Why skyviper can get DGPS 3D lock with it’s original EvaM8M gps chip without receiving RTCM message?

Huibean · April 22, 2018, 10:26am

@amilcarlucas thanks man, ublox m8p would be my rtk choice, but before that I would like to test this, d-gps, not RTK yet

amilcarlucas · April 22, 2018, 10:35pm

RTCM can not be used together with SBAS…
That is bad news.

Please do post if you get RTCM to run.

Huibean · April 23, 2018, 4:23am

@amilcarlucas just disable SBAS and made it work with RTCM2.3,here are some static test

Disable SBAS and get 3D fix, 2D acc 1.10m

WechatIMG22.jpeg2560×1440 382 KB
Enable SBAS and get DGNSS fixed, 2D acc 0.91m

WechatIMG24.jpeg2560×1440 392 KB
Disable SBAS, send RTCM2.3 and get DGNSS fixed, 2D acc 0.84m

WechatIMG23.jpeg2560×1440 367 KB

by the way, these RTCM2.3 message is getting from commercial NTRIP server,I still have trouble converting my M8P base station’s RTCM3.2 output to 2.3

Huibean · April 25, 2018, 3:01am

what is the different between GPS_INJECT_DATA and GPS_RTCM_DATA, I am trying to send rtcm2 to gps through Ardupilot, but both of these two mavlink message not working, here are some data samples

GPS_INJECT_DATA {target_system : 1, target_component : 0, len : 110, data : Y~}qGnPxrO~oLFkABO@|M@`m_I@^nBDAXhC`A_@bCV@@RK@cM_r]X}on}@@@n_vAV@d@@Zf@pvS|YbYF|nGM^|Mp~_dd[{c\@fM`I}
GPS_INJECT_DATA {target_system : 1, target_component : 0, len : 110, data : IAKfORfwAPqw@Z{Ek@lxoEIaA@ejma@P}AcDHV@xI@CIA@@MfUB@UxZiEOFB@Av~JXq}{SVXH@PNP{aAH@AKFm~{wECT@Pl_GNQ}
GPS_INJECT_DATA {target_system : 1, target_component : 0, len : 20, data : @AEDxx{cormoPpe@@J}
GPS_INJECT_DATA {target_system : 1, target_component : 0, len : 110, data : fAB@NxqdGfO~oLc@T~}U@|M@ER`vDnAHAeW|_^R@bCV@@R{wM_rxg~_QX@t@\vAh[eYO@IlC@f]fyC@QxJlCjOA`[~[{cyYr_S}
GPS_INJECT_DATA {target_system : 1, target_component : 0, len : 110, data : IAnY@xm`wAPqw@X{EGSOPCIaA@eZ|m]@o|FcDHV@xE@av~WfUB@pGE\zQFB@AS@Aucq}{SVXH@PNP{aAH@AKFm~{wE]T@Pc_GO~}
GPS_INJECT_DATA {target_system : 1, target_component : 0, len : 20, data : ~z{bx{cJMR@PJpe@@o}

amilcarlucas · April 25, 2018, 3:34pm

GPS_INJECT_DATA is deprecated
Use GPS_RTCM_DATA but make sure you get the flags right. There is one mavproxy module that does this for you.

Huibean · April 25, 2018, 3:55pm

@amilcarlucas so nice see your rely at this moment! I just extract code from that module, and find that gps fixed type did not changed, and in order to check the data, I also write data to telem1 like this

AP_GPS_Backend::inject_data(const uint8_t *data, uint16_t len)
{
    // not all backends have valid ports
    //
    if (port != nullptr) {
        if (port->txspace() > len) {
            port->write(data, len);
            hal.uartC->write(data, len);

then I get that data out from uart tools, the data len is much longer, working overnight to solve this
Is my way wrong?

amilcarlucas · April 25, 2018, 4:15pm

The ardupilot code already copes with RTCM messages upto around 700 bytes. Those are segmented into multiple GPS_RTCM_DATA packets in the ground station, and assembled together by the ardupilot FW, before getting sent to the GPS device.

Longer messages get discarded by mavproxy.

I do not understand your question.

