Before we can start developing, we first have to have a quick look at some of the existing technologies on the market today (this is by no means an exhaustive listing).

Accelerometer/Sensor Information and Profiled Path

• Good for metro only.
• Low accuracy.
• May require data connectivity.

Example:

http://grouplens.org/site-content/uploads/bhecht_sigspatial2014_subwayps.pdf

GPS Relay

• Can be very expensive to set up.
• Very accurate (depending on setup).

Example:

http://www.karstworlds.com/2011/01/underground-gps-finally-possible.html

• Can be expensive.
• Accuracy depends on implementation.

Example:

http://www.businesswire.com/news/home/20130819006343/en/Minetec-Partners-CSIRO-Deliver-Revolutionary-Underground-Positioning#.VQ7Sly5WJ-8

http://www.darpa.mil/Our_Work/STO/Programs/Adaptable_Navigation_Systems_%28ANS%29.aspx

Wi-Fi Positioning System

• Requires profiling of area (profiling can be inaccurate depending on factors such as time of day, changes over time).
• Requires data connectivity and database server.
• Medium accuracy.
• Widely used.
• Doesn't work where you cannot profile the access points against known positioning (GPS).

Example:

https://support.google.com/gmm/answer/1646140?hl=en
http://lens1.csie.ncku.edu.tw/Library/Paper/IEEE%20MDM%202009/data/3650a371.pdf

http://www.smh.com.au/digital-life/smartphone-apps/indoor-gps-every-step-you-take-every-move-you-make-googles-got-maps-for-you-20121115-29e1b.html

http://redpin.org/

More Technologies

http://www.directionsmag.com/entry/10-things-you-need-to-know-about-indoor-positioning/324602

iBeacon - http://en.wikipedia.org/wiki/IBeacon, uses bluetooth. Lower range, can be used to calculate position, requires database connectivity, designed to be context aware rather than used for positioning.

Blue-Dot - http://searchengineland.com/aruba-networks-enables-blue-dot-indoor-navigation-beacons-209405, similar to iBeacon.

Seismic Data -http://www.fastcodesign.com/1671857/can-this-design-student-build-an-open-source-alternative-to-gps#8

More technologies listed here - http://en.wikipedia.org/wiki/Indoor_positioning_system

You might be asking, how is SPS different to any of the above?