Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 02-08-2014, 07:31   #226
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

Inside the Plugin there is and Information Html documentation I know we are not writing a How to here, but perhaps NAV could review it?
Following are some of the possible inclusions in that documentation.(Celestial Navigation_pi > Celestial Navigation Sights menu > Information.

Also, separately, we should probably be updating Cnav Plugin documentation on the Opencpn.org website... There does not seem to be documentation for using Cel Nav on the Plugins page here...
Plugins | Official OpenCPN Homepage - Cel Nav does not appear
Celestial Navigation | Official OpenCPN Homepage -here a result of search, which is a begining.
Celestial Navigation PlugIn | Official OpenCPN Homepage - Old note
http://opencpn.org/ocpn/node/143 - Supplimentary Software
PlugIns | Official OpenCPN Homepage - Download page
I will look at this in the next couple of days. NAV if you can help with any suggestions, write-ups, links or editing. Please advise. (You can register yourself to be an editor, and then login and edit. If you want to..)User account | Official OpenCPN Homepage I will pull some of this together into a Cel Nav Plugin page and get it started..

Quote:
Standard practice in navy and merchant navy with regard to celestial positioning is as follows (assuming no artificial horizon is available on the sextant):
  • During morning nautical twilight (about 15 minutes): if possible take 6 star/planet observations.
  • In the morning at about 09:00LT: take a sun's observation (later to be shifted to noon-time).
  • At local noon: take a sun's observation (traditionally only direct latitude calculation from sun at meridian passage). Construct a fix for noon from both sun observations.
  • During evening nautical twilight (about 15 minutes): if possible take 6 star/planet observations.
  • Use moon for an observation in above practice when situation permits.
Quote:
Digital Nautical Almanac on the web. It's from 1994. Link: http://reednavigation.com/files/Naut...manac-1994.pdf
__________________

__________________
rgleason is offline   Reply With Quote
Old 02-08-2014, 08:13   #227
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

I've reconnected the orginal page and made some prelim edits to be more accurate. Will be getting screenshots and better documentation together. Any help, writeups, procedures would be most appreciated! If NAV could review this page and advise on inaccuracies and improvements it would be great.
Celestial Navigation PlugIn | Official OpenCPN Homepage
I will try to incorporate what Sean has under the Information Tab as well.

Thanks.
__________________

__________________
rgleason is offline   Reply With Quote
Old 03-08-2014, 01:34   #228
NAV
Registered User

Join Date: Sep 2010
Location: Netherlands
Posts: 410
Re: Celestial Navigation Plugin Redux

Quote:
Originally Posted by rgleason View Post
NAV if you can help with any suggestions, write-ups, links or editing. Please advise.
I suggest to base the general theory on the document found here (say chapters 1 to 3): http://www.celnav.de/page2.htm . And perhaps partly on information from Bowditch and the Nautical Almanac.

The actual theory and computation methods to calculate a fix from reduced measurements used in the plugin should initially be written by Sean I think. It's an innovative method of which only he knows the background en details. When I look at the code (which I understand only marginally, I still have some questions; I'll write these down later.)
__________________
NAV is offline   Reply With Quote
Old 03-08-2014, 02:08   #229
NAV
Registered User

Join Date: Sep 2010
Location: Netherlands
Posts: 410
Re: Celestial Navigation Plugin Redux

Two more documents with test results. Another one for a comparison of altitude reduction, and one for a comparison between the direct computation method for a fix as explained in the Nautical Almanac (1994, pages 283 para 12 and page 283), and the fix results of the plugin.
Attached Files
File Type: doc Nautical Almanac Alt Reduction 2004.doc (60.0 KB, 34 views)
File Type: doc Direct comp.doc (40.0 KB, 30 views)
__________________
NAV is offline   Reply With Quote
Old 03-08-2014, 07:13   #230
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

Nautical Almanac 2004
Looks like H apparent is good. Is there some difference in the way
H Observed is calculated? --Something to do with Refraction, Parallex, Par.in Alt. or SD?

Direct Comp
I'll let Sean respond. I don't know enough yet.
Thank you for the good links on General Theory.
__________________
rgleason is offline   Reply With Quote
Old 03-08-2014, 12:16   #231
Registered User
 
boat_alexandra's Avatar

Join Date: Aug 2009
Location: grenada
Boat: bristol 27
Posts: 2,556
Re: Celestial Navigation Plugin Redux

Quote:
Originally Posted by rgleason View Post
Nautical Almanac 2004
Looks like H apparent is good. Is there some difference in the way
H Observed is calculated? --Something to do with Refraction, Parallex, Par.in Alt. or SD?
Refraction varies with temperature and pressure.

I would like to compare the values the plugin uses for refraction, parallex, and limb correction to the almanac test data.

Also would like to compare the geographical position. So far from the data NAV has posted, the differences in Ho are much smaller than the measurement error of reading a sextant.

