VRS With RTCM 3.1 Transformation Messages

Joy Chiu

New Member
Our NLSC(National Land Surveying and Mapping Center) offer VRS (Virtual Reference Stations) service, that use RTCM 3.1 Transformation Messages In RTK GNSS Networks
They use Trimble TTG (Trimble Transformation Generator)
- RTCM3.1 include "1021(Helmert / Abridged Molodenski Transformation)" and "1023(Transformation Residual Message, ellipsoidal grid representation)"

* How to setting this on J-Field of TRIUMPH-LS?
 

Matt Johnson

Well-Known Member
5PLS
I don't believe that transformation messages are currently supported in J-Field. If this is something that is needed, support could probably be added for transformation messages. Do you have anymore information or a link to documentation about the network you are trying to connect to?
 

Vladimir Prasolov

Well-Known Member
JAVAD GNSS
Gentlemen,

Transformation messages are not supported in J-Field for now. Receiver itself is parsing and using RTCM3.x transformation messages and converting it to JASON-similar text message. They could contain Helmert Datum transformation parameters, some projections, and horizontal and vertical shifts. I did some work to convert RTCM3.x transformations to our XML format. The main issue is related to parameters (especially small 4x4 grids) could vary from one place to another during survey session. We have plan to finish that task.
The parameters could be requested from receiver by NetView. Or they could be parsed from RTCM messages that wrapped in raw data on Triumph-LS. Or they could be requested from VRS provider. We have rich enough transformation library to define transformation on J-Field side. I did that for Doug, and it worked.
Could you please request NLSC regarding what coordinate system is required and what frame they are using during corrections broadcasting WGS84 or NAD83 at some particular epoch.
 

Joy Chiu

New Member
Could you please request NLSC regarding what coordinate system is required and what frame they are using during corrections broadcasting WGS84 or NAD83 at some particular epoch.
Check on here→ http://210.241.63.193:81/

STR;TTG_2010;TTG_2010;RTCM 3.1;;2;GPS+GLONASS;NLSC;TWN;22.8;120.4;1;1;Trimble Pivot Platform;none;B;Y;12600;;
STR;TTG_TWD97;TTG_TWD97;RTCM 3.1;;2;GPS+GLONASS;NLSC;TWN;22.8;120.4;1;1;Trimble Pivot Platform;none;B;Y;12600;;
 

Vladimir Prasolov

Well-Known Member
JAVAD GNSS
Could you please request NLSC regarding what coordinate system is required and what frame they are using during corrections broadcasting WGS84 or NAD83 at some particular epoch.
Check on here→ http://210.241.63.193:81/

STR;TTG_2010;TTG_2010;RTCM 3.1;;2;GPS+GLONASS;NLSC;TWN;22.8;120.4;1;1;Trimble Pivot Platform;none;B;Y;12600;;
STR;TTG_TWD97;TTG_TWD97;RTCM 3.1;;2;GPS+GLONASS;NLSC;TWN;22.8;120.4;1;1;Trimble Pivot Platform;none;B;Y;12600;;
Please contact with RTN customer service and ask them to give coordinate system (reference frame) name and epoch of broadcasted RTCM 3.x corrections. For example when we asked Can-Net RTN. They provided the following list in documentation:

Nova Scotia – NAD 83 CSRS epoch 1997.0 (v3.0.0)
PEI – NAD 83 CSRS epoch 1997.0 (v2.0.0)
New Brunswick – NAD 83 CSRS epoch 1997.0 (v2.0.0)
Quebec – NAD 83 CSRS epoch 1997.0 (v2.0.0)
...

Also could you please ask what grid and vertical system are required for that county.
Could you provide approximate position of working area. We will try to send GGA and receive transformation.
 

Vladimir Prasolov

Well-Known Member
JAVAD GNSS
Hi Joy,
Please create some project on Triumph-LS. Then connect to NLSC and collect one point with saving raw data. Export the project and send zip file to this forum ("Upload a File"). We will extract RTCM messages from that file.
 

Vladimir Prasolov

Well-Known Member
JAVAD GNSS
Dear Lydia,

Thank you for providing access to NLSC mount points. We did verify coordinate transformations from RTCM 3.1 streams.

1. We found some incompatibility with RTCM 3.1 standard in the stream. So current version of receiver firmware doesn't work for that stream. Our firmware team relaxed requirements for transformation messages. It worked fine. That version 3.6.3 will be released soon.
2. The transformed position could be received in $GPGGA NMEA message from receiver.
3. Currently we have task to use those transformed coordinates in J-Filed. The developer of that task will be on vacation two more week. After that we will try to implement that as soon as possible.
4. For now you can select horizontal grid TWD97 / Penghu with EGM2008 geoid for vertical system (you can unzip attached file and import it). The horizontal difference is in centimeter range, but the vertical has some decimeters compare with RTCM transformations. For better accuracy you can stay on one (or more) of known (reference) point and use Localization.
5. In any case, could you please to survey some reference point, to see what accuracy the included implementation has. I loaded 592 control points on Triumph-LS and found it is very accurate - the RMSE is 2mm and maximum error is about 2.4mm.
 

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