Integration with QtVlm - Data files and Import/Export

[rgleason]

Perhaps if it is in a description you say "Tidal Current from tidal grib" otherwise I think I'd stick to Current

[rgleason]

Yes as I understand it, COG and SOG, include the effect of the Current (capitalized I guess is important!) the "Data at the Roadway" - descriptive term by the way, so the HDG and BS are calculated from the boats polars (but are normally from the boat compass and speedo)

[rgleason]

Dear Phillipe (Maitai) and Oxygen77, & Jesper?

I am afraid this is pretty long and I may not be posting correctly, I apologize for that. First I'd like to say that I think qtVlm is a quite remarkable piece of software, and I keep finding parts of it that are more powerful and useful. (Same thing goes for Opencpn!) I have not tried it in the Loup but will, I am learning it first. I guess I should have known some of this that follows:

Data at interpolation point for Route (at Boat Location)
Shows grib data and planning information for the Boat at a selected time and location.

Wind Current Data
TWD True Wind Direction (Compass, relative to North)
TWS True Wind Speed (Wind speed relative to a stationary point)
TWA True Wind Angle (Angle from Boat centerline)
AWS Apparent Wind Speed (Wind speed relative to the Boat)
AWA Apparent Wind Angle (Angle from Boat centerline)

Boat and WP Data
HDG Boat Heading (Compass, relative to North) (determined by Polar Diagram & Grib wind)
BS Boat Speed (Speed through the water, speedo) (determined by Polar & Grib wiind)
COG Course over Ground (Includes efffect of Tide/Current grib, if it exists)
SOG Speed over Ground (Includes effect of Tide/Current grib, if it exists)
CD Current Direction (NA if no Tide/Current grib is loaded)
CS Current Speed (NA if no Tide/Current grib is loaded)
CNM Course to Next Mark (i.e. orthodromic heading to next POI)
DNM Distance to Next Mark (i.e. orthodromic distance to next POI)

If I have anything wrong, please correct me, I probably should have known several of these instantly, but the thing I have to remember is the Data Window is not showing Nmea data from instruments, its using the prediction or grib information to show what it calculates for that position .

Perhaps you are planning this, butt it would be very nice if the "Data at interpolation point for Route" and boat positon would change when you click or double click on the route. Also ability to click Mark / Delete / <select>

I was looking at the Wiki and wondered how you can see or get to "pilototo". Is this something that appears when in loup du mer mode?
This looks like it might be an early verrsion of Route and Route Details?

I would like to try to progam an idea because I think it might simplify and distill the information available through Nmea and all the instruments.

I will try to draw it, and explain it. I've been working on the geometry formulas and trying to determine if it could be done with Excel, but it might be better and more useful if it could be integrated into both QtVlm and OpenCpn as a window. In the case of QtVlm I think it might be best if it could work with anticipated or predicted Grib information or a real Nmea data stream (user selection).

I am sure there are problems I have not even thought about yet, but I did do programming in Pascal for a CAD program, making fairly good and useful macros for we Architects at a time when the software was very young.

I will try to describe it and perhaps you can advise if you think it is possible to use qtVlm to program this? Your Route / Detail Route Tab has an icon with the beginning concept, or at least some elements of it...
1. Boat shape turned to align with HDG
2. Wind shown as TWD and TWS relative to the boat.

I you would look at the attached spreadsheet, Dynamic-boat-wind-current-vectors.pdf (Was xls but not place to upload that I could find. Hope this link works. Equations are not done yet.) I think you'd understand the graphics

Any help or suggestions would be appreciated.

Best Regards,
Rick

[maitai]

Rick,

A quick answer:

Your explanations for the acronyms used in qtVlm are correct.

The pilototo (autopilot) feature in qtVlm is something used only in VLM mode. Basically you can send up to 5 orders to the VLM server (a date/time + a new heading for instance). This feature is of course useless in real-boat mode. Also note that the dashboard is quite different between the 2 modes.

Concerning the ability to switch the road info from NMEA or GRIB, it's not the aim of a route. A route in qtVLm shows predicted informations, and of course you don't know what NMEA data will be in 2 hours... These information from NMEA data (HDG, COG, SOG, AWA, etc) should be somewhere in the dashboard I think.

I had a quick look at your pdf file and I think it's quite correct. Just to complete a bit:

For calculating AWA and AWS there is an excellent site: True and Apparent Wind Calculator
The formulas given are correct... if there is no Current (note the uppercase ). If there is Current then TWD and TWS must be recalculated before applying the formulas, because the wind on water is not the same as the wind on ground, except if you are anchored. If TWD and TWS are taken from NMEA data then there is no need to recalculate them, but then probably you can take AWA and AWS directly from the NMEA data. The AWA/AWS displayed in qtVlm take the Current into consideration if information is available.

The VMG formulae is cos(abs(CNM-HDG))*BS. Finding the Best VMG (BVMG) consists in varying HDG until VMG reaches a pick.

