2011.01.27 11:16

Introduction

There are 3 network providers in Android (ranging from 1.5 to 2.2). They are:

  1. gps –> (GPS, AGPS) 
    Name of the GPS location provider. This provider determines location using satellites. Depending on conditions, this provider may take a while to return a location fix. Requires the permission android.permission.ACCESS_FINE_LOCATION.
  2. network –> (AGPS, CellID, WiFi MACID) 
    Name of the network location provider. This provider determines location based on availability of cell tower and WiFi access points. Results are retrieved by means of a network lookup. Requires either of the permissions android.permission.ACCESS_COARSE_LOCATION or android.permission.ACCESS_FINE_LOCATION.
  3. passive –> (CellID, WiFi MACID) 
    A special location provider for receiving locations without actually initiating a location fix. This provider can be used to passively receive location updates when other applications or services request them without actually requesting the locations yourself. This provider will return locations generated by other providers. Requires the permission android.permission.ACCESS_FINE_LOCATION, although if the GPS is not enabled this provider might only return coarse fixes.

This is what Android calls these location providers, however, the underlying technologies to make this stuff work is mapped to the specific set of hardware and telco provided capabilities (network service).

Here is a table that maps/lists the underlying technologies in a different way:

Accuracy

Power Usage

Technology

20ft

High

Autonomous GPS, Provider: gps

  1. uses GPS chip on the device
  2. line of sight to the satellites
  3. need about 7 to get a fix
  4. takes a long time to get a fix
  5. doesn’t work around tall buildings

200ft

Medium – Low

Assisted GPS (AGPS), Provider: network

  1. uses GPS chip on device, as well as assistance from the network (cellular network) to provide a fast initial fix
  2. very low power consumption
  3. very accurate
  4. works without any line of sight to the sky
  5. depends on carrier and phone supporting this (even if phone supports it, and network does not then this does not work)

5300ft / 1mile

Low

CellID lookup/WiFi MACID lookup, Provider: network or passive

  1. very fast lock, and does not require GPS chip on device to be active
  2. requires no extra power at all
  3. has very low accuracy; sometimes can have better accuracy in populated and well mapped areas that have a lot of WiFi access points, and people who share their location with Google

Android layers these underlying techniques and technologies into the 3 network providers listed above. There is no good way know exactly what Android will use, since all phones are different. Eg, on VZW network, the LG Ally does NOT have AGPS! The Droid 2 has all providers (AGPS, GPS, CellID, etc). On ATT network, almost all phones tend to have AGPS enabled by default, etc. Varies by network, by coverage area, and by country, and by device. Also, on VZW, the passive provider ends up using Verizon Location Services, which are very inaccurate (less accurate than 1 mile).


Summary

The best way to handle GPS is to use the “network” or “passive” provider first, and then fallback on “gps”, and depending on the task, switch between providers. This covers all cases, and provides a lowest common denominator service (in the worst case) and great service (in the best case).


copy - ScreamingToaster LLC  

thank you!

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