How to use RTCM data to achieve RTK?

Question

I'm using this example from the Sparkfun Arduino Library

/*
  Use ESP32 WiFi to get RTCM data from RTK2Go (caster) as a Client
  By: SparkFun Electronics / Nathan Seidle
  Date: November 18th, 2021
  License: MIT. See license file for more information but you can
  basically do whatever you want with this code.
  This example shows how to obtain RTCM data from a NTRIP Caster over WiFi
  and push it over I2C to a ZED-F9x.
  It's confusing, but the Arduino is acting as a 'client' to a 'caster'. In this case we will
  use RTK2Go.com as our caster because it is free. See the NTRIPServer example to see how
  to push RTCM data to the caster.
  You will need to have a valid mountpoint available. To see available mountpoints go here: http://rtk2go.com:2101/
  This is a proof of concept to show how to connect to a caster via HTTP. Using WiFi for a rover
  is generally a bad idea because of limited WiFi range in the field.
  For more information about NTRIP Clients and the differences between Rev1 and Rev2 of the protocol
  please see: https://www.use-snip.com/kb/knowledge-base/ntrip-rev1-versus-rev2-formats/
  Feel like supporting open source hardware?
  Buy a board from SparkFun!
  ZED-F9P RTK2: https://www.sparkfun.com/products/16481
  RTK Surveyor: https://www.sparkfun.com/products/18443
  RTK Express: https://www.sparkfun.com/products/18442
  Hardware Connections:
  Plug a Qwiic cable into the GNSS and a ESP32 Thing Plus
  If you don't have a platform with a Qwiic connection use the SparkFun Qwiic Breadboard Jumper (https://www.sparkfun.com/products/14425)
  Open the serial monitor at 115200 baud to see the output
*/
#include <WiFi.h>
#include "secrets.h"

#include <SparkFun_u-blox_GNSS_Arduino_Library.h> //http://librarymanager/All#SparkFun_u-blox_GNSS
SFE_UBLOX_GNSS myGNSS;

//The ESP32 core has a built in base64 library but not every platform does
//We'll use an external lib if necessary.
#if defined(ARDUINO_ARCH_ESP32)
#include "base64.h" //Built-in ESP32 library
#else
#include <Base64.h> //nfriendly library from https://github.com/adamvr/arduino-base64, will work with any platform
#endif

//Global variables
//=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
long lastReceivedRTCM_ms = 0; //5 RTCM messages take approximately ~300ms to arrive at 115200bps
int maxTimeBeforeHangup_ms = 10000; //If we fail to get a complete RTCM frame after 10s, then disconnect from caster
//=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

void setup()
{
  Serial.begin(115200);
  Serial.println(F("NTRIP testing"));

  Wire.begin(); //Start I2C

  if (myGNSS.begin() == false) //Connect to the Ublox module using Wire port
  {
    Serial.println(F("u-blox GPS not detected at default I2C address. Please check wiring. Freezing."));
    while (1);
  }
  Serial.println(F("u-blox module connected"));

  myGNSS.setI2COutput(COM_TYPE_UBX); //Turn off NMEA noise
  myGNSS.setPortInput(COM_PORT_I2C, COM_TYPE_UBX | COM_TYPE_NMEA | COM_TYPE_RTCM3); //Be sure RTCM3 input is enabled. UBX + RTCM3 is not a valid state.

  myGNSS.setNavigationFrequency(1); //Set output in Hz.

  Serial.print(F("Connecting to local WiFi"));
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(F("."));
  }
  Serial.println();

  Serial.print(F("WiFi connected with IP: "));
  Serial.println(WiFi.localIP());

  while (Serial.available()) Serial.read();
}

void loop()
{
  if (Serial.available())
  {
    beginClient();
    while (Serial.available()) Serial.read(); //Empty buffer of any newline chars
  }

  Serial.println(F("Press any key to start NTRIP Client."));

  delay(1000);
}

//Connect to NTRIP Caster, receive RTCM, and push to ZED module over I2C
void beginClient()
{
  WiFiClient ntripClient;
  long rtcmCount = 0;

  Serial.println(F("Subscribing to Caster. Press key to stop"));
  delay(10); //Wait for any serial to arrive
  while (Serial.available()) Serial.read(); //Flush

  while (Serial.available() == 0)
  {
    //Connect if we are not already. Limit to 5s between attempts.
    if (ntripClient.connected() == false)
    {
      Serial.print(F("Opening socket to "));
      Serial.println(casterHost);

      if (ntripClient.connect(casterHost, casterPort) == false) //Attempt connection
      {
        Serial.println(F("Connection to caster failed"));
        return;
      }
      else
      {
        Serial.print(F("Connected to "));
        Serial.print(casterHost);
        Serial.print(F(": "));
        Serial.println(casterPort);

        Serial.print(F("Requesting NTRIP Data from mount point "));
        Serial.println(mountPoint);

        const int SERVER_BUFFER_SIZE  = 512;
        char serverRequest[SERVER_BUFFER_SIZE];

        snprintf(serverRequest, SERVER_BUFFER_SIZE, "GET /%s HTTP/1.0\r\nUser-Agent: NTRIP SparkFun u-blox Client v1.0\r\n",
                 mountPoint);

        char credentials[512];
        if (strlen(casterUser) == 0)
        {
          strncpy(credentials, "Accept: */*\r\nConnection: close\r\n", sizeof(credentials));
        }
        else
        {
          //Pass base64 encoded user:pw
          char userCredentials[sizeof(casterUser) + sizeof(casterUserPW) + 1]; //The ':' takes up a spot
          snprintf(userCredentials, sizeof(userCredentials), "%s:%s", casterUser, casterUserPW);

