# Choosing your configuration There are only a few configurations provided by examples. If your application needs something slightly different, here is a general configuration process. ## What number do you want? First, decide which data members of `gps_fix` and `NMEAGPS` you need (see [Data Model](Data Model.md) for member descriptions). Those members **must** be enabled in `GPSfix_cfg.h`. Next, figure out what messages can fill out those members, because those messages **must** be enabled in `NMEAGPS_cfg.h`. Here is a table of the NMEA messages parsed by NeoGPS, and which data members they affect:

Message Data Member	GGA	GLL	GSA	GST	GSV	RMC	VTG	ZDA	PUBX 00¹	PUBX 04¹
class gps_fix
status	*	*	*			*	*		*
date²						*		*		*
time²	*	*		*		*		*	*	*
lat/lon	*	*				*			*
altitude	*								*
speed						*	*		*
heading						*	*		*
satellites ³	*		*						*
HDOP	*		*						*
VDOP			*						*
PDOP			*
TDOP									*
Velocity North, East, Down									* ⁴ * ⁴ *
lat, lon, alt error				*					*
speed error, heading error, time error ⁵
class NMEAGPS
satellite IDs ³			*		*
satellite azimuth, elevation and signal strength ³					*

This table illustrates the poor design of the NMEA message set: it requires multiple messages to deliver a complete fix (i.e., all members of `gps_fix`). This also explains why many manufacturers provide proprietary messages that *are* more complete. Above, you can see that the `$PUBX,00`¹ message contains all members except `date`. While the manufacturer's specification will document all sentences supported for your device, you can also find general descriptions of many NMEA sentences [here](http://www.gpsinformation.org/dale/nmea.htm), [here](http://aprs.gids.nl/nmea/) or [here](http://www.catb.org/gpsd/NMEA.txt).

_{¹ The NMEA proprietary messages "PUBX" are only availble in the `ubloxNMEA` class. See [ublox-specific instructions](ublox.md) for adding this class to your configuration.} _{² Date and time are both stored in one member of `gps_fix`, called `dateTime`. The `fix.dateTime` member is a C++ class that has both date-oriented members (Date, Month and Year) and time-oriented members (Hours, Minutes and Seconds). See [NeoTime.h](/src/NeoTime.h) for the complete description and capabilities of the `dateTime` member, such as date/time arithmetic and conversion to/from seconds since the epoch. Hundredths of a second are stored in a separate member of `gps_fix`, called `dateTime_cs`, and can also be accessed with the functions `dateTime_ms()` and `dateTime_us()`.} _{³ The `fix.satellites` member identifies how many of these satellites were used to calculate a fix. The number of satellites' information available in the `gps.satellites[]` array is stored in `gps.sat_count`. This the total number of satellites that may or may not be used for calculating a fix.

_{⁴ Only Velocity Down is provided by the PUBX,00 message. A utility routine is provided to *calculate* Velocity North and East from Speed and Heading, if enabled. See `calculateNorthAndEastVelocityFromSpeedAndHeading` in gps_fix.h.

_{⁵ These fields are only available from UBX binary messages.}}}