Also consider my models are more recent and probably more accurate.
Quote:
Direct Comp
I'll let Sean respond. I don't know enough yet.
Thank you for the good links on General Theory.
Maybe a separate dialog for this one? It would be good to offer the current methods as well as the more traditional LOP methods. The simplest is by using linear least squares for each celestial body. This method can be iterated several times to converge on the fix. It would be good to figure out how to display computations, and even plot the actual lines as a learning tool for teaching traditional celestial navigation.
__________________
boat_alexandra is offline   Reply With Quote
Old 03-08-2014, 18:45   #232
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

I've started adding to Celestial Nav Plugin Docs here, others are welcome to edit and add. I have plans to add NAV's links and the original sightings he listed, for reference.
Also I will format it better and try to complete the process more completely.
Celestial Navigation PlugIn | Official OpenCPN Homepage

Right now I am having trouble getting this page to show up in the documentation.
Why?
__________________
rgleason is offline   Reply With Quote
Old 04-08-2014, 08:23   #233
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

Documentation: The page is now showing in Plugins secton. I had to go down to the bottom while editing the page and select "Book Outline" and set the priority "-13" and pick the parent directory "Plugins". Now it shows in the Plugins list! Plugins | Official OpenCPN Homepage
I had not placed it in the Contents Index.
__________________
rgleason is offline   Reply With Quote
Old 04-08-2014, 10:18   #234
NAV
Registered User

Join Date: Sep 2010
Location: Netherlands
Posts: 410
Re: Celestial Navigation Plugin Redux

Quote:
Originally Posted by boat_alexandra View Post
I would like to compare the values the plugin uses for refraction, parallex, and limb correction to the almanac test data.
Also would like to compare the geographical position. So far from the data NAV has posted, the differences in Ho are much smaller than the measurement error of reading a sextant.
Also consider my models are more recent and probably more accurate.
Accuracy of data in the printed Nautical Almanacs:
The largest error that can occur in GHA and declination of any body other than the Sun or Moon is less than 0.2'; it may reach 0.25' for the Sun and 0.3' for that of the Moon. In practice it may be expected that only one third of the values of GHA and declination will have errors larger than 0.05', and less than one tenth will have errors larger than 0.1'.

The errors in the altitude corrections are nominally in the same order (but the actual values of dip and refraction at low altitudes may differ considerably in extreme atmospheric conditions).

Depending on the type of sextant, the reading accuracy of the sextant can be 0.2', 0.1' or 10". Measurement and reading errors made by the navigator will be larger ...
__________________
NAV is offline   Reply With Quote
Old 04-08-2014, 10:55   #235
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

Ok the Cel Nav plugin Documentation has been updated.
http://opencpn.org/ocpn/celestial_navigation_plugin

Please review and advise on any problems, errors inaccuracies, bad links.

Also just a question, out of curiosity is NAV Henning Umland?

__________________
rgleason is offline   Reply With Quote
Old 04-08-2014, 11:38   #236
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

From celnav.de Page 13-3 http://www.celnav.de/page2.htm
Quote:
For great circle navigation, the gnomonic projection offers the advantage that any great circle appears as a straight
line. Rhumb lines, however, are curved. A gnomonic chart is obtained by projecting each point on the earth’s surface
from the earth’s center to a plane tangent to the surface.
Are gnomonic charts able to be created from spheric on a computer?
Maybe this chart would help with time offset, if it is easy to make and use this type of chart?
__________________
rgleason is offline   Reply With Quote
Old 04-08-2014, 11:50   #237
NAV
Registered User

Join Date: Sep 2010
Location: Netherlands
Posts: 410
Re: Celestial Navigation Plugin Redux

Quote:
Originally Posted by rgleason View Post
Also just a question, out of curiosity is NAV Henning Umland?
No, certainly not :-). Henning Umland is a scientist. I'm only an ex-navigator (merchant navy, navy, naval air department).
__________________
NAV is offline   Reply With Quote
Old 04-08-2014, 12:40   #238
NAV
Registered User

Join Date: Sep 2010
Location: Netherlands
Posts: 410
Re: Celestial Navigation Plugin Redux

Attached descriptions from Andres Ruiz of modern calculation methods in astronomical positioning may also be interesting. ( https://sites.google.com/site/navigationalalgorithms/papersnavigation)
Attached Files
File Type: pdf SRmatrix.en.pdf (458.9 KB, 21 views)
File Type: pdf vectorialEquationCOP.en.pdf (582.6 KB, 35 views)
__________________
NAV is offline   Reply With Quote
Old 08-08-2014, 08:48   #239
NAV
Registered User

Join Date: Sep 2010
Location: Netherlands
Posts: 410
Re: Celestial Navigation Plugin Redux

Quote:
Originally Posted by rgleason View Post
I know we are not writing a How to here, but perhaps NAV could review it?
Done. I made some textual changes and additions.
__________________
NAV is offline   Reply With Quote
Old 08-08-2014, 20:25   #240
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 7,829
Re: Celestial Navigation Plugin Redux

Thanks Nav. very much. Should we also add your last two refs?
__________________

__________________
rgleason is offline   Reply With Quote
Reply

Tags
celestial navigation, navigation

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
Logbook Konni for OpenCPN konni OpenCPN 819 18-11-2016 02:31
Google Earth Plugin r.fairman OpenCPN 417 15-02-2015 12:15
GRIB Weather Mark Ward OpenCPN 26 12-02-2012 22:33
Route Properties, Missing Functions James Baines OpenCPN 13 13-07-2011 05:31


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 22:47.


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.