Android Tutorial [B4A] [B4XPages] OSM Maps / FusedLocationProviderClient GMS

May 4, 2024 - Start of tutorial post...

Based on:

Open Street Map viewer - GPS

Hi, This b4Xlib contains a custom view (cvMap) which can display Open Street Map. The tiles are retrieved from the internet and cached in a database. You can add shapes and images on the map. UI : - Lat/lng Center of the map - Zoom Level - Compass Direction with rotation - Scale - Button...

www.b4x.com

The original project was based on the GPS object / lib.. a power hungry outdated feature.
This example uses the latest "Fused" location provider (GMS) to accomplish the same... and more...

This tutorial shall evolve over a (short) time as discoveries are made clear to update / post. Hang in there...
This project also includes an app to feed MOCK locations (lat/lon/etc..) into the FusedLocationProvderGMS - to test your final distribution.

1) B4XPages
Although introduced long time ago - and evolved since then - this is my first introduction. (been busy sowing and harvesting my garden).
The first thing I notice is that B4A (pause and resume) complexities been (essentially) removed! Granted, there are some issues with Show and Hide ( show- B4XPages.ShowPage("destpag") hide - B4XPages.ShowPage("MainPage") but NOTHING that can't be overcome. It is all a matter of understanding what each does - and how each - PAGE - was implemented ( initialized / created / hidden).

For cross platform - (A,i,J), this IS a great leap forward. My focus shall be on B4A, for my ease of explanation...

All small Red Text are comments.
The Milepost Number and Milepost Name are GPS locations, derived form a SQLlite DB (lat/lon), that are either in front / or behind you depending on your travel direction.
There are much more intricacies to this project, but we shall leave it here for now until more can be defined in a clear and succinct manner.

 

[Harris]

Just as a background for the concept of this app...

The Dalton highway is 414 miles starting north of Fairbanks, AK and terminating at the Beaufort sea (in the Arctic -Prudhoe Bay - Deadhorse) - essentially is following the AK pipeline (north and south). This stretch of road (to my understanding) covers many different environments and elevations. These can pose - at any given time - an extreme challenge (wind, snow, fog) for anyone to comprehend to know (blinded) where they are currently at - and where they can safely pull off the road until visual conditions improve.

When this app is proved to be functional, it shall be released to users that can capture important "Points" OTHER THAN what DOT-AK has provided for each Mile Post marker. These are the road side pull outs - for semi's, material sites that can safely accommodate a rig, or any other location that can safely harbor a rig off the main road where other vehicles exist. When other vehicles are trapped within this envelope of blindness, they may (radio) communicate their exact location to warn others of their current location / proximity.

More to follow...

 

[Harris]

Fused Location Provider - GMS - Mock Location Provider App
​

When trying to develop a complex app utilizing Location / GPS functions, it is helpful to implement a method to 'Feed' data to 'simulate' progressive location (Lat / Lon) changes. Fortunately, the Android OS provides functionality to do this - in Development Mode.

<uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION" />
Apparently, the above line (in Manifest) defines 'This' app as a Mock Location Provider...

The Manifest of This app:

'This code will be applied to the manifest file during compilation.
'You do not need to modify it in most cases.
'See this link for for more information: https://www.b4x.com/forum/showthread.php?p=78136
AddManifestText(
<uses-sdk android:minSdkVersion="21" android:targetSdkVersion="33"/>
<uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION" />
<supports-screens android:largeScreens="true"
    android:normalScreens="true"
    android:smallScreens="true"
    android:anyDensity="true"/>)
SetApplicationAttribute(android:icon, "@drawable/icon")
SetApplicationAttribute(android:label, "$LABEL$")
CreateResourceFromFile(Macro, Themes.LightTheme)

AddManifestText(<uses-permission
    android:name="android.permission.WRITE_EXTERNAL_STORAGE"
    android:maxSdkVersion="19" />
)

CreateResourceFromFile(Macro, FirebaseAnalytics.GooglePlayBase)

'End of default text.

In Developer Options, (Android 9.0 +), we see a line to 'Set mock location app'.
I think, this is what the OS uses to determine which apps have the manifest android.permission.ACCESS_MOCK_LOCATION defined within - to allow to set / Feed MOCK.

When selecting this option, you choose which app will (potentially) provide MOCK locations - an app that overrides FLP from hardware (GPS chip) lat/lon values with ones that YOU inject (mock) into the underlying stack.
We choose the 'B4A FusedExample' (or whatever you rename it to).

Now, whenever this app is broadcasting: Fused.SetMockLocation( mlocation ), the OS will see this as the current LocationF object - (most importantly, lat / lon) and permit it to flow through to other Fused apps expecting this data.

Attention!
The Mock Location MUST be VALID to be accepted by the OS - in order to be passed on... This was my biggest struggle when getting this to work. What I found that it needs to be based on a "real" GPS location to start with, then you can inject / replace "other" lat/lon positions into the object - to allow the system to make it all look real...


WHOOP DE DO BASIL, BUT WHAT DOES IT ALL MEAN? IT SMELLS A BIT NUTTY.... (Austin Powers)

What I discovered was quite meaningful. Feeding mock locations allowed another system (using OSM) to 'Self Populate' a table within a DB to locally store the 'tiles' data required to accompany the (Visual Map) app - using (almost) FREE WIFI rather than EXPENSIVE Cell data plans to get the same data.... The only other way to get the Map Tiles is to Drive the Actual road (assuming it has cell service) to capture this data - WITHOUT resorting to downloading regional data from the (OSM - or other) map tile providers. Doing so can amount to MANY gigs of unwanted tiles (stored data) that you don't need. In my example, the map tile data amounted to more than 800 megabyte of REQUIRED storage to cover the 4 zoom levels provided within the app - for just ONE road (compared to many gig)!


NOTE:
For those of us wishing to EDIT this content, WARNING - Start a new thread ( don't EDIT / UPDATE ). I just did and LOST 1 hour that I must now repeat....

LIVE and LEARN... geeezzzz...
Will start again tomorrow, when I get my enthusiasm back... Thx.

 

[Harris]

Mock Location Provider App - continued...

This app is quite simple.
Open a table and get the UNIQUE route names from it (a unique column).
Init a Spinner with these values. Select ONE.

Determine ASC or DESC for table order (mile post number).
Set Mock Mode (ON or OFF)
Start feeding Mock Locations....

For each row, the mock location provider will inject the (New Record - Row) Lat / Lon into the system to simulate the current GPS position (using the valid GPS template).
This is where it can get a bit tricky. You need to establish a correct Fused GPS record (NO ?!?) fields in the LocationF object. This is why I hammer on the DefinedFused method to ensure we get one. Otherwise, MOCK will not work (feed these table locations). A clear view of the sky (NOT deep in your Mom's basement) is where you are most likely to get a valid GPS signal.

Image BEFORE Mock... (my current location)

Image AFTER Mock Enabled ... (Table Record current location). This will repeat a new position for each record in the table (every second).

As stated, this will allow you to build an OSM tile set without having to drive the actual road... - PROVIDING you have an accurate data set (Milepost Markers - lat/lon) to work from... The Alaska Department of Transportation did a superb job of recording this for my attempt to provide road users with a (free) system to keep everyone safe in time of need.