How to use RTCM data to achieve RTK? - c++

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