Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 24-11-2010, 07:11   #1
Registered User

Join Date: Jul 2010
Posts: 51
NMEA Compass

Hi,

I have both a GPS and a compass connected to my computer. They are connected by USB (via serial converters). In Windows, they use two different serial ports. How can I use the NMEA stream from the compass? I do not want to use the compass data from the GPS.

Do I need to modify the source code? Where should I put these modifications? In nmea.cpp?
__________________

__________________
stensmo is offline   Reply With Quote
Old 24-11-2010, 09:36   #2
Registered User

Join Date: Feb 2010
Posts: 619
Hi stensmo...

I understand you wish to use HDG instead of COG for some purpose. What is the purpose and why?

Cheers,

Piotr
__________________

__________________
PjotrC is offline   Reply With Quote
Old 24-11-2010, 10:48   #3
Registered User

Join Date: Jul 2010
Posts: 51
Becasue the compass is more accurate than the gps at low speeds. I have a sail boat.


Quote:
Originally Posted by PjotrC View Post
Hi stensmo...

I understand you wish to use HDG instead of COG for some purpose. What is the purpose and why?

Cheers,

Piotr
__________________
stensmo is offline   Reply With Quote
Old 24-11-2010, 11:06   #4
Registered User

Join Date: Feb 2010
Posts: 619
stensmo...

True, a compass is more accurate as to where your bows does point, but not necessarily as to where your boat is actually sailing...

Most functions of a chartplotter, OCPN included, refer to actual or predicted geographical situation, which is more related to real Course Over Ground (currents and leeway included), rather than momentarily orientation of the vessel. If you like to use the HDG e.g. for coursekeeping, you might wish to configure e.g. OCPN to use the GPS NMEA port for COG and another tool, like PolarCOM, to display the HDG, coming from another NMEA port, completely independent of OCPN. Then you will have the best of both worlds.

I do not think this is a case for modifying any source code .

Cheers,

Piotr
__________________
PjotrC is offline   Reply With Quote
Old 24-11-2010, 12:10   #5
Registered User

Join Date: Jul 2010
Posts: 51
I use the "course up" mode, so I want the map to reflect my current heading, even at low speeds.

The GPS now where it is regardless of the compass direction.

Quote:
Originally Posted by PjotrC View Post
stensmo...

True, a compass is more accurate as to where your bows does point, but not necessarily as to where your boat is actually sailing...

Most functions of a chartplotter, OCPN included, refer to actual or predicted geographical situation, which is more related to real Course Over Ground (currents and leeway included), rather than momentarily orientation of the vessel. If you like to use the HDG e.g. for coursekeeping, you might wish to configure e.g. OCPN to use the GPS NMEA port for COG and another tool, like PolarCOM, to display the HDG, coming from another NMEA port, completely independent of OCPN. Then you will have the best of both worlds.

I do not think this is a case for modifying any source code .

Cheers,

Piotr
__________________
stensmo is offline   Reply With Quote
Old 24-11-2010, 12:59   #6
Registered User

Join Date: Jul 2010
Posts: 51
I could implement the feature private to myself if anybody else does not want it. But people who have a compass would probably want to use the data for "course up" and the compass in the dashboard. COG is fine for everything else.
__________________
stensmo is offline   Reply With Quote
Old 24-11-2010, 13:52   #7
Registered User

Join Date: Feb 2010
Posts: 619
stensmo...

Having course-up display HDG- rather than COG-oriented is a valid request. Many systems implement this indeed. I do not know if this had been expressed before.

I myself am not a great HDG-UP fan for charts display, because of most unfavourable PC screen aspect in this direction, and maybe because of the habit of handling paper charts. However, in some cases of narrow pilotage, HDG-up probably may be helpful.

I tend to think yet another feature might be useful, where for example - knowing that my general course will be NE - I choose to have my boat always pinned down to near SW corner of the display, still having it North-up. Something that might be called "keep my boat here"...

You might probably start by looking for occurences of "cog" throughout the solution.

Cheers,
P.
__________________
PjotrC is offline   Reply With Quote
Old 24-11-2010, 17:10   #8
Registered User
 
Viking Sailor's Avatar

Join Date: Nov 2006
Location: San Francisco Bay
Boat: Fantasia 35 - s/v Feeling Good
Posts: 1,074
stensmo,

I understand that some NMEA multiplexers can be programmed to translate NMEA messages from one type to another. This might be another way to address this problem without having to modify OpenCPN.

