Plotting Questions; Radar ranges; magnetic compass bearings; positions on Open CPN...

[El Pinguino]

It would seem that some 4G radars have a thing called 'beam sharpening'. More from Panbo here-

'But note also how 4G’s “beam sharpening” is separating the ledge and buoy pair about a mile ahead. That’s very hard to do with the 5 degree beam width typical of an 18-inch radome.'


'https://panbo.com/simrad-broadband-radar-4g-hands-on-1/'

[st599]

Originally Posted by El Pinguino

I'm afraid anyone with a typical 'consumer grade' radar who thinks their radar will give them sub one degree bearing accuracy is kidding themselves.
This is from Furuno
'Azimuth Resolution
Suppose that two separate objects are in the same direction, at the same distance, from the boat from which you are looking. The resolution of a radar depends mainly on the horizontal beam width, so the narrower the beam width of an antenna, the higher the resolution of the radar. To increase the resolution of a Radar, we need to reduce the horizontal beam width, which can be accomplished with a larger antenna. There are X-band radars with antennas up to 3 meters wide, and in this case the angular beam width is 0.75 degrees, which is very important for accuracy. On the other hand, Radomes, with an antenna width of about 40cm, have an average horizontal beam width of 5.7°.
https://www.furuno.com/en/technology/radar/basic/

Combine this with the nature of most things you may choose to take a bearing from - with the exception of beacons - and radar bearings are a sub par way of fixing your position.
This is from Panbo- a Navico Halo 24 display.

https://panbo.com/wp-content/uploads...ry-768x461.jpg

https://panbo.com/navico-halo24-raym...doppler-radar/

You can rely on distance though.

Irrespective of the accuracy, there is an issue of a new need to be able to add plots to a chartplotter for small commercial vessels in some regions.

I personally use OpenCPN, but will have to stop in 2024 unless I can prove to the inspector that I can plot a fix and submit a location for the plotter to use.

[bcn]

Originally Posted by st599

You can rely on distance though.

Irrespective of the accuracy, there is an issue of a new need to be able to add plots to a chartplotter for small commercial vessels in some regions.

I personally use OpenCPN, but will have to stop in 2024 unless I can prove to the inspector that I can plot a fix and submit a location for the plotter to use.

The Route tool will do - call the result what ever you like. There is bearing and distance one will see on the canvas. Or several "routes" to assign a fix. How do you get bearing and distance? Same as on paper. Compass, Radar, Binocular with compass ...

The Draw plug-in has been cited.
Will this satisfy the officer? Discuss with the UK officials?

[st599]

Originally Posted by bcn

The Route tool will do - call the result what ever you like. There is bearing and distance one will see on the canvas. Or several "routes" to assign a fix. How do you get bearing and distance? Same as on paper. Compass, Radar, Binocular with compass ...

The Draw plug-in has been cited.
Will this satisfy the officer? Discuss with the UK officials?

Unfortunately not. That lets you do the plotting, but you can't then assign that location to the boat for the plotter to start using.

[requiem]

Originally Posted by st599

I personally use OpenCPN, but will have to stop in 2024 unless I can prove to the inspector that I can plot a fix and submit a location for the plotter to use.

This actually sounds like a very favorable environment. In the US there's the option to use an RTCM-compliant ECS in some cases, but that seems to be more a case of "not quite as expensive as ECDIS".

If you merely have to demonstrate functionality rather than be limited to certified / type-approved solutions you have a few options available. OpenCPN (via Draw plugin), SEAiq, and RosePoint should all allow such work.

I personally wouldn't try to use routes for such purposes; it would mean you lose the option of displaying fixes and other marks if you only wanted to display the active route. (Not to mention the importance of labeling one's fixes and clearing lines.)

[bcn]

On the position from the bearings, "Move boat here", or drop a mark. The same you are doing with the pencil on the paper chart.

[bcn]

Originally Posted by requiem

I personally wouldn't try to use routes for such purposes; it would mean you lose the option of displaying fixes and other marks if you only wanted to display the active route. (Not to mention the importance of labeling one's fixes and clearing lines.)

