCurrentLocation(request?: CurrentLocationRequest): Promise<Location> | Obtains the current location. This API uses a promise to return the result. | 100| getLastLocation(): Location | Obtains the last known device location.| 101 102### How to Develop 103 1041. Before using basic location capabilities, check whether your application has been granted the permission to access device location information. If not, your application first needs to apply for the required permission. For details, see [Applying for Location Permissions](#applying-for-location-permissions). 105 1062. Import the **geoLocationManager** module by which you can implement all APIs related to the basic location capabilities. 107 108 ```ts 109 import geoLocationManager from '@ohos.geoLocationManager'; 110 ``` 111 1123. Instantiate the **LocationRequest** object. This object provides APIs to notify the system of the location service type and the interval of reporting location information.<br> 113 **Method 1:** 114 115 To better serve your needs for using APIs, the system has categorized APIs into different packages to match your common use cases of the location function. In this way, you can directly use the APIs specific to a certain use case, making application development much easier. The location service scenarios currently supported are described as follows. 116 117 **Location service scenarios** 118 119 - NAVIGATION<br> 120 Applicable when your application needs to obtain the real-time location of a mobile device outdoors, such as navigation for driving or walking. <br>In this scenario, the GNSS positioning technology is mainly used to ensure the location accuracy. However, due to its limitations, the technology may be unable to provide the location service when navigation is just started or when the user moves into a shielded environment such as indoors or a garage. <br>To resolve this issue, the system uses the network positioning technology as an alternative to provide the location service for your application until the GNSS can provide stable location results. This helps achieve a smooth navigation experience for users. <br>By default, the system reports location results at a minimal interval of 1s. To adopt this use case, you must declare the **ohos.permission.LOCATION** permission and obtain users' authorization. 121 122 - TRAJECTORY\_TRACKING<br> 123 Applicable when your application needs to record user trajectories, for example, the track recording function of sports applications. In this scenario, the GNSS positioning technology is mainly used to ensure the location accuracy. <br>By default, the system reports location results at a minimal interval of 1s. To adopt this use case, you must declare the **ohos.permission.LOCATION** permission and obtain users' authorization. 124 125 - CAR\_HAILING<br> 126 Applicable when your application needs to obtain the current location of a user who is hailing a taxi. <br>By default, the system reports location results at a minimal interval of 1s. To adopt this use case, you must declare the **ohos.permission.LOCATION** permission and obtain users' authorization. 127 128 - DAILY\_LIFE\_SERVICE<br> 129 Applicable when your application only needs the approximate user location for recommendations and push notifications in scenarios such as when the user is browsing news, shopping online, and ordering food. <br>By default, the system reports location results at a minimal interval of 1s. To adopt this use case, you must declare the **ohos.permission.LOCATION** permission and obtain users' authorization. 130 131 - NO\_POWER<br> 132 Applicable when your application does not proactively start the location service for a higher battery efficiency. When responding to another application requesting the same location service, the system marks a copy of the location result to your application. In this way, your application will not consume extra power for obtaining the user location. <br>By default, the system reports location results at a minimal interval of 1s. To adopt this use case, you must declare the **ohos.permission.LOCATION** permission and obtain users' authorization. 