__________________
Viking Sailor is online now   Reply With Quote
Old 25-11-2010, 11:57   #9
Registered User

Join Date: Jul 2010
Posts: 51
Thanks,

That was one option I had in mind. Are you talking about hardware multiplexers?

This problem can be solved by using software. Do you know of a software which can use NMEA data from two physical serial ports, do some translation and combine them into one serial port in Windows?



Quote:
Originally Posted by Viking Sailor View Post
stensmo,

I understand that some NMEA multiplexers can be programmed to translate NMEA messages from one type to another. This might be another way to address this problem without having to modify OpenCPN.

__________________
stensmo is offline   Reply With Quote
Old 25-11-2010, 19:29   #10
Registered User
 
Viking Sailor's Avatar

Join Date: Nov 2006
Location: San Francisco Bay
Boat: Fantasia 35 - s/v Feeling Good
Posts: 1,074
stensmo,

I don't know of any software that acts as a multiplexer. I was referring to hardware multiplexers.

__________________
Viking Sailor is online now   Reply With Quote
Old 25-11-2010, 22:00   #11
Marine Service Provider

Join Date: Feb 2010
Posts: 279
Software Multiplexer

SeaClear will accept data from up to 3 separate com ports. The datastream is multiplexed into a single stream and can be output by using SeaClear's Passthrough feature. You can daisychain separate instances of SeaClear to multiplex more inputs.
What OpenCPN does with the heading data I don't know

regards

Richard Fairman JP BA Author SeaClear Unleashed
__________________
r.fairman is offline   Reply With Quote
Old 26-05-2011, 20:25   #12
Registered User

Join Date: Jun 2008
Location: Fort Myers, FL
Boat: Rosborough 246
Posts: 2
Re: NMEA Compass

Franson at Franson - Quality software at affordable prices sells a software multiplexer for NMEA data. I use it to multiplex depth sounder readings and gps data. It is relatively inexpensive, somewhere around $30 US.
__________________
wd0d is offline   Reply With Quote
Old 27-05-2011, 03:14   #13
Registered User
 
Netsurfer's Avatar

Join Date: Jan 2010
Location: Cologne, Germany
Boat: Beneteau Oceanis 331
Posts: 557
Re: NMEA Compass

Quote:
Originally Posted by wd0d View Post
Franson at Franson - Quality software at affordable prices sells a software multiplexer for NMEA data. I use it to multiplex depth sounder readings and gps data. It is relatively inexpensive, somewhere around $30 US.
I guess you could have the same for free: XPort

Gunther
__________________
Deutschsprachige Community- und Support-Website unter OpenCPN.de
Netsurfer is offline   Reply With Quote
Old 27-05-2011, 08:00   #14
Marine Service Provider
 
bdbcat's Avatar

Join Date: Mar 2008
Posts: 4,880
Re: NMEA Compass

stensmo....

Currently, FWIW, the only thing that OCPN uses compass heading for is orientation of ownship icon.

Your request is valid, though. We really need more configurability on NMEA data sources and utilization.

We will get to it when resources allow.

How about a Feature Request for the Flyspray tracker?

Thanks
Dave
__________________
bdbcat is offline   Reply With Quote
Old 27-05-2011, 08:28   #15
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Re: NMEA Compass

Getting navigation software to recognize data coming from a number of comports can be a problem.

The solution is a NMEA multiplexer. We use one for our data storage computers and it works fine. We have numerous sources of NMEA data all of which must get recorded to these computers and a multiplexer is the only way for us to accomplish this.

With a multiplexer your HDG and your COG does not have to be a one or the other choice. You can have both going to an electronic chart which shows both a vector for your COG and your HDG.

I prefer North Up...Heading Up for me is disorienting with the chart constantly twisting around. This is obviously a personal preference with no right or wrong choice. Funny thing is I prefer heading up on the radar, probably because that is what I was brought up with before most radars were integrated with a compass. Although on larger vessels, north up was just as easy and required for doing radar plots.
__________________

__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Reply

Tags
compass, nmea

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
NMEA 2K and OpenCPN - How? sapster77 OpenCPN 18 13-03-2013 12:29
NMEA 0183 v. 1.5 vs 1.8 bchaps Marine Electronics 3 03-03-2010 17:06
NMEA interface for Ritchie Magtronic fluxgate compass PaulSommers Marine Electronics 2 16-01-2008 04:23
The NMEA Mystery Sandero Marine Electronics 18 21-06-2006 20:20
Compass Deviatrion-Compass Card Paul Bradbury General Sailing Forum 6 05-02-2006 15:34



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 15:17.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.