Difference between revisions of "NMEA Format"

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(Created page with "The OEM 719 outputs the data collected after the receiver does it's calculations in the NMEA2000 format by default. NMEA2000 messages are sent as packets that consis...")
 
 
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The [[GPS | OEM 719]] outputs the data collected after the receiver does it's calculations in the NMEA2000 format by default. NMEA2000 messages are sent as packets that consist of a header followed by (typically) 8 bytes of data. The header for a message specifies the transmitting device, the device to which the message was sent (which may be all devices), the message priority, and the PGN (Parameter Group Number). The PGN indicates which message is being sent, and thus how the data bytes should be interpreted to determine the values of the data fields that the message contains.
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The [[GPS | OEM 719]] outputs the data collected after the receiver does it's calculations in the NMEA2000 format by default. NMEA2000 messages are sent as packets that consist of a header followed by (typically) 8 bytes of data. The header for a message specifies the transmitting device, the device to which the message was sent (which may be all devices), the message priority, and the PGN (Parameter Group Number). The PGN indicates which message is being sent, and thus how the data bytes should be interpreted to determine the values of the data fields that the message contains. This information was pulled from [https://docs.google.com/document/d/1YnlB6JTVk2sxe_uO2sGf5-uRQneSnvMeTPXAlpPnZEs/edit?usp=sharing here.]
  
 
<h1>Supported NMEA Parameter Group Messages</h1>
 
<h1>Supported NMEA Parameter Group Messages</h1>
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The documents clearly state that the OEM 719 uses the NMEA 2000 standard over the old NMEA 0183. But later refers to versions 3.10 and 4.10 which are versions of the NMEA 0183 standard. It also references “sentences” which I thought existed on NMEA 0183 and older versions, however, I may be mistaken and sentences may be a subsection of PGN’s.  Once we receive our first GNSS solution data it should become clear. I have included information on these sentences below.
 
The documents clearly state that the OEM 719 uses the NMEA 2000 standard over the old NMEA 0183. But later refers to versions 3.10 and 4.10 which are versions of the NMEA 0183 standard. It also references “sentences” which I thought existed on NMEA 0183 and older versions, however, I may be mistaken and sentences may be a subsection of PGN’s.  Once we receive our first GNSS solution data it should become clear. I have included information on these sentences below.
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 +
<h1>NMEA Sentences</h1>
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NMEA sends a line of data called a sentence that is totally self contained and independent from other sentences. There are standard sentences for each device category and there is also the ability to define proprietary sentences for use by the individual company. All of the standard sentences have a two letter prefix that defines the device that uses that sentence type. (For gps receivers the prefix is GP.) which is followed by a three letter sequence that defines the sentence contents. Each sentence begins with a '$' and ends with a carriage return/line feed sequence and can be no longer than 80 characters of visible text (plus the line terminators). The data is contained within this single line with data items separated by commas.
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This is not a full list, I only included ones that seemed relevant.
 +
More sentences can be found [http://www.gpsinformation.org/dale/nmea.htm here.]
 +
 +
<h2>GGA</h2>
 +
Essential fix data which provide 3D location and accuracy data.
 +
Eg: $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
 +
 +
<h2>GSA</h2>
 +
GPS DOP and active satellites. This sentence provides details on the nature of the fix. It includes the numbers of the satellites being used in the current solution and the DOP. DOP (dilution of precision) is an indication of the effect of satellite geometry on the accuracy of the fix. It is a unitless number where smaller is better. For 3D fixes using 4 satellites a 1.0 would be considered to be a perfect number, however for overdetermined solutions it is possible to see numbers below 1.0.
 +
Eg: $GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39
 +
 +
<h2>GSV</h2>
 +
Satellites in View shows data about the satellites that the unit might be able to find based on its viewing mask and almanac data. It also shows current ability to track this data. Note that one GSV sentence only can provide data for up to 4 satellites and thus there may need to be 3 sentences for the full information. It is reasonable for the GSV sentence to contain more satellites than GGA might indicate since GSV may include satellites that are not used as part of the solution. It is not a requirement that the GSV sentences all appear in sequence. To avoid overloading the data bandwidth some receivers may place the various sentences in totally different samples since each sentence identifies which one it is.
 +
Eg: $GPGSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75
 +
 +
<h2>VTG</h2>
 +
Velocity made good.
 +
Eg: $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48
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 +
<h2>RMC</h2>
 +
NMEA has its own version of essential gps pvt (position, velocity, time) data. It is called RMC, The Recommended Minimum
 +
Eg: $GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A
 +
 +
<h2>AAM</h2>
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Waypoint Arrival Alarm is generated by some units to indicate the Status of arrival (entering the arrival circle, or passing the perpendicular of the course line) at the destination waypoint.
 +
Eg: $GPAAM,A,A,0.10,N,WPTNME*32
 +
 +
<h2>ALM</h2>
 +
GPS Almanac Data contains GPS week number, satellite health and the complete almanac data for one satellite. Multiple messages may be transmitted, one for each satellite in the GPS constellation, up to maximum of 32 messages. Note that these sentences can take a long time to send so they are not generally sent automatically by the gps receiver. Note that this sentence breaks the 80 character rule. Also note that this sentence is often accepted as input so that you can preload a new almanac in a receiver.
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Eg: $GPALM,A.B,C.D,E,F,hh,hhhh,...
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<h2>ZDA</h2>
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Data and Time
 +
Eg:
 +
$GPZDA,hhmmss.ss,dd,mm,yyyy,xx,yy*CC
 +
$GPZDA,201530.00,04,07,2002,00,00*60

Latest revision as of 13:28, 5 June 2019

The OEM 719 outputs the data collected after the receiver does it's calculations in the NMEA2000 format by default. NMEA2000 messages are sent as packets that consist of a header followed by (typically) 8 bytes of data. The header for a message specifies the transmitting device, the device to which the message was sent (which may be all devices), the message priority, and the PGN (Parameter Group Number). The PGN indicates which message is being sent, and thus how the data bytes should be interpreted to determine the values of the data fields that the message contains. This information was pulled from here.

