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Decoding of NMEA signals (Part 2)

Decoding of NMEA signals (Part 2)

27.05.2014

Read the first part of the article.

RMC (Recommended Minimum Specific GPS Data) - recommended minimum data from the GPS

Standard IEC 61162-1, 2000.

Contains: time, date, position, course and speed derived from the receiver-GPS.

$ - RMC, hhmmss.ss1, A2, llll.ll3, a4, yyyyy.yy5, a6, x.x7, x.x8, xxxxxx9, x.x10, a11, a12 * hh <CR> <LF>.

N

Field

Title

Value

Note

1

hhmmss.ss

UTC time of observation

Hours, minutes, seconds

not processed

2

A

Status data

'A' - reliable data; 
'V' - unreliable data

 

3

llll.ll

Latitude

Degrees, minutes and tenths of minutes

 

4

a

Hemisphere

'N' - the north; 
'S' - South

 

5

yyyyy.yy

Longitude

Degrees, minutes and tenths of minutes

 

6

a

Hemisphere

'E' - the east; 
'W' - Western

 

7

xx

Speed over ground (knots)

 

 

8

xx

True course over ground - track angle (in degrees)

 

 

9

xxxxxx

Date (ddmmyy)

 

not processed

10

xx

Magnetic declination

 

not processed

11

a

Hemisphere

'E' - the east;

'W' - Western

not processed

12

a

Positioning system mode indicator

'A' - Autonomous mode;

'D' - Differential mode;
'E' - Estimated (dead reckoning) mode;
'M' - Manual input mode;
'S' - Simulator mode;
'N' - Data not valid

not processed

RSD (Radar System Data) - LLS

Standard IEC 61162-1, 2000 IMO Resolution A.810, 1995 and MSC 64 (67)

Annex 4: Radar display setting data.

$ - RSD , xx 1 , xx 2 , xx 3 , xx 4 , xx 5 , xx 6 , xx 7 , xx 8 , xx 9 , xx 10 , xx 11 , a 12 , A 13 * HH <CR> <LF >

N

Field

Title

Value

Note

1

xx

Distance reference point number 1

Reference point number 1 are located at the distance and bearing from your vessel and is equipped with an independent electronic ruler

 

2

xx

Bearing reference point number 1 is (degrees)

See above

 

3

xx

Electronic distance line number 1

(VRM1)

 

4

xx

E bearing line number 1 (in degrees)

(EBL1)

 

5

xx

Distance reference point number 2

Reference point number 2 is at the specified distance and bearing from your vessel and is equipped with an independent electronic ruler

 

6

xx

The bearing starting point number 2 (degrees)

See above

 

7

xx

Electronic distance line number 2

(VRM2)

 

8

xx

E bearing line number 2 (in degrees)

(EBL2)

 

9

xx

Distance to the cursor from your vessel

 

 

10

xx

Bearing pad (degrees)

 

 

11

xx

Applicable range scale

 

not processed

12

A

Pdinitsy ranging

'K' - km, 
'N' - mor. mile, 
'S' - statute miles

 

13

A

Display Orientation

'C' - 'rate'; 
'H' - 'orientation to the center plane'; 
'N' - 'north'

not processed

 

SNU (Loran-C SNR Status) - relationship status signal-to-interference Loran-C

Standard NMEA 0183 v.2.1, 1995 (not recommended for new designs).
Warning about the critical value of the ratio level of Loran-C signal to noise, is used to indicate that the position and other navigation data unreliable.
$ - SNU, A 1 * hh <CR> <LF>.
 

N

Field

Title

Value

Note

1

A

Status data

'A' - reliable data; 
'V' - unreliable data

 

TTM (Tracked Target message) - bug tracking goals

Standard IEC 61162-1, 2000 IMO Resolution A.820, 1995 and MSC 64 (67)

Annex 4: Data associated with a tracked target relative to own ship's position.

Contains information about the monitored targets in relation to the position of his vessel.