"Route" would be just the already existing tool. To draw references.

[requiem]

Originally Posted by st599

Unfortunately not. That lets you do the plotting, but you can't then assign that location to the boat for the plotter to start using.

Ah, this could be a sticky bit. If the requirement is for a true DR mode, where the plotter then advances own-ship position along the DR plot, you options are much more limited. If you only need to place the own-ship at the position of the last fix, bcn's suggestion is sufficient.

Originally Posted by bcn

"Route" would be just the already existing tool. To draw references.

Agree that it can be used, but since people may have many routes in addition to plotted fixes, that can make a bit of a messy chart. Personally I would find it too confusing to use routes for both.

[merrimac]

Originally Posted by El Pinguino

It would seem that some 4G radars have a thing called 'beam sharpening'.

Supported by radar_pi

[Dockhead]

Originally Posted by merrimac

Ahem, there is a GPS offset that you can enter in the radar_pi plugin? See the attached screenshot of the Advanced > Installation menu. You can thank Douwe who was concerned about this as well and so added it to the plugin...

My Simrad NSX also does this, by the way.

Is that for offset between radar and gps antennae? If so, that's amazing.

[merrimac]

Originally Posted by Dockhead

Is that for offset between radar and gps antennae? If so, that's amazing.

Yup, that is what it is.

[Dockhead]

Originally Posted by El Pinguino

I'm afraid anyone with a typical 'consumer grade' radar who thinks their radar will give them sub one degree bearing accuracy is kidding themselves.

This is from Furuno

'Azimuth Resolution

Suppose that two separate objects are in the same direction, at the same distance, from the boat from which you are looking. The resolution of a radar depends mainly on the horizontal beam width, so the narrower the beam width of an antenna, the higher the resolution of the radar. To increase the resolution of a Radar, we need to reduce the horizontal beam width, which can be accomplished with a larger antenna. There are X-band radars with antennas up to 3 meters wide, and in this case the angular beam width is 0.75 degrees, which is very important for accuracy. On the other hand, Radomes, with an antenna width of about 40cm, have an average horizontal beam width of 5.7°.

https://www.furuno.com/en/technology/radar/basic/



Combine this with the nature of most things you may choose to take a bearing from - with the exception of beacons - and radar bearings are a sub par way of fixing your position.

This is from Panbo- a Navico Halo 24 display.



https://panbo.com/wp-content/uploads...ry-768x461.jpg



https://panbo.com/navico-halo24-raym...doppler-radar/

You can do a lot better bearing than the beam width. Just take the center of the landmark's radar image.

Whether it can be got to sub 1° or not I don't know, but you can do a decent bearing. Good HBC is probably better.

[stevead]

Personally what I find lacking in all of the ECDIS products I have used is the ability to use the traditional navigational techniques that one would normally use on a paper chart.

As this thread has touched on, it would be nice to be able to be able to draw a bearing to landmarks or other objects and derive a cocked hat from which we can plot our estimated position. Similarly it would be nice to draw and calculate a set and drift vector or plot a course making allowance for set & drift.

Unfortunately the OCPN measure tool, and Route manager don't meet these requirements. The OCPN Draw plugin comes close although it is a tad confusing/complicated with its concept of boundary areas. It's almost like we need a "dumbed down" version of the OCPN Draw plugin.

[requiem]

Originally Posted by stevead

Personally what I find lacking in all of the ECDIS products I have used is the ability to use the traditional navigational techniques that one would normally use on a paper chart.

Are you sure you've used ECDIS and not just the consumer stuff? Such features are not optional:

11.4.12.2 It should be possible to display an adequate number of: points, free movable electronic bearing lines, variable and fixed range markers and other symbols required for navigation purposes and specified in appendix 3.

...

11.4.15.1 ECDIS should provide the capability to enter and plot manually obtained bearing and distance lines of position (LOP), and calculate the resulting position of own ship. It should be possible to use the resulting position as an origin for dead-reckoning.

(source: https://imorules.com/GUID-98613BD4-1...02BFED106.html)

[stevead]

Mea culpa,

I was referring to the chartplotting solutions used by recreational sailors.