原创 NV08C系列产品开发问答（二）

8.有没有实际高精度测试数据可参考？
我们进行了很多高精度测试，如NV08C-RTK、NV08C-RTK-A，后者包含定向、航向。
如下是来自某航空摄影客户测试NV08C-RTK的数据：

图中纵坐标1小格是1mm误差，纬度、经度误差-1～+1mm，高程误差-3～+2mm（极大部分点落在此区域）
高程误差分布图

图中横坐标1小格是1mm误差，纬度、经度误差-1～+1mm，高程误差-3～+2mm（极大部分点落在此区域）

9. DGNSS与RTK

虽然同样依赖2台接收机工作，DGNSS差分与RTK实时动态差分（又称载波相位差分）还是不同。

DGNSS系统，举例一台高性能接收机（基站），一台NV08C-CSM接收机（流动站），NV08C-CSM接收到基站发出的RTCMv2.x电文messages #1和#31。

RTCMv2.x并不使用基站坐标。

message #1为所有可视GPS卫星改正电文。

message #31为所有可视Glonass卫星改正电文。

DGNSS system, RTCMv2.x messages #1 and #31

RTCMv2.x does not need to use base coordinates

message #1 is corrections for all visible GPS SVs

message #31 is corrections for all visible GLONASS SVs

RTK系统，流动站接收基站发出的RTCMv3.x电文，RTCMv3.x电文包含原始数据，流动端需要基站坐标计算、改正原始数据。

GPS & GLONASS改正信息(RTCMv2.x) ，或者是GPS & GLONASS原始数据+ 基站坐标(RTCMv3.x) 都能提高精度。

基站坐标输入两条命令即可$PNVGRTL,BACexYZ或$PNVGRTL,BASEBLH。

原始数据或当前可视卫星的改正信息是DGNSS或RTK观测的主要部分，基站坐标数据对RTK是必要的但并不足够，主要改正源仍然是观测基站可视卫星的原始数据。

Base transmits RTCM messages 1002, 1006, 1010

1006 is message with Base coordinates

1002 - raw data for GPS

1010 - raw data for GLONASS

all these messages are necessary for RTK

1006 message only is not enough.

RTCMv3.x contains raw data and therefore needs base coordinates to calculate raw data corrections on Rover side,

but raw data or corrections for currently visible SVs is the main part of DGNSS or RTK method, base coordinates are just necessary information but not all, the main correction source here is raw data from visible SVs which are measured at Base Station side.

附：RTCM现有不同版本(括号内容表示变化)
RTCM 2.0 :仅用于DGPS （Code Correction-->DGPS）

RTCM 2.1 : 添加载波相位数据和RTK修正数据 (Code+Phase Correction-->RTK )

RTCM 2.2 : 包括了GLONASS 数据和相关信息 (...+Glonass)

RTCM 2.3 : 增加antenna types (message 23) ARP information (message 24) (...+GPS Antenna Definition)

RTCM 3.0 : RTCM 2.3 requires 4800 bps to broadcast dual-frequency code and carrier-phase observation corrections of 12 satellites. The information content is send with 1800 bps in RTCM 3.0 。增加了新的GNSS系统 (...+ Network RTK & GNSS)

GPS RTK Observations

1001 GPS L1 observations
1002 GPS L1 observations, extended information 1)
1003 GPS L1+L2 observations
1004 GPS L1+L2 observations, extended information 1)
1) Extended information contains Signal-to-Noise (CNO) and full milliseconds for code observations.

Stationary Antenna Reference Point

1005 ARP station coordinates, ECEF XYZ
1006 ARP station coordinates, ECEF XYZ and extended information 2)
2) Extended information contains the antenna height.

Antenna Description

1007 antenna type
1008 antenna type, extended information 3)
3) Extended information contains the antenna serial number.

GLONASS Observations

1009 GLONASS L1 observations
1010 GLONASS L1 observations, extended information 4)
1011 GLONASS L1+L2 observations
1012 GLONASS L1+L2 observations, extended information 4)
4) Extended information contains Signal-to-Noise (CNO) and full milliseconds for code observations.

System Parameters

1013 system parameters, list of transmitted message types and update rates

RTCM 3.1

Network Message

1014 Network Auxiliary Station Data
coordinate difference between one Aux station and the master station
1015 GPS Ionospheric Correction Differences for all satellites between one Aux station and the master station
1016 GPS Geometric Correction Differences for all satellites between one Aux station and the master station
1017 GPS Combined Geometric and Ionospheric Correction Differences for all satellites between one Aux station and the master station
(same content as both types 1015 and 1016 together, but less size)
1018 RESERVED for Alternative Ionospheric Correction Difference Message.Message type 1018 is not yet defined.

Ephemeris Data

1019 GPS Ephemeris
1020 GLONASS Ephemeris

UTF8 Text Message

1029 Text in UTF8 format (max. 127 multibyte characters and max. 255 bytes)

RTCM 3.1 Addendum 1

Transformation Message

1021 Helmert / Abridged Molodenski Transformation
1022 Molodenski-Badekas Transformation
1023 Transformation Residual Message, ellipsoidal grid representation
1024 Transformation Residual Message, plane grid representation
1025 Projection types except LCC2SP, OM
1026 Projection type Lambert Conic Conformal (LCC2SP)
1027 Projection type Oblique Mercator (OM)
1028 RESERVED for Global to Plate Fixed Transformation(Message type 1028 is not yet defined.)

RTCM 3.1 Addendum 2

Network Residuals Messages

1030 GPS Network Residuals
1031 GLONASS Network Residuals

ARP Message for VRS

1032 ARP station coordinates, ECEF XYZ of real reference station

Receiver and Antenna Descriptor

1033 Receiver and Antenna Descriptor

RTCM 3.1 Further Addendums

Further message types proposed for the next future are FKP for GPS and GLONASS, and MAC for GLONASS.

Network FKP Messages

1034 GPS FKP
1035 GLONASS FKP



10.NV08C-RTK的不能

囿于内部结构及运算机制局限，NV08C-RTK不适合要求延时非常小（如小于10毫秒）的场合，NovAtel CPT也不能！此时，需要用到其它惯性导航模块，如Spatial延时（Latency）仅仅0.4毫秒。

11.北斗差分

我国多项北斗国际标准提案，已被国际海事无线电技术委员会RTCM第104专业委员会（RTCM SC-104）接受。随着北斗进入RTCM、NMEA、IGS、NGS等国际系列标准，北斗的作用、威力将大大增强。但目前相比Glonass进入RTCM3.1标准，北斗做得远远不够。

NV08C-CSM默认串口2为BINR，需要设置为RTCM，支持RTCM v2.x messages #1与 #31.
Message #1 是GPS corrections, message #31是GLONASS corrections。由于北斗差分相关信息没有公开，目前固件（Firmware）不支持北斗RTCM，待将来升级FW可以完全支持GPS、北斗差分RTCM，目前版本只支持GPS差分RTCM v2.x messages #1、Glonass差分RTCM message #31。