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Old 29-03-2017, 01:02   #1
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Open CPN Lat Lon Incorrect

I've loaded unified charts onto Open CPN and found that the Lat Lon puts me about 20 miles north of my actual location. I have confirmed this in two ways

1. Connected GPS which locates me 20 miles north of my actual location. The actual GPS lat and lon are correct, but it places me 20 miles north on the map.
2. put the cursor/cross hair over my location which gives me lat lon for 20 miles south of my location. Lat Lon given by Open CPN typed into google maps puts me 20 miles south of my location.

Hope this makes sense.

Is there a way of calibrating the charts to the Open CPN software or is there a box i haven't ticked. Speaking to a technical department would really help as my computer skills aren't great and I tend lose patience with it all.

Thanks in advance for any help offered

Regards

Lee
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Old 29-03-2017, 01:12   #2
Moo
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Re: Open CPN Lat Lon Incorrect

Quote:
Originally Posted by leegray88 View Post
I've loaded unified charts onto Open CPN and found that the Lat Lon puts me about 20 miles north of my actual location. I have confirmed this in two ways
Sounds like a projection / calibration issue.

What are unified charts?

What is the source of your charts?

What projection are your charts?

Is the GPS sending the location to your computer in WGS84?

And where are you? Perhaps there is a bug at your location?
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Old 29-03-2017, 05:42   #3
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Re: Open CPN Lat Lon Incorrect

Thanks for the reply

What are unified charts? Rasta Charts that have been purchased via visitmyharbour.com - I don't think this is the issue because Open CPN has this probelem without the charts laoded

What is the source of your charts? via a virtual DVD drive , but the charts are also available on a USB stick

What projection are your charts? all different projections but as stated above probably not relevant

Is the GPS sending the location to your computer in WGS84? Not sure, but the Lat long is incorrect on Open CPN without GPS sending its NMEA 0183

And where are you? Perhaps there is a bug at your location? Based in London. Other software, Google, Navionics provides correct Lat Lon
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Old 29-03-2017, 05:50   #4
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Re: Open CPN Lat Lon Incorrect

You could try making a Google earth chart from here, see if that puts you in the right place...



https://www.venturefarther.com
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Old 29-03-2017, 05:57   #5
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Re: Open CPN Lat Lon Incorrect

Thanks. But i'd like this system to work Many people use it and (when it works) i think will be a great navigation tool.
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Old 29-03-2017, 06:16   #6
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Re: Open CPN Lat Lon Incorrect

Could you take a screenshot (even with a phone), with the boat on screen, the gps connected and the bottom bare visible (where there's the position)?

20 miles..., what unit are you using for lat/lon? could be a decimal degrees/degrees minutes seconds misunderstanding, on the other hand the gps shouldn't care, if it's working.
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Old 29-03-2017, 06:20   #7
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Re: Open CPN Lat Lon Incorrect

Literally just had the same thought. I will take a picture when at home and upload.
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Old 29-03-2017, 06:32   #8
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Re: Open CPN Lat Lon Incorrect

I've done some further digging and i think the GPS coordinates are being interpreted as degrees dms, which is putting me in the wrong place. I'm using the GPS on my phone and bluetoothing it to the PC which Open CPN then reads in Degrees dms (i think). I've just tested this on google maps but need to confirm on Open CPN. If i'm right i will need to work out how to get Open CPN to read GPS coordinates directly instead of dms.
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Old 29-03-2017, 06:32   #9
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Location: Probably in an anchorage or a boatyard..
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Re: Open CPN Lat Lon Incorrect

Quote:
Originally Posted by leegray88 View Post
Thanks. But i'd like this system to work Many people use it and (when it works) i think will be a great navigation tool.
If the Google earth chart works then that suggests the problem is possibly with the VMH charts somehow, might help with troubleshooting.
BTW, up to date uk vector charts are available now as well -
oeSENC - o-charts
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Old 29-03-2017, 12:39   #10
Moo
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Re: Open CPN Lat Lon Incorrect

Quote:
Originally Posted by leegray88 View Post
I've done some further digging and i think the GPS coordinates are being interpreted as degrees dms, which is putting me in the wrong place. I'm using the GPS on my phone and bluetoothing it to the PC which Open CPN then reads in Degrees dms (i think). I've just tested this on google maps but need to confirm on Open CPN. If i'm right i will need to work out how to get Open CPN to read GPS coordinates directly instead of dms.
You said earlier that you were getting the wrong position indicated on your chart with or without GPS connected. You said that the cursor is giving the wrong lat/lon. i.e. the charts are geo-referenced incorrectly.

You need to get the charts correctly geo-referenced so that the cursor gives you the correct location before you worry about the GPS at all.

Lets see you screenshots and then take it from there. Google Earth as suggested would be a useful test.
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Old 30-03-2017, 03:03   #11
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Re: Open CPN Lat Lon Incorrect

I tried another way yesterday and installed a NMEA 0183 to USB cable (see link) which takes a signal directly from my old Garmin GPS 120 and plots me on the OPEN CPN on my lap top...worked perfectly first time. Physical install less than 5 minutes, software install less than 10 minutes.
I've also changed the measurement value in OPEN CPN which will probably solve my original problem, but didn't get a chance to test as my girlfriend wanted to go shopping

Digital Yacht - USB TO NMEA ADAPTOR

Thanks for all replies and help especially did-g whom got me thinking.

Quote:
Originally Posted by did-g View Post
Could you take a screenshot (even with a phone), with the boat on screen, the gps connected and the bottom bare visible (where there's the position)?

20 miles..., what unit are you using for lat/lon? could be a decimal degrees/degrees minutes seconds misunderstanding, on the other hand the gps shouldn't care, if it's working.
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