Running Fix Postion Tool: Discussion

[rgleason]

Bob wrote:

Running fix position tool. When it comes down to it, when your boat is on the move, every sight (even those that are 1 minute apart) is a running fix. The nautical almanac shows examples where you take multiple sights while moving. You have a DR position for each sight. Then you take another sight for another body a few minutes later....and you are still moving. The nautical almanac describes a method to build a fix with those sites (page 283). You have to know your DR location for each of the sights. We only have 1 DR location in the Find Celestial Bodies. I'm thinking that we reference a DR location that is set in OPEN CPN core product and then when doing cel-nav, pull in that DR location.

There are several DR features in plugins.
Ocpn_Draw has a DR feature and there is a plugin named DR.
They do not have the control needed for this DR tool.

The javascript plugin has a script that Tony wrote for DR, it can readily be changed and adapted.
I might serve to be the beginning of a DR script that provides DR points for:

1. Noon Sun Sights: DR 20 minutes before and 20 minutes after Noon. Setting for time. An alarm 5 minutes before each sight. DR positions get entered into a DR List in Cel-Nav and linked to respective Sights?
2. Running DR's for running fixes?

[rgleason]

Tony [Antipole2] Javascript_pi author responded to my recent post on Cruisers Forum:

https://www.cruisersforum.com/forums/f134/javascript-plugin-v2-thread-after-25-jan-23-a-272422-2.html#post3979322

The modified . https://github.com/antipole2/Driver/tree/Next Note the extended capability for DR is in the Next branch, not main. See the About in the Next branch for what it does.

You could add alarms at certain times, as required.

Not sure about interfacing to the cel-nav plugin - I am not familiar with it.

As I recall, it does not play well with open-draw. That is something on my to-do list for next winter.

One simple way of interfacing is for one to write data to a file and the other to read it.

https://github.com/antipole2/JavaScript_pi/tree/master

Ocpn_draw has a DR feature as well
Ocpn_draw also communicates with Weather_routing and Watchdog using Odraw Messaging API See
https://opencpn-manuals.github.io/main/odraw/index.html#_integration_with_other_plugins

See https://opencpn-manuals.github.io/main/opencpn-dev/odraw-messaging.html

[rgleason]

From Bob

Ways Navigators reduce errors

• Take a run of sights (3 to 5) and selecting the best one to reduce. What I do is to input my run of sights into the plug-in, multi select the sights to see the lines of positions. Then, if one is way off, I won't use that rogue sight.

• Take the avg of a run of sights and use the average for sight reduction.
  Navigator loads all of his/her sights over time (at least 100), and determine their avg personal bias error.

• A navigator colleague of mine (ex US Navy), knows his avg error (Hs too high, or too low by decimal minutes). And then adjusts his sight to take into account his personal bias. You can load about 30 sights in the plug in. After 30, it gets a little dicey when you load the next sight. The plug in used to error out when you exceeded some limit. Now, it just hangs until the excess sights are deleted.

• The best way to minimize position errors is to do a 3 different body sight within 20 minutes (I think a few nights ago, Sun, Moon, and Venus made a good 3 body sight...it was too cold where I was). The 3 bodies should be spread apart. Enter the 3 body sights and time. When the plug in draws the line of positions, it will be a triangle. Your fix is in the center of the triangle. If your boat was moving while doing the 3 body fix (each fix has a DR location),

• You should be able to use the plug-in to advance the Line of position of the 1st and 2nd sight based on the distance traveled (60D = ST) to the 3rd sight's position. It is a fix if the 3 sights are made within 20 minutes, if more than 20 minutes, it is a running fix.

• When planning sights for the morning or evening, I like to draw a line (OCPN Draw) from my DR position to the bearing of the various bodies with altitude. Helps me plan the sights to be taken. And look for 2-3 body fix opportunities. Perhaps given a DR position, and knowing the date time, SOG and COG, the plugin could suggest potential sights to be taken over the next 24 hours.

[rgleason]

Also Astron User Notes .docx have illustrations on use of the Sight and Log Plotter page 26, also LLoP Lunar plotter on 18A/

See how Astron Program plots and graphs AP and fixes, see the tabs at the bottom. Sight and Log Plotter.

https://friendsofthevigilance.org.uk/Astron/Astron.html

In order to download Astron's comprehensive User Notes,
1: Copy (Ctrl-C) the below link.
2: Select a new browser tab and paste it (Ctrl-V) to the address bar.
3. Your browser will download the file to your downloads folder.

https://friendsofthevigilance.org.uk/Astron/AstronUserNotes.docx

We use the above indirect link method to avoid occasional browser security issues.
We suggest that you then save the file for easy future access.

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The following link accesses a folder from which you can ...
(a) Run a PowerPoint presentation explaining using Astron's main features
(b) Run a PowerPoint presentation explaining Lunar Lines of Position
(c) Download the entire Astron source code
https://drive.google.com/drive/folders/1-5b9b7ySW5hhXsd4ymlthsB_KHYZ1cqf?usp=sharing
The above PowerPoint presentations are not updated and some differences will be evident.

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You may also be interested in the writer's celestial navigation slide rule emulator programs.

TRADITIONAL BYGRAVE SLIDE RULE emulator.
https://friendsofthevigilance.org.uk/Astron/SlideRules/TraditionalBygrave/TraditionalBygrave.html

MODERN BYGRAVE SLIDE RULE emulator (C) Gary LaPook.
https://friendsofthevigilance.org.uk/Astron/SlideRules/ModernBygrave/ModernBygrave.html

CONVENTIONAL LINEAR SLIDE RULE emulator
https://friendsofthevigilance.org.uk/Astron/SlideRules/LinearSlideRule/SlideRule.html

[rgleason]