133 134 135 ```ts 136 export enum LocationRequestScenario { 137 UNSET = 0x300, 138 NAVIGATION, 139 TRAJECTORY_TRACKING, 140 CAR_HAILING, 141 DAILY_LIFE_SERVICE, 142 NO_POWER, 143 } 144 ``` 145 146 147Sample code for initializing **requestInfo** for navigation: 148 149 ```ts 150 let requestInfo = {'scenario': geoLocationManager.LocationRequestScenario.NAVIGATION, 'timeInterval': 0, 'distanceInterval': 0, 'maxAccuracy': 0}; 151 ``` 152 153**Method 2:** 154 155If the predefined use cases do not meet your needs, you can also use the basic location priority policies provided by the system. 156 157 **Location priority policies** 158 159 - ACCURACY<br> 160 This policy mainly uses the GNSS positioning technology. In an open area, the technology can achieve the meter-level location accuracy, depending on the hardware performance of the device. However, in a shielded environment, the location accuracy may significantly decrease. 161 162 - FIRST\_FIX<br> 163 This policy uses the GNSS positioning, base station positioning, WLAN positioning, and Bluetooth positioning technologies simultaneously to obtain the device location in both the indoor and outdoor scenarios. When all positioning technologies provide a location result, the system provides the most accurate location result for your application. This policy can lead to significant hardware resource consumption and power consumption. 164 165 - LOW\_POWER<br> 166 This policy mainly uses the base station positioning, WLAN positioning, and Bluetooth positioning technologies to obtain device location in both indoor and outdoor scenarios. The location accuracy depends on the distribution of surrounding base stations, visible WLANs, and Bluetooth devices and therefore may fluctuate greatly. This policy is recommended and can reduce power consumption when your application does not require high location accuracy or when base stations, visible WLANs, and Bluetooth devices are densely distributed. 167 168 ```ts 169 export enum LocationRequestPriority { 170 UNSET = 0x200, 171 ACCURACY, 172 LOW_POWER, 173 FIRST_FIX, 174 } 175 ``` 176 177Sample code for initializing **requestInfo** for the location accuracy priority policy: 178 179 ```ts 180 let requestInfo = {'priority': geoLocationManager.LocationRequestPriority.ACCURACY, 'timeInterval': 0, 'distanceInterval': 0, 'maxAccuracy': 0}; 181 ``` 182 1834. Instantiate the **Callback** object for the system to report location results. 184 Your application needs to implement the callback defined by the system. When the system successfully obtains the real-time location of a device, it will report the location result to your application through the callback interface. Your application can implement the callback interface in such a way to complete your own service logic. 185 186 ```ts 187 let locationChange = (location) => { 188 console.log('locationChanger: data: ' + JSON.stringify(location)); 189 }; 190 ``` 191 1925. Start obtaining the device location. 193 194 ```ts 195 geoLocationManager.on('locationChange', requestInfo, locationChange); 196 ``` 197 1986. (Optional) Stop obtaining the device location. 199 200 If your application no longer needs the device location, stop obtaining the device location to avoid high power consumption. 201 202 ```ts 203 geoLocationManager.off('locationChange', locationChange); 204 ``` 205 206 If your application does not need the real-time device location, it can use the last known device location cached in the system instead. 207 208 ```ts 209 import geoLocationManager from '@ohos.geoLocationManager'; 210 try { 211 let location = geoLocationManager.getLastLocation(); 212 } catch (err) { 213 console.error("errCode:" + err.code + ",errMessage:" + err.message); 214 } 215 ``` 216 217 218## Geocoding and Reverse Geocoding 219 220### When to Use 221 222Describing a location using coordinates is accurate, but neither intuitive nor user-friendly. To address this issue, the system provides your application the geocoding and reverse geocoding capabilities: 223 224- Geocoding: converts geographic descriptions into specific coordinates. 225 226- Reverse geocoding: converts coordinates into geographic descriptions. 