GPS Data : height

[FrankUlbrich]

{ "altitude": -19436, "hdop": 2.2, "latitude": 11.835103144353809, "longitude": 29.48182400952723 }

Hello Björn, I get false altitude in TTN from the network tester. I will try to dig out the problem.

M5StackFire with GPS Shield (Serial Pins changed) I am using this library: TinyGPSPlus-1.0.2

[Bjoerns-TB]

Hi Frank,

at first i would check with the GPS example sketch if you get the correct readings there. Next i would check what the sketch reads:

insert Serial.println(alt); in thegpsdata() function.

Now you will get the altitude on the serial monitor.

[FrankUlbrich]

I added a print output to the sketch:

//Write GPS-Data into variables
void gpsdata() {
  year = gps.date.year();
  month = gps.date.month();
  day = gps.date.day();
  hour = gps.time.hour();
  minute = gps.time.minute();
  second = gps.time.second();
  latitude = gps.location.lat();
  longitude = gps.location.lng();
  alt = gps.altitude.meters();
  hdop = gps.hdop.value();
  Serial.println(F("---------------"));
  Serial.print(F("GPS altitude: "));
  Serial.println(alt);
  Serial.print(F("GPS latitude: "));
  Serial.println(latitude);
  Serial.print(F("GPS longitude: "));
  Serial.println(longitude);
}

#

And I get the following Output , which looks OK. These are my Coordinates. It is nearly the same data which I have on the SD Card in the json / gpx logging. ----- Serial Output:

16:02:58.978 -> --------------- 16:02:58.978 -> GPS altitude: 39.70 16:02:58.978 -> GPS latitude: 51.34 16:02:58.978 -> GPS longitude: 6.34 16:02:59.215 -> --------------- 16:02:59.215 -> GPS altitude: 39.50 16:02:59.215 -> GPS latitude: 51.34 16:02:59.215 -> GPS longitude: 6.34 16:02:59.250 -> --------------- 16:02:59.250 -> GPS altitude: 39.50 16:02:59.250 -> GPS latitude: 51.34 16:02:59.250 -> GPS longitude: 6.34 16:02:59.453 -> --------------- 16:02:59.453 -> GPS altitude: 39.50 16:02:59.453 -> GPS latitude: 51.34 16:02:59.453 -> GPS longitude: 6.34 16:02:59.487 -> --------------- 16:02:59.487 -> GPS altitude: 39.50 16:02:59.487 -> GPS latitude: 51.34 16:02:59.487 -> GPS longitude: 6.34 16:02:59.725 -> --------------- 16:02:59.725 -> GPS altitude: 39.50 16:02:59.725 -> GPS latitude: 51.34 16:02:59.725 -> GPS longitude: 6.34 16:02:59.725 -> --------------- 16:02:59.725 -> GPS altitude: 39.50 16:02:59.725 -> GPS latitude: 51.34 16:02:59.725 -> GPS longitude: 6.34

[FrankUlbrich]

The data send to the TTN does look different.

{
  "altitude": -29681,
  "hdop": 2.7,
  "latitude": 12.538228186263325,
  "longitude": 32.294324177165294
}

Metadata

{
  "time": "2020-06-28T14:02:51.78422952Z",
  "frequency": 867.5,
  "modulation": "LORA",
  "data_rate": "SF7BW125",
  "coding_rate": "4/5",
  "gateways": [
    {
      "gtw_id": "eui-b827ebfffe164cc5",
      "timestamp": 231041092,
      "time": "2020-06-28T14:02:50.755622Z",
      "channel": 5,
      "rssi": -73,
      "snr": 7.8,
      "latitude": 51.34248,
      "longitude": 6.33836,
      "altitude": 39
    }
  ]
}

I guess the Upload Function may not work properly.

[FrankUlbrich]

Hi maybe my problem is, that I have an TTN Mapper decoder in place.

function Decoder(bytes, port) {
    var decoded = {};

    decoded.latitude = ((bytes[0]<<16)>>>0) + ((bytes[1]<<8)>>>0) + bytes[2];
    decoded.latitude = (decoded.latitude / 16777215.0 * 180) - 90;

    decoded.longitude = ((bytes[3]<<16)>>>0) + ((bytes[4]<<8)>>>0) + bytes[5];
    decoded.longitude = (decoded.longitude / 16777215.0 * 360) - 180;

    var altValue = ((bytes[6]<<8)>>>0) + bytes[7];
    var sign = bytes[6] & (1 << 7);
    if(sign)
    {
        decoded.altitude = 0xFFFF0000 | altValue;
    }
    else
    {
        decoded.altitude = altValue;
    }

    decoded.hdop = bytes[8] / 10.0;

    return decoded;
} 

[Bjoerns-TB]

OMG,

i just realized that i didn‘t attach a propper payload decoder.

Sorry for that. Here is the right one, also compatible with the TTN Mapper:

function Decoder(b, port) {

  var lat = (b[0] | b[1]<<8 | b[2]<<16 | (b[2] & 0x80 ? 0xFF<<24 : 0)) / 10000;
  var lon = (b[3] | b[4]<<8 | b[5]<<16 | (b[5] & 0x80 ? 0xFF<<24 : 0)) / 10000;
  var alt = (b[6] | b[7]<<8 | (b[7] & 0x80 ? 0xFF<<16 : 0)) / 100;
  var hdop = b[8] / 10;

  return {

      latitude: lat,
      longitude: lon,
      altitude: alt,
      hdop: hdop

  };
}

[FrankUlbrich]

Hallo Bjoern, einen Gruß nach Köln. Im moment teste ich gerade die Kodierung , welche Du im https://github.com/Bjoerns-TB/ttn-gps-tracker/blob/master/source/tracker.ino genommen hast. Ich denke, ich werde die Änderungen wieder rückgängig machen und bei Deinem Originalcode bleiben. Jetzt weiß ich ja, wie der zugehörigen Decoder aussieht.

Vielen Dank für die schnelle Antwort.

I found some code in your repository https://github.com/Bjoerns-TB/ttn-gps-tracker/blob/master/source/tracker.ino which is compatible to my TTN T-Beam software and the decoder- I added this to the source code. It works well. So I guess I should close this issue, because it was my fault. Your code is fine.

Next I will undo the changes in my modified code and use your decoder, mentioned above to be complient with your code and development. Thanks a lot for your very quick answer.

[FrankUlbrich]

Thanks a lot for your support.