Supported NMEA Parameter Group Messages

OEM7 receivers support the following NMEA2000 Parameter Group Messages (PGN) over the CAN bus.

PGN 126992 System Time

The purpose of this PGN is twofold: To provide a regular transmission of UTC time and date. To provide synchronism for measurement data.

PGN 129025 GNSS Position Rapid Update

This PGN provides latitude and longitude referenced to WGS84. Being defined as single frame message, as opposed to other PGNs that include latitude and longitude and are defined as fast or multi-packet, this PGN lends itself to being transmitted more frequently without using up excessive bandwidth on the bus for the benefit of receiving equipment that may require rapid position updates.

PGN 129026 COG & SOG Rapid Update

This PGN is a single frame PGN that provides Course Over Ground (COG) and Speed Over Ground (SOG).

PGN 129027 Position Delta High Precision Rapid Update

The "Position Delta, High Precision Rapid Update" Parameter Group is intended for applications where very high precision and very fast update rates are needed for position data. This PGN can provide delta position changes down to 1 millimeter with a delta time period accurate to 5 milliseconds.

PGN 129029 GNSS Position

This PGN conveys a comprehensive set of Global Navigation Satellite System (GNSS) parameters, including position information.

PGN 129551 GNSS Differential Signal

GNSS differential correction receiver status tagged by sequence ID. Status information includes frequency, SNR, and use as a correction source.

The documents clearly state that the OEM 719 uses the NMEA 2000 standard over the old NMEA 0183. But later refers to versions 3.10 and 4.10 which are versions of the NMEA 0183 standard. It also references “sentences” which I thought existed on NMEA 0183 and older versions, however, I may be mistaken and sentences may be a subsection of PGN’s. Once we receive our first GNSS solution data it should become clear. I have included information on these sentences below.

NMEA Sentences

NMEA sends a line of data called a sentence that is totally self contained and independent from other sentences. There are standard sentences for each device category and there is also the ability to define proprietary sentences for use by the individual company. All of the standard sentences have a two letter prefix that defines the device that uses that sentence type. (For gps receivers the prefix is GP.) which is followed by a three letter sequence that defines the sentence contents. Each sentence begins with a '$' and ends with a carriage return/line feed sequence and can be no longer than 80 characters of visible text (plus the line terminators). The data is contained within this single line with data items separated by commas.

This is not a full list, I only included ones that seemed relevant. More sentences can be found here.

GGA

Essential fix data which provide 3D location and accuracy data. Eg: $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47

GSA

GPS DOP and active satellites. This sentence provides details on the nature of the fix. It includes the numbers of the satellites being used in the current solution and the DOP. DOP (dilution of precision) is an indication of the effect of satellite geometry on the accuracy of the fix. It is a unitless number where smaller is better. For 3D fixes using 4 satellites a 1.0 would be considered to be a perfect number, however for overdetermined solutions it is possible to see numbers below 1.0. Eg: $GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39

GSV

Satellites in View shows data about the satellites that the unit might be able to find based on its viewing mask and almanac data. It also shows current ability to track this data. Note that one GSV sentence only can provide data for up to 4 satellites and thus there may need to be 3 sentences for the full information. It is reasonable for the GSV sentence to contain more satellites than GGA might indicate since GSV may include satellites that are not used as part of the solution. It is not a requirement that the GSV sentences all appear in sequence. To avoid overloading the data bandwidth some receivers may place the various sentences in totally different samples since each sentence identifies which one it is. Eg: $GPGSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75

VTG

Velocity made good. Eg: $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48

RMC

NMEA has its own version of essential gps pvt (position, velocity, time) data. It is called RMC, The Recommended Minimum Eg: $GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A

AAM

Waypoint Arrival Alarm is generated by some units to indicate the Status of arrival (entering the arrival circle, or passing the perpendicular of the course line) at the destination waypoint. Eg: $GPAAM,A,A,0.10,N,WPTNME*32

ALM

GPS Almanac Data contains GPS week number, satellite health and the complete almanac data for one satellite. Multiple messages may be transmitted, one for each satellite in the GPS constellation, up to maximum of 32 messages. Note that these sentences can take a long time to send so they are not generally sent automatically by the gps receiver. Note that this sentence breaks the 80 character rule. Also note that this sentence is often accepted as input so that you can preload a new almanac in a receiver. Eg: $GPALM,A.B,C.D,E,F,hh,hhhh,...

ZDA

Data and Time Eg: $GPZDA,hhmmss.ss,dd,mm,yyyy,xx,yy*CC $GPZDA,201530.00,04,07,2002,00,00*60