227 228The geocoding information describes a location using several attributes, including the country, administrative region, street, house number, and address, etc. 229 230### Available APIs 231 232The following table lists the APIs used for mutual conversion between coordinates and geographic descriptions. For details, see [Geolocation Manager](../reference/apis/js-apis-geoLocationManager.md). 233 234**Table 3** APIs for geocoding and reverse geocoding conversion 235 236| API| Description| 237| -------- | -------- | 238| isGeocoderAvailable(): boolean; | Obtains the (reverse) geocoding service status.| 239| getAddressesFromLocation(request: ReverseGeoCodeRequest, callback: AsyncCallback<Array<GeoAddress>>): void | Converts coordinates into geographic descriptions through reverse geocoding. This API uses an asynchronous callback to return the result. | 240| getAddressesFromLocation(request: ReverseGeoCodeRequest): Promise<Array<GeoAddress>> | Converts coordinates into geographic descriptions through reverse geocoding. This API uses a promise to return the result. | 241| getAddressesFromLocationName(request: GeoCodeRequest, callback: AsyncCallback<Array<GeoAddress>>): void | Converts geographic descriptions into coordinates through geocoding. This API uses an asynchronous callback to return the result. | 242| getAddressesFromLocationName(request: GeoCodeRequest): Promise<Array<GeoAddress>> | Converts geographic descriptions into coordinates through geocoding. This API uses a promise to return the result. | 243 244### How to Develop 245 246> **NOTE** 247> 248> The **GeoConvert** instance needs to access backend services to obtain information. Therefore, before performing the following steps, ensure that your device is connected to the network. 249 2501. Import the **geoLocationManager** module by which you can implement all APIs related to the geocoding and reverse geocoding conversion capabilities. 251 252 ```ts 253 import geoLocationManager from '@ohos.geoLocationManager'; 254 ``` 255 2562. Check whether the **geoCoder** service is available. 257 258 Call **isGeoServiceAvailable** to check whether the **geoCoder** service is available. If the service is available, go to step 3. 259 260 ```ts 261 import geoLocationManager from '@ohos.geoLocationManager'; 262 try { 263 let isAvailable = geoLocationManager.isGeocoderAvailable(); 264 } catch (err) { 265 console.error("errCode:" + err.code + ",errMessage:" + err.message); 266 } 267 ``` 268 2693. Obtain the geocoding conversion result. 270 - Call **getAddressesFromLocation** to convert coordinates into geographical location information. 271 272 ```ts 273 let reverseGeocodeRequest = {"latitude": 31.12, "longitude": 121.11, "maxItems": 1}; 274 try { 275 geoLocationManager.getAddressesFromLocation(reverseGeocodeRequest, (err, data) => { 276 if (err) { 277 console.log('getAddressesFromLocation err: ' + JSON.stringify(err)); 278 } else { 279 console.log('getAddressesFromLocation data: ' + JSON.stringify(data)); 280 } 281 }); 282 } catch (err) { 283 console.error("errCode:" + err.code + ",errMessage:" + err.message); 284 } 285 ``` 286 287 The application can access the **GeoAddress** list that matches the specified coordinates for the corresponding geographic descriptions. For details, see [Geolocation Manager](../reference/apis/js-apis-geoLocationManager.md). 288 - Call **getAddressesFromLocationName** to convert geographic descriptions into coordinates. 289 290 ```ts 291 let geocodeRequest = {"description": "No. xx, xx Road, Pudong District, Shanghai", "maxItems": 1}; 292 try { 293 geoLocationManager.getAddressesFromLocationName(geocodeRequest, (err, data) => { 294 if (err) { 295 console.log('getAddressesFromLocationName err: ' + JSON.stringify(err)); 296 } else { 297 console.log('getAddressesFromLocationName data: ' + JSON.stringify(data)); 298 } 299 }); 300 } catch (err) { 301 console.error("errCode:" + err.code + ",errMessage:" + err.message); 302 } 303 ``` 304 305 The application can access the **GeoAddress** list that matches the specified geographic descriptions for the corresponding coordinates. For details, see [Geolocation Manager](../reference/apis/js-apis-geoLocationManager.md). 