Time to Target

[Aldebaran17]

Time to target in the Route console seems to be calculated wrong.

Please have a look at this screen shot:



The angle between the target (bearing 355) and heading (315) is 40 degrees. This results in a VMG of 4.4 knots * cos(40) = 3.37kn, based on SOG. Close enough to the displayed value.

At a range of 7.24 nm this should correspond to a TTG@VMG of more than 2 hours (~ 2h 08min). The displayed TTG (1h38m) is based on SOG (7.23nm / 4.4kn = 1.65h = 1h38min).

BTW: the difference between SOG and STW is real due to tidal stream pretty much on the nose

And: it is OpenCPN 5.6.2 running on a PI. Did not manage to install 5.8. on Openplotter yet.

Manfred

[Aldebaran17]

Since nobody was responding to my post, I had to do some research myself.

After looking in the code, I figured that TTG is based on VMG if the Active Route window is set to "This leg" and it is based on SOG when looking at the entire "route".

You could argue if it is better to calculate the TTG for the entire route based on VMG or SOG. Both will be substantially wrong in cases.

However, a few things can be improved:

1. documentation: the difference between SOG or VMG used for TTG is not explained in the manual.

2. The text used in the active route console window says "ETA @ VMG" and "TTG @ VMG", but should say "ETA @SOG" and "TTG @SOG"

3. When the console is set to "Route" and it the last leg of a route is the active one, then TTG should be calculated based on VMG.

4. The screen shots used in the manual are outdated (do not show the issue above) and the nomenclature used is not consistent. E.g. in the text it says "Current Leg", whereas in the software "This leg" is used.

5. Finally speaking of nomenclature: in the manual the window is called active route console window, kind of long, but I see what it refers to. In the options window, when setting the font sizes it is referred to as console, not very specific in my opinion. It took me ages to find these options controlling the fonts of the console a while ago. However, for me the canonical console is a mixing console with dozens of knobs and sliders and blinking lights. Probably my picture is old-school, but I guess you get the idea. The active route console window, which just displays numbers, no user controls, does not look like a console to me. This may be due to the fact, that I am not a native speaker. Then, just ignore what I said.

Best,

Manfred