$ - TTM, xx 1 , xx 2 , xx 3 , a 4 , xx 5 , xx 6 , n 7 , xx 8 , xx 9 , a 10 , c-c 11 , a 12 , a 13 , hhmmss.ss 14 , a 15 * hh <CR> <LF>.

N

Field

Title

Value

Note

1

xx

Target number

 

 

2

xx

Distance to target

 

 

3

xx

Bearing from own ship (degrees)

 

 

4

a

Type of bearing

'T' - true; 
'R' - the relative

 

5

xx

Target speed

 

 

6

xx

Target course (degrees)

 

 

7

n

Type of course

'T' - true; 
'R' - the relative

 

8

xx

CPA (in miles)

Distance of closest-point-of-approach

 

9

xx

TCPA (in min.)

Time to distance of closest-point-of-approach

'Minus' = increased

10

a

U measuring speed / distance

'R' - km; 
'N' - mor. mile; 
'S' - statute miles

 

11

c-c

Name of target

 

not processed

12

a

Status goals

 

 

13

a

Purpose-binding

 

not processed

14

hhmmss.ss

UTC time

 

not processed

15

a

Type of seizure

 

not processed

VBW (DUAL Ground / Water Speed) - speed over ground and water

Standard IEC 61162-1, 2000.

Contains the X and Y components of the velocities with respect to water and soil.

$ - VBW,, xx 1 , xx 2 , a 3 , xx 4 , xx 5 , a 6 , xx 7 , a 8 , xx 9 , a 10 * hh <CR> <LF>.

N

Field

Title

Value

Note

1

xx

The longitudinal component of the water speed (knots)

 

negative aft

2

xx

Transverse component of the water speed (knots)

 

negative to the left side

3

A

Status data

'A' - reliable data; 
'V' - unreliable data

 

4

xx

The longitudinal component of the velocity over ground (knots)

 

negative aft

5

xx

The transverse component of the velocity over ground (knots)

 

negative to the left side

6

A

Status data

'A' - reliable data; 
'V' - unreliable data

 

7

xx

Stern transverse water speed (knots)

 

not processed

8

A

Status data

'A' - reliable data; 
'V' - unreliable data

not processed

9

xx

Stern transverse ground speed (knots)

 

not processed

10

A

Status data

'A' - reliable data; 
'V' - unreliable data

not processed

Attention!

When you receive a message, the following priorities VBW processing fields:

  1. check the status of field number 6.
  2. treatment values in the number 4.
  3. obtaining the velocity relative to the ground processing values in the number 5.
  4. check the status of field number 3.
  5. treatment values in the number 1.
  6. obtaining the velocity relative to the water treatment values in the number 2.

 

VHW (Water Speed and Heading) - the speed and course of the vessel relative to the water

Standard IEC 61162-1, 2000.

$ - VHW, xx 1 , t 2 , xx 3 , m 4 , xx 5 , n 6 , xx 7 , k 8 * hh <CR> <LF>.

N

Field

Title

Value

Note

1

xx

Rates (in degrees)

 

 

2

 

Type

'T' - true

 

3

xx

Rates (in degrees)

 

not processed in 3000 ns ecdis

4

m

Type

'M' - magnetic

not processed in 3000 ns ecdis

5

xx

Speed

 

 

6

n

Units

'N' - nodes

 

7

xx

Speed

 

not processed

8

k

Units

'K' - km / h

not processed

VTG (Course Over Ground and Ground Speed) - course and speed over ground

Standard IEC 61162-1, 2000.

$ - VTG, xx 1 , t 2 , xx 3 , m 4 , xx 5 , n 6 , xx 7 , k 8 , a 9 * hh <CR> <LF>.

&

N

Field

Title

Value

Note

1

xx

Course over ground (degrees)

 

 

2

t

Type

'T' - true

 

3

xx

Magnetic heading (degrees)

 

not processed

4

m

Type

'M' - magnetic

not processed

5

xx

Speed

 

 

6

n

Units

'N' - nodes

 

7

xx

Speed

 

not processed


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