Best practice for reading high precision components from callback

[adam515]

Hello, thank you for creating this great library.

I didn't see in the examples a recommended way to combine low and high resolution lat, lon, alt using callbacks. Could you please clarity?

Do you setup 2 callbacks like so and then manually merge the data?
GNSS.setAutoPVTcallback(&rtk1Callback);
GNSS.setAutoNAVHPPOSECEFcallback(&rtk2Callback);

Thanks again

[PaulZC]

Hi Adam (@adam515 ),

Correct, you will need to set up separate callbacks for the PVT and HPPOS data. If you are just using Lat and Lon, then HPPOSLLH is what you need. HPPOSECEF will give you High Precision X,Y,Z Earth-Centered Earth-Fixed coordinates.

I'll leave this open for now - please let me know if you need more advice / suggestions.

Best wishes,
Paul

[adam515]

Thank you. That helps a lot.

I am probably doing something wrong because when I turn on high precision with the code below, I get more decimal points but the reported accuracy is much lower (140mm vs. 11mm). Could you please advise?

void initRTKsWithCallback() {
// GNSS1.enableDebugging(); // Uncomment this line to enable helpful debug messages on Serial

if (GNSS1.begin(Wire1) == false) { //Connect to the u-blox module using Wire port
Serial.println(F("u-blox GNSS1 not detected at default I2C address. Please check wiring."));
delay(200);
}
GNSS1.setI2COutput(COM_TYPE_UBX); //Set the I2C port to output UBX only (turn off NMEA noise)
GNSS1.setAutoPVT(true); //Tell the GNSS to "send" each solution
//GNSS1.saveConfigSelective(VAL_CFG_SUBSEC_IOPORT); //Save (only) the communications port settings to flash and BBR
GNSS1.setNavigationFrequency(20); //Produce two solutions per second
-------> using this line gives better reported accuracy
//GNSS1.setAutoPVTcallback(&rtk1Callback); // Enable automatic NAV PVT messages with callback to rtkCallback
-------> using this line gives worse reported accuracy , counterintuitively
GNSS2.setAutoHPPOSLLHcallback(&rtk1HighPrecisioncallback);
}

Two callback types tested, called from above code:
#1
void rtk1Callback(UBX_NAV_PVT_data_t d) {
rtk1_lat = double(d.lat)/1e-7;
rtk1_lon = double(d.lon)/1e-7;
rtk1_alt = float(d.height)/1000;
rtk1_accuracy = d.hAcc;
rtk1_heading = d.headVeh;
rtk1_num_satellites = d.numSV;
}

#2
void rtk1HighPrecisioncallback(UBX_NAV_HPPOSLLH_data_t d) {
int32_t latitude = d.lat;
int8_t latitudeHp = d.latHp;
int32_t longitude = d.lon;
int8_t longitudeHp = d.lonHp;
int32_t ellipsoid = d.height;
int8_t ellipsoidHp = d.heightHp;
uint32_t accuracy = d.hAcc;

// Assemble the high precision latitude and longitude
double d_lat = ((double)latitude) / 10000000.0; // Convert latitude from degrees * 10^-7 to degrees
d_lat += ((double)latitudeHp) / 1000000000.0; // Now add the high resolution component (degrees * 10^-9 )
double d_lon = ((double)longitude) / 10000000.0; // Convert longitude from degrees * 10^-7 to degrees
d_lon += ((double)longitudeHp) / 1000000000.0; // Now add the high resolution component (degrees * 10^-9 )

float f_ellipsoid;
// Calculate the height above ellipsoid in mm * 10^-1
f_ellipsoid = (ellipsoid * 10) + ellipsoidHp;
// Now convert to m
f_ellipsoid = f_ellipsoid / 10000.0; // Convert from mm * 10^-1 to m

rtk1_lat = d_lat;
rtk1_lon = d_lon;
rtk1_alt = f_ellipsoid;
rtk1_accuracy = accuracy;
rtk1_num_satellites = d.vAcc;
}

in loop():
calling
void ReadGNSSCallback() {
if (millis() - last_rtk_read > 50) {
last_rtk_read = millis();
GNSS1.checkUblox(); // Check for the arrival of new data and process it.
GNSS1.checkCallbacks(); // Check if any callbacks are waiting to be processed.
}
}

[PaulZC]

Hi Adam (@adam515 ),

I guess you are using the ZED-F9P?

It's the scaling that is tripping you up. In the PVT message, the units for hAcc are mm (no scaling). For HPPOSLLH, the units are mm but the scaling is 0.1. Your 140mm is actually 14.0mm:

SparkFun_u-blox_GNSS_Arduino_Library/src/u-blox_structs.h

Line 713 in 63194e7

uint32_t hAcc; // Horizontal accuracy estimate: mm * 0.1

I'm happy to leave this issue open if you need a bit more help - it is a useful tutorial for other users. But please close once you think we're all done.

Best wishes,
Paul

[adam515]

Thank you that was indeed the issue. I will close this thread and thank you for your advice.