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Old 17-06-2020, 22:16   #1
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nmea message not plotting correctly

v 5.0.0+9065270- Win10 Pro


I am inputting the following nmea message:


<GREEN>15:11:16 (UDP:localhost:5000) $GPRMC,182623.00,A,3780.70,S,14497.00,E,2,70,07062 0,0.0,E*7B<0x0D><0x0A>
as shown in the NMEA Debug Window.


However it plots on the chart at -38.344873 145.616667.


Why????
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Old 18-06-2020, 03:33   #2
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Re: nmea message not plotting correctly

Quote:
3780.70,S,14497.00,E
'37 80.7S' and '144 97.0E' are clearly in error. '07062 0' should not have a space.

What is your NMEA source?

Mike
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Old 18-06-2020, 03:57   #3
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Re: nmea message not plotting correctly

https://gpsd.gitlab.io/gpsd/NMEA.htm...on_information

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Old 18-06-2020, 05:09   #4
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Re: nmea message not plotting correctly

The 3780.70,S,14497.00,E in degrees and decimal minutes in your NMEA data does indeed convert to -38.344873 145.616667 in decimal degrees. So OpenCPN has done the best it can with the faulty data it has been given!
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Old 18-06-2020, 10:13   #5
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Re: nmea message not plotting correctly

FYI here is a sample RMC sentence that OpenCpn seems to decode correctly.


$GPRMC,170347.00,A,5238.62552,N,00713.34533,W,0.57 1,,180620,,,A*67


Location is about 52 degrees 38.6 minutes north, 7 degrees 13.3 mins west.
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Old 18-06-2020, 10:37   #6
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Re: nmea message not plotting correctly

Quote:
Originally Posted by MikadoII View Post
...$GPRMC,182623.00,A,3780.70,S,14497.00,E,2,70,07 0620,0.0,E*7B<0x0D><0x0A>
as shown in the NMEA Debug Window...
RMC expects latitude in DDMM.MM format and longitude in DDDMM.MM format. So, as noted above, your sentence is saying 3780.7'S and 14497.00'E. I suspect the vendor of whatever is supplying the data meant 37.807S and 144.97E but that's not how the standard is written.

Quote:
Originally Posted by Rasbats View Post
'37 80.7S' and '144 97.0E' are clearly in error. '07062 0' should not have a space.

What is your NMEA source?

Mike
@Mike, the forum adds a space to NMEA sentences > 50 characters in length when posting them. The only way to avoid this is to use code tags, quote tags and plain text don't work. And you can't edit them out, if you go to edit a string the space isn't there, it is only a part of the display side of things. I edited the space out of the OP's NMEA string, here is it posted three ways (posted all three items without the space).

Code:
$GPRMC,182623.00,A,3780.70,S,14497.00,E,2,70,070620,0.0,E*7B<0x0D><0x0A>
Quote:
$GPRMC,182623.00,A,3780.70,S,14497.00,E,2,70,07062 0,0.0,E*7B<0x0D><0x0A>
$GPRMC,182623.00,A,3780.70,S,14497.00,E,2,70,07062 0,0.0,E*7B<0x0D><0x0A>

I've had a couple of go-arounds with the forum management, the bottom line is when troubleshooting NMEA sentences if there is a space at character 50 it is probably a phantom of this forum. Getting everyone to use code tags is going to be difficult.
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Old 19-06-2020, 01:55   #7
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Re: nmea message not plotting correctly

Thanks everyone for your comments. I am using a GPS (and other data) device which uploads to ThingSpeak. I am then using node-red to extract lat & long from ThingSpeak and inputting it to OpenCPN. My problem has been to pin down the formats used by ThingSpeak and Open CPN. The actual strings I have quoted are just a line of text in node-red inserted for testing purposes. Rasbats points to the format for an RMC sentence but it doesn't spell out the format of the lat or long value. Dsanduril spells out the RMC format specifically. Thanks. I presume that "decimal degrees" is degree and the decimal part of a degree that the minutes and seconds constitute. The extra space is just a distraction. Thanks again.
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