PSLab Android app is an open source app that uses fully open libraries and tools so that the community can use all it’s features without any compromises related to pricing or feature constraints. This will brings us to the topic how to implement a map feature in PSLab Android app without using proprietary tools and libraries. This is really important as now the app is available on Fdroid and they don’t allow apps to have proprietary tools in them if they are published there. In other words, it simply says we cannot use Google Maps APIs no matter how powerful they are in usage.
There is a workaround and that is using Open Street Maps (OSM). OSM is an open source project which is supported by a number of developers all around the globe to develop an open source alternative to Google Maps. It supports plenty of features we need in PSLab Android app as well. Starting from displaying a high resolution map along with caching the places user has viewed, we can add markers to show data points and locations in sensor data logging implementations.
All these features can be made available once we add the following dependencies in gradle build file. Make sure to use the latest version as there will be improvements and bug fixes in each newer version
implementation "org.osmdroid:osmdroid-android:$rootProject.osmVersion" implementation "org.osmdroid:osmdroid-mapsforge:$rootProject.mapsforgeVersion" implementation "org.osmdroid:osmdroid-geopackage:$rootProject.geoPackageVersion"
OSM will be functional only after the following permission states were granted.
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
In a view xml file, add the layout org.osmdroid.views.MapView to initiate the map view. There is a known issue in OSM library. That is during the initiation, if the zoom factor is set to a small value, there will be multiple instances of maps as shown in Fig 1. The solution is to have a higher zoom value when the map is loaded.
Figure 1: Multiple map tiles in OSM
Once we initialize the map view inside an activity, a zoom level can be easily set using a map controller as follows;
map = findViewById(R.id.osmmap); map.setTileSource(TileSourceFactory.MAPNIK); map.setBuiltInZoomControls(true); map.setMultiTouchControls(true); IMapController mapController = map.getController(); mapController.setZoom((double) 9); GeoPoint startPoint = new GeoPoint(0.00, 0.00); mapController.setCenter(startPoint);
After successfully implementing the map view, we can develop the business logic to add markers and descriptions to improve the usability of OS Maps. They will be available in the upcoming blog posts.
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