Parsing NMEA sentences from serial - c++

Question

I want to use TinyGPS++ on an Arduino to parse NMEA data and display information on an OLED display. But, instead of using software serial and the TX/RX pins, the NMEA data will be received by USB.
I followed the examples from TinyGPS++, but i encountered two problems:
1)
Only the first 64 characters are received by the Arduino, when i send one NMEA sentence over the serial monitor (Windows, Arduino 1.6.9). How can I overcome this restriction? I help myself by deleting a couple of decimal places, but this is not the preferred way to go.
2)
In the TinyGPS++ BasicExample a sample NMEA string is defined in the read-only memory:
// A sample NMEA stream.
const char *gpsStream =
"$GPRMC,045103.0,A,3014.0,N,09748.0,W,36.88,65.02,030913,,,A*7C\r\n"
"$GPGGA,045104.0,3014.0,N,09749.0,W,1,09,1.2,211.6,M,-22.5,M,,*62\r\n"
"$GPRMC,045200.0,A,3014.0,N,09748.0,W,36.88,65.02,030913,,,A*77\r\n"
"$GPGGA,045201.0,3014.0,N,09749.0,W,1,09,1.2,211.6,M,-22.5,M,,*6C\r\n"
"$GPRMC,045251.0,A,3014.0,N,09748.0,W,36.88,65.02,030913,,,A*7D\r\n"
"$GPGGA,045252.0,3014.0,N,09749.0,W,1,09,1.2,211.6,M,-22.5,M,,*6F\r\n";
and parsed by
while (*gpsStream) {
Serial.print(*gpsStream);
gps.encode(*gpsStream++);
}
I receive my NMEA (unfortunately only one line) this way:
if (Serial.available()) {
while (Serial.available() > 0) {
if(index < 80)
{
inChar = Serial.read();
inData[index] = inChar;
index++;
inData[index] = '\0';
}
}
}
and try to parse it by:
index = 0;
while (index < 80) {
gps.encode(inData[index]);
Serial.print(inData[index]);
index++;
}
But this does not work as desired. Checking if the location isValid() always returns not to be true.
Unfortunately, i have several possible sources for this undesired behavior.
The too short sentences (unlikely)
Incorrect way of reading the data over serial.
I only submit one line.
Something else.
I am not that experienced with neither NMEA, nor the serial data communication, and i have only little experience with Arduino/C. Can you point me into a direction how to solve for this (these) problems?

Answer 1

Basically, you do not need to accumulate NMEA characters. Just feed them to the GPS library as you receive them. You don't provide the entire loop, but it is very common to have a problem there, too.
After struggling with several GPS libraries and their examples, I eventually wrote NeoGPS. It is faster and smaller than all other libraries, it validates the checksum, and the examples are structured correctly. Unlike other libraries, NeoGPS does not store GPS values as floating-point values, so it is able to retain the full accuracy of your GPS device.
If you'd like to try it, be sure to follow the Installation instructions. The NMEA.ino example will emit one line of info (CSV format) for each batch of GPS sentences that you send, ending with the default RMC sentence. Be sure to modify it to use the Serial object instead of gps_port, or simply define it that way:
#define gps_port Serial
It will also show the number of characters that have been parsed, how many good sentences have been received, and how many sentences had checksum errors. That could help with debugging if you are not generating the checksum correctly. This site is useful, too.
Those CSV lines will be sent back over the USB port (to the PC), but you can easily change it to send specific fields to the OLED (see NMEAloc.ino).
Although it is possible to develop something on a PC and then port it to an embedded environment like the Arduino, you have to be careful about (1) linear program structure and (2) ignoring resource limits (program size, MCU speed and RAM). There are a number of quirks with the Arduino environment that usually make it frustrating to port a "sketch" to/from a PC. :P