ThingMagic Mercury xPRESS, Platform Manual, Page: 67 / 146

GPS Module
A D I V I S I O N O F T R I M B L E
Using the Optional Modules
67
Configuration
To enable GPS operation, define confINCLUDE_GPS in conf_xpress_reader.h and
make sure GPS_DEVNAME is set to the appropriate USART (“/USART1” for Slot 0 or “/
USART2” for Slot 1.) and also make sure this USART for GPS is not assigned to any
other module in the system. (By default, the GPS module is configured to operate in Slot
1.) The GPS data is parsed in
GPS_process and GPS metadata (latitude and longitude)
is automatically included in tag data of the xPRESS system.
If the “TP” LED on the GPS Bee module is not flashing, then the module has not acquired
the GPS signal and you will see “lat=N/A lon=N/A” added to the metadata of any tag read.
If the “TP” LED on the GPS module is flashing, the GPS location will be included, such as
“lat=42.286064 lon=-71.071184”.
Note
Once the GPS module has been enabled, the GPS location or “N/A” is
always included in the tag string.
GPS Metadata
The prefix and suffix for the GPS metadata is controlled in
conf_xpress_reader.h
.
TAG_LAT_PREFIX, TAG_LAT_POSTFIX
,
TAG_LON_PREFIX
and
TAG_LATLON_POSTFIX
may be defined if desired.
For example, TAG_LAT_PREFIX can be “
lat=
”
The format of the GPS latitude/longitude data itself is numeric decimal degrees, with
negative sign to indicate southerly latitudes or westerly longitudes. (This format is
compatible with Google Maps queries, as described by
https://support.google.com/maps/
answer/18539
). This is not the same as the native NMEA format, which has decimal
degrees, but uses N/S/E/W designators instead of a positive or negative sign.
For example, given the NMEA input value of “42.4731565,N,71.0982345,W” we would
output
lat=42.4731565 lon=-71.0982345
and if NMEA values are not available, we would output as
lat=N/A lon=N/A