Huibean · April 25, 2018, 5:04pm

@amilcarlucas just write a simple UDP server and tried mavproxy dgps module, it performed the same as my code, when I directly connect to the gps and send RTCM it works

Huibean · April 26, 2018, 3:20am

@amilcarlucas here is the picture of rtcm2.3 input and flight controller output, I guess the message is mess up already

I have check *data’s uint8_t value from AP_GPS_Backend::inject_data(const uint8_t *data, uint16_t len)
it seems correct(the same with MAVLink_gps_rtcm_data_message’s data playload, both value and order), I also use hal.uartC->write(data, len) in the same time, it just not output what I want, maybe I am not familiar with the UART func with ardupilot, when I try hal.uartC->write(‘d’), it just output a two byte value, by the way uartC has been set to a none data output protocol like Beacon

amilcarlucas · April 26, 2018, 7:41am

What is your GPS_INJECT_TO parameter ?

Huibean · April 26, 2018, 7:53am

@amilcarlucas send_to_all

Michael_Oborne · April 26, 2018, 8:09am

the output from the gps port is showing it has not detected any gps. its still scanning for the ublox gps, which i asume is not connected.

change the gps type to force the ublox driver.

as what you are seeing now is the autodetect code output

Huibean · April 26, 2018, 8:29am

@Michael_Oborne My mind is a little wired, cause hal.uartC->write not getting output as I expected, so in order to get origin fc gps port output to find out what is going on, I just pull gps out when gps detect and config is done and plug my uart tool in , but I check the fc debug console, AP_GPS_Backend::inject_data is still executing as I put some log there

In another way, I also tried inject rtcm2.3 in mission planner with tcp connection to data source which shows mp can receive data, but not sending to fc, rtcm3.2 output from M8P in connection with serial works fine, I guess mp not working with rtcm2.3?

Huibean · April 27, 2018, 1:58pm

just find another way to get origin fc gps port output, made sure that the rtcm injection function is good, also send 0x00~0xFF as rtcm data, value and order is both correct, maybe it the ublox config problem? next to find out

Huibean · April 30, 2018, 6:30am

@amilcarlucas @Michael_Oborne Finally solve this! ublox driver auto config code’s setting is UBX +NEMA+RTCM3 so using RTCM2 need to change config，maybe another params option would be better(sending this config by mavlink is also convenient)

github.com

ArduPilot/ardupilot/blob/master/libraries/AP_GPS/AP_GPS_UBLOX.h#L40


*
* First we send a ubx binary message that enables the NAV_SOL message
* at rate 1. Then we send a NMEA message to set the baud rate to our
* desired rate. The reason for doing the NMEA message second is if we
* send it first the second message will be ignored for a baud rate
* change.
* The reason we need the NAV_SOL rate message at all is some uBlox
* modules are configured with all ubx binary messages off, which
* would mean we would never detect it.
*/
#define UBLOX_SET_BINARY "\265\142\006\001\003\000\001\006\001\022\117$PUBX,41,1,0023,0001,115200,0*1C\r\n"


#define UBLOX_RXM_RAW_LOGGING 1
#define UBLOX_MAX_RXM_RAW_SATS 22
#define UBLOX_MAX_RXM_RAWX_SATS 32
#define UBLOX_GNSS_SETTINGS 1


#define UBLOX_MAX_GNSS_CONFIG_BLOCKS 7
#define UBX_MSG_TYPES 2


#define UBLOX_MAX_PORTS 6

amilcarlucas · April 30, 2018, 5:14pm

Good catch. Thanks.
But why are you using RTCM2 ?
RTCM 3.1 is a lot more data rate efficient.

Huibean · May 1, 2018, 6:11am

@amilcarlucas RTCM 3.x is more efficient, but for most lower cost chip, it only accept rtcm2.3, another option for me is running RTK software in Companion Computer, but this would reduce reliability and EVA-M8M seems not support raw data mode to output original measurement data

amilcarlucas · May 1, 2018, 12:07pm

OK, I get it now. Good work figuring all this out !!

grone · January 9, 2022, 3:24pm

@Huibean what are you using to send RTCM messages?

grone · January 11, 2022, 12:11am

I’ve found a problem with ArduPilot’s uBlox configuration.
Initialisation tries to set config by speaking NMEA but the module is only listening to ubx packets.
This is solved by
#define UBLOX_SET_BINARY_115200 "\265\142\006\001\003\000\001\006\001\022\117\265\142\006\000\024\000\001\000\000\000\320\010\000\000\000\302\001\000\007\000\001\000\000\000\000\000\276\162"
which sets CFG PRT to listen to ubx+NMEA+RTCM2 by means of ubx binary packets.
I am now able to fix NTRIP DGPS with SkyViper Journey ( ͡° ͜ʖ ͡°)
This also allows us get rid of the GPS_DRV_OPTIONS=4 hack.