306 307 To improve the accuracy of location results, you can set the longitude and latitude ranges in **GeoCodeRequest**. 308 309 310## Geofencing 311 312### When to Use 313 314A geofence is a group of virtual bounds defining an area on the map. When a user device enters or leaves a geofence, or stays in a geofence, your app on the user device can automatically receive notifications and alarms. 315 316Currently, only circular geofences are supported, and the geofencing function of the GNSS chip is required. 317 318A typical application of geofencing is to create a geofence around an enterprise for targeted advertising. In different areas, you can provide differentiated promotions for mobile devices. 319 320### Available APIs 321 322The following table lists the APIs used for geofencing. For details, see [Geolocation Manager](../reference/apis/js-apis-geoLocationManager.md). 323 324**Table 4** Geofencing APIs 325 326| API| Description| 327| -------- | -------- | 328| on(type: 'gnssFenceStatusChange', request: GeofenceRequest, want: WantAgent): void; | Registers a listener for status change events of the specified geofence.| 329| off(type: 'gnssFenceStatusChange', request: GeofenceRequest, want: WantAgent): void; | Unregisters the listener for status change events of the specified geofence.| 330 331### How to Develop 332 3331. Declare the **ohos.permission.APPROXIMATELY_LOCATION** permission. For details, see [Applying for Location Permissions](#applying-for-location-permissions). 334 3352. Import the [geoLocationManager](../reference/apis/js-apis-geoLocationManager.md) and [wantAgent](../reference/apis/js-apis-app-ability-wantAgent.md) modules. 336 337 ```ts 338 import geoLocationManager from '@ohos.geoLocationManager'; 339 import wantAgent from '@ohos.app.ability.wantAgent'; 340 ``` 341 3423. Create a [WantAgentInfo](../reference/apis/js-apis-inner-wantAgent-wantAgentInfo.md) object. 343 344 Scenario 1: Create a **WantAgentInfo** object for starting an ability. 345 346 ```ts 347 let wantAgentObj = null; // Save the created WantAgent object for completing the trigger operations at a later time. 348 349 // Set the operation type through operationType of the WantAgentInfo object. 350 let wantAgentInfo = { 351 wants: [ 352 { 353 deviceId: '', 354 bundleName: 'com.example.myapplication', 355 abilityName: 'EntryAbility', 356 action: '', 357 entities: [], 358 uri: '', 359 parameters: {} 360 } 361 ], 362 operationType: wantAgent.OperationType.START_ABILITY, 363 requestCode: 0, 364 wantAgentFlags:[wantAgent.WantAgentFlags.CONSTANT_FLAG] 365 }; 366 ``` 367 368 Scenario 2: Create a **WantAgentInfo** object for publishing [common events](../application-models/common-event-overview.md). 369 370 ```ts 371 let wantAgentObj = null; // Save the created WantAgent object for completing the trigger operations at a later time. 372 373 // Set the operation type through operationType of the WantAgentInfo object. 374 let wantAgentInfo = { 375 wants: [ 376 { 377 action: "event_name", // Set the event name. 378 parameters: {}, 379 } 380 ], 381 operationType: wantAgent.OperationType.SEND_COMMON_EVENT, 382 requestCode: 0, 383 wantAgentFlags: [wantAgent.WantAgentFlags.CONSTANT_FLAG], 384 } 385 ``` 386 3874. Call [getWantAgent()](../reference/apis/js-apis-app-ability-wantAgent.md#wantagentgetwantagent) to create a **WantAgent** object. 388 389 After obtaining the **WantAgent** object, call the geofencing API to add a geofence. 390 391 ```ts 392 // Create a WantAgent object. 393 wantAgent.getWantAgent(wantAgentInfo, (err, data) => { 394 if (err) { 395 console.error('getWantAgent err=' + JSON.stringify(err)); 396 return; 397 } 398 console.info('getWantAgent success'); 399 wantAgentObj = data; 400 let requestInfo = {'priority': 0x201, 'scenario': 0x301, "geofence": {"latitude": 121, "longitude": 26, "radius": 100, "expiration": 10000}}; 401 try { 402 geoLocationManager.on('gnssFenceStatusChange', requestInfo, wantAgentObj); 403 } catch (err) { 404 console.error("errCode:" + err.code + ",errMessage:" + err.message); 405 } 406 }); 407 ``` 408 4095. Have the system automatically trigger the action defined for the **WantAgent** object when a device enters or exits the geofence.