TdhZones reports location relative to defined polygons (geofencing) using coordinates obtained from the device on which the app is running. Polygons used by TdhZones are defined within an sqlite database that may be created, viewed and edited using the TdhGIS personal computer software. Coordinates used by the polygons may be longitude/latitude or any coordinates that can be obtained by converting from long/lat data using the Proj4 library.

A typical use of TdhZones would be determining the name of the state where the device is located or is nearest to. The sample data included defines the states for the USA based on data provided at census.gov. TdhGIS includes the ability to import shapefiles, which is how the sample data was created.

TdhZones comes in 2 versions, a local version and a client/server version.

The local version, TdhZones, stores the geo database and performs the spatial analysis on the mobile device. For this version, no network connection is needed and no further information, other than device coordinates, is needed for the app to function. It does not request Communication permission so it does not and can not transmit location information.

The client version, TdhZonesC relies on the free server program to access the geo database and perform the spatial analysis. For this version, a single database may be accessed by many users and a network connection is required. The client version requires Communication permission. The server program may run on Linux or MS Windows.

Both versions of TdhZones run on Android 4.1 or higher and require permissions for Fine Location. Coordinates are obtained only on user command (i.e. no constant polling to run down device battery). Neither version stores location information nor uses location information for any purpose other than as described within this document.

About the author; Tim Hirrel (timhirrel@tdhnet.com)