Tactics Plugin

[tom_BigSpeedy]

Håkan,

I merged your pull request.
I had to rerun cmake, after that it's compiling w/o errors on VC13.

Thanks,

Thomas

[Hakan]

Yes, the same for me. That could be the change from <two-letters.po files> to <locale_with_underscore.po>? (That's, for example, to be able distinguish between PO and BR Portuguese.)

Håkan

[Gilletarom]

Hello Hakan,

Translation done.

But, please :
- what do you undestand by CMG ?
- When you use the word "Overall", what do you undestand ?

Thank by advance.

[rgleason]

CMG is Course made Good. Which as far as I understand it is not the same as COG, it is the additional vector (red) that is required to result in COG after there is Drift. COG is the actual course taken. CMG is where the bow of the boat is pointing the compass direction of the boat CRS (Course). So CMG is CRS. HDG (Heading) so CMG is HDG or CTS Course to Steer.
gps - What does &#39;Course Made Good&#39; in NMEA string mean? - Geographic Information Systems Stack Exchange




Perhaps we should add some more terms here

Terminology | Official OpenCPN Homepage

for
CMG
SMG

===
Correction, I see that CRS seems to include the effect of "leeway" but not "current", so I was wrong.
So CMG is the same as HDG (Heading)

http://www.starpath.com/cgi-bin/web_...vigation_Rules

[P_Dub]

Originally Posted by Gilletarom

Hello Hakan,

Translation done.

But, please :
- what do you undestand by CMG ?
- When you use the word "Overall", what do you undestand ?

Thank by advance.

Route Fond!

[rgleason]

Now I see there is a difference between "Course to make good" and "Course Made Good"
very confusing. I am going to have to change some terminology I just edited.

Glossary of Terms | Knowledge and Learning | NovAtel

Novatel has some good definitions we do not show, but here is their's for CMG

Course Made Good (CMG)
The single resultant direction from a given point of departure to a subsequent position; the direction of the net movement from one point to the other. This often varies from the track caused by inaccuracies in steering, currents, cross-winds, etc. This term is often considered to be synonymous with Track Made Good, however, Course Made Good is the more correct term.

So perhaps CMG is synonymous with COG? Not quite according to Noval's definition.

Course Over Ground (COG)
The actual path of a vessel with respect to the Earth (a misnomer in that courses are directions steered or intended to be steered through the water with respect to a reference meridian); this will not be a straight line if the vessel's heading yaws back and forth across the course.

Starpath clarifies this

Note we distinguish course over ground from course made good, as one being present dynamic value, and the other being past. The phrase "course made good," can be used to refer to a single track line or to the combination of several course changes between two points. If i sailed 1 mile north and 1 mile east, i made good a course of 045. Or, if i tried to sail course 200 but was being set between 10 and 20°, then i might end up "making good a course" of say 214.

The distinctions between terms is not often critical, but may help to clarify some communications.

[rgleason]

Corrected/Improved in Terminology

[tom_BigSpeedy]

Hi guys,

just check the tactics_pi manual ...
There's a chapter with terminology and also 2 grahics ...
CMG = VMC = course made good. This is the speed you make towards a mark/waypoint


CRS = Course through water



CRS = HDT + Leeway, but without current.

Thomas

[fgd3]

So it appears COG is the direction of the boat's actual movement relative to the surface of the earth while CMG is a summary of COG over time. Does that sound right?

Fabbian

[rgleason]

Yes fabbian. Tactics user manual has great illustrations. Thanks Tom, just did not know quite where I put the pdf.

[tom_BigSpeedy]

Originally Posted by fgd3

So it appears COG is the direction of the boat's actual movement relative to the surface of the earth while CMG is a summary of COG over time. Does that sound right?

Fabbian

Fabbian,

CMG is the component of COG towards a waypoint, like shown in the drawing



Is this clearer now ?

Best,

Thomas

[rgleason]

So where does Course made good (CMG/VMG) fit in this vector diagram?
CMG/VMG requires a WPT, and is as Tom says the component of COG/SOG towards the WPT.

Also CMG/VMG upwind/downwind would be the component of COG/SOG going directly upwind true (TWD) or downwind. This is a far more intelligent measure for optimizing boatspeed in a sailboat than CMG/VMG to a Waypoint!

[tom_BigSpeedy]

Rick,

CMG does not fit into this diagram at all. This diagram only shows how the surface current calculation is done :

Starting from the top vector HDT/STW :
--> you're sailing true heading (bow points to HDT) with a certain speed through water
BUT :
--> due to heel and wind, your boat drifts leewards, the result is CRS / STW.

That means CRS is HDT + Leeway (drift angle)

And finally there is "set" by the surface current, and the result is COG/SOG

If there would be no current at all, then CRS = COG.

This is nothing I invented, this has been used by sailors long before GPS was avaliable to estimate your COG/SOG while you only have HDT and STW to plot the course on paper charts ...:

Simply apply to HDT your boat drift to get CRS (for the german speaking guys, this is known as KdW = "Kurs durch's Wasser", key word "Beschickung Wind" and then add the current vector from the tide tables ("Beschickung Strom")...

The only difference is, that we already have COG thanks GPS, and calculate the current backwards ...


VMG versus CMG :

It is the same formula, but instead of using the bearing to a waypoint for CMG, the VMG uses the (bearing to the) true wind direction ...

CMG makes sense, if you sail crosswind legs towards a waypoint ( with TWA ~90° from any side), because VMG points to 0 then, whereas CMG shows valuable data.


Thomas

[rgleason]

Yes, CMG requires a waypoint. Your excellent diagram could additionally show a WPT and CMG

As I understand it there are several types of VMG one is to a Waypoint and the other is VMG to the wind.

The Dashboard terminology does not currently acknowledge anything but VMG (to a waypoint). I want to make this distinction clear and with unified terminology in OpenCPN and across all plugins.

The VMG to waypoint is much less useful for determining optimal sailing than VMG to upwind/downwind.

[fgd3]

Originally Posted by tom_BigSpeedy

Fabbian,

CMG is the component of COG towards a waypoint, like shown in the drawing

Attachment 128298

Is this clearer now ?

Best,

Thomas

Not a bit. The component of COG towards a waypoint (your definition of CMG) seems like a useless measure. It's just the bearing to the waypoint at the start of the leg. Velocity Made Good (VMG) is useful in telling you if you are going to reach an upwind destination sooner by sailing as close to the wind as possible or falling off a bit to get an increase in speed. It also applies to a downwind destination, telling you if it's better to sail dead downwind or to tack downwind. But what does CMG as you've defined it tell you? The component of COG towards a waypoint is always the same no matter what course you steer.

On the other hand, all the earlier discussion in this thread defined CMG as the vector sum of the COG of various legs. That's at least somewhat useful, as it allows you to compare the bearing to an upwind waypoint with your actual progress towards the waypoint. If CMG is different from bearing to the waypoint you can adjust the length of your tacks to optimize your progress to the waypoint.

It's not real important to me, but I think you all need to make up your minds and be clear about it.

Fabbian