          Serial.print(F("Sending credentials: "));
          Serial.println(userCredentials);

#if defined(ARDUINO_ARCH_ESP32)
          //Encode with ESP32 built-in library
          base64 b;
          String strEncodedCredentials = b.encode(userCredentials);
          char encodedCredentials[strEncodedCredentials.length() + 1];
          strEncodedCredentials.toCharArray(encodedCredentials, sizeof(encodedCredentials)); //Convert String to char array
          snprintf(credentials, sizeof(credentials), "Authorization: Basic %s\r\n", encodedCredentials);
#else
          //Encode with nfriendly library
          int encodedLen = base64_enc_len(strlen(userCredentials));
          char encodedCredentials[encodedLen]; //Create array large enough to house encoded data
          base64_encode(encodedCredentials, userCredentials, strlen(userCredentials)); //Note: Input array is consumed
#endif
        }
        strncat(serverRequest, credentials, SERVER_BUFFER_SIZE);
        strncat(serverRequest, "\r\n", SERVER_BUFFER_SIZE);

        Serial.print(F("serverRequest size: "));
        Serial.print(strlen(serverRequest));
        Serial.print(F(" of "));
        Serial.print(sizeof(serverRequest));
        Serial.println(F(" bytes available"));

        Serial.println(F("Sending server request:"));
        Serial.println(serverRequest);
        ntripClient.write(serverRequest, strlen(serverRequest));

        //Wait for response
        unsigned long timeout = millis();
        while (ntripClient.available() == 0)
        {
          if (millis() - timeout > 5000)
          {
            Serial.println(F("Caster timed out!"));
            ntripClient.stop();
            return;
          }
          delay(10);
        }

        //Check reply
        bool connectionSuccess = false;
        char response[512];
        int responseSpot = 0;
        while (ntripClient.available())
        {
          if (responseSpot == sizeof(response) - 1) break;

          response[responseSpot++] = ntripClient.read();
          if (strstr(response, "200") > 0) //Look for 'ICY 200 OK'
            connectionSuccess = true;
          if (strstr(response, "401") > 0) //Look for '401 Unauthorized'
          {
            Serial.println(F("Hey - your credentials look bad! Check you caster username and password."));
            connectionSuccess = false;
          }
        }
        response[responseSpot] = '\0';

        Serial.print(F("Caster responded with: "));
        Serial.println(response);

        if (connectionSuccess == false)
        {
          Serial.print(F("Failed to connect to "));
          Serial.print(casterHost);
          Serial.print(F(": "));
          Serial.println(response);
          return;
        }
        else
        {
          Serial.print(F("Connected to "));
          Serial.println(casterHost);
          lastReceivedRTCM_ms = millis(); //Reset timeout
        }
      } //End attempt to connect
    } //End connected == false

    if (ntripClient.connected() == true)
    {
      uint8_t rtcmData[512 * 4]; //Most incoming data is around 500 bytes but may be larger
      rtcmCount = 0;

      //Print any available RTCM data
      while (ntripClient.available())
      {
        //Serial.write(ntripClient.read()); //Pipe to serial port is fine but beware, it's a lot of binary data
        rtcmData[rtcmCount++] = ntripClient.read();
        if (rtcmCount == sizeof(rtcmData)) break;
      }

      if (rtcmCount > 0)
      {
        lastReceivedRTCM_ms = millis();

        //Push RTCM to GNSS module over I2C
        myGNSS.pushRawData(rtcmData, rtcmCount, false);
        Serial.print(F("RTCM pushed to ZED: "));
        Serial.println(rtcmCount);
      }
    }

    //Close socket if we don't have new data for 10s
    if (millis() - lastReceivedRTCM_ms > maxTimeBeforeHangup_ms)
    {
      Serial.println(F("RTCM timeout. Disconnecting..."));
      if (ntripClient.connected() == true)
        ntripClient.stop();
      return;
    }

    delay(10);
  }

  Serial.println(F("User pressed a key"));
  Serial.println(F("Disconnecting..."));
  ntripClient.stop();
}

on an ESP32 Thing Plus C with a ZED-F9P and it's working fine, but it only outputs RTCM data. How do I apply the RTCM data to the GPS data and achieve RTK? My goal is to have the ESP32 Thing Plus C output RTK Latitude and Longitude to the serial monitor.

Example output:

RTCM pushed to ZED: 163

RTCM pushed to ZED: 311

RTCM pushed to ZED: 1694

RTCM pushed to ZED: 1332

Any ideas would be appeciated! Thanks

Answer 1

Answered by PaulZC on Sparkfun Forum

Hi Jacob,

It sounds like everything is working OK. But, correct, there is nothing in that example to actually print out the position.

Please try Example17. It is better-structured and uses callbacks to: display your position; and push NMEA GGA data to the server. Some NTRIP servers require the GGA data, others don't. If the GGA data causes problems, you can comment this line to disable the push:

https://github.com/sparkfun/SparkFun_u- ... ck.ino#L81

Have fun! Paul