[rgleason]

Phillipe (Maitai), Thank you for the explanations, and VMG formula, very helpful.
This is a helpful link: True and Apparent Wind Calculator I am going to have to think about the information about the Current and TWD and TWS recalc. You say wind on the water is not the same as wind on the ground. Is that because the wind is affected by the current??? ...No, what you are pointing out is that the Apparent Wind calculator above does not have the Current speed and direction included, which would also be an important factor changing the Apparent Wind because the Current afffects the boat and thus the apparent wind.

My Wind and Boat Diagram did NOT account for the Current component, thank you for the correction and the VMG formula. It is complicated stuff. -Does this get multivariable?

I would like to try to animate these and connect to Nmea and the Predicted Route or Roadway. Is there a program structure that I could use?

[maitai]

Let's imagine you are anchored, no moving, and heading North. Let's say the grib says TWD is 0 and TWS is 20kts. In that case AWA and AWS are the same as TWD and TWS. If there is Currents, then it's the same thing since you are not moving, and what you feel is the wind-on-ground.

Now let's imagine the same situation, but NOT anchored. You are still not moving on the water, but you are moving WITH the water because there is Current. Let's say that Current is South (going from North to South), at 5Kts. Then it's obvious that your AWA is still 0, but that your AWS is now 15kts.

Conclusion is that when you are sailing, you should use TWD-on-water and TWS-on-water to calculate AWA and AWS (and to interpolate BS from polars), and not TWD-on-ground and TWS-on-ground. Anyway what you get from NMEA is "on-water", so no problem. But if you take data from grib, then it's a different story and you should take care of this.

For the rest I don't know, it all depends on the language/architecture you are using. Excel and a VB macro can do all that I guess.

[maitai]

Version 3.3.2 is out. See here http://www.cruisersforum.com/forums/...ml#post1069461 for more details.

[sinbad7]

Paul...

Hope you and your boat is safe in Florida,although perhaps you have some shelter on the river?

Nasty stuff coming!!

Tore

[rgleason]

QtVlm has been very useful for prediction/timing of wind speed & direction. I hope the tidal departures are less than Noaa is predicting! - Westerly, RI

[rgleason]

Maitai wrote:

Let's imagine you are anchored, no moving, and heading North. Let's say the grib says TWD is 0 and TWS is 20kts. In that case AWA and AWS are the same as TWD and TWS. If there is Currents, then it's the same thing since you are not moving, and what you feel is the wind-on-ground.

Now let's imagine the same situation, but NOT anchored. You are still not moving on the water, but you are moving WITH the water because there is Current. Let's say that Current is South (going from North to South), at 5Kts. Then it's obvious that your AWA is still 0, but that your AWS is now 15kts.

Conclusion is that when you are sailing, you should use TWD-on-water and TWS-on-water to calculate AWA and AWS (and to interpolate BS from polars), and not TWD-on-ground and TWS-on-ground. Anyway what you get from NMEA is "on-water", so no problem. But if you take data from grib, then it's a different story and you should take care of this.

This Ockum webpage also discusses the difference between:

TW ground relative -

TW water relative - Polar plots always use TW water relative, TWA's are the same because the boat is symmetrical Port & Starboard relative to the boat in the water (If COG & SOG are used to calculate TWA, then TWA would be different on opposite tacks ) - In other words, TW water relative does not see Current.

Why Paddles (Boat Speed) and Heading sensors are important when GPS provide the information? Refer to Ockum Why Paddles?

Since COG/SOG is relative to land and not water; anything derived from it includes current. If COG/SOG is used to calculate speed and wind angle, tack data will be different on opposite tacks, and changes with whatever current you happen to be in at the moment.

It is becoming clearer that the difference between COG & SOG and Boat HDG and Speed will include the effect of current and leeway, and must be accounted for in calculations.

[rgleason]

Maitai, I notice you've entered this race and it starts on the 10th. Is this a reasonable one to try, as a starter?
http://virtual-loup-de-mer.org/ics.php?idraces=20121110
Race : Le Vent des Globes
This race has not started yet
Start date : 2012/11/10 12:02:00 GMT

[rgleason]

TW ground relative (which includes the effect of current, is best for course planning, and determining VMG and BVMG and the best way to get to a Wpt. COG and SOG are used (most likely through use of GPS)

TW water relative (which does not include the effect of current), is best for fine tuning and sailing a boat through the water most effectively. It does not account for current. Boat Speed (BS) via paddlewheel or transcducer and Boat Heading (HDG) via Fluxgate Compass are most often used.

How does boat leeway fit into this picture? Is does not appear to be accounted for through the polar diagram because the polar plots Boat Heading HDG.

[maitai]

Once you have calculated TWS and TWD water relative, you can calculate TWA water-relative, and then use the polar to find BS. Then knowing BS, HDG, CS and CD you can calculate COG and SOG. And then Route and Routing modules can use COG and SOG to calculate their stuff. The boat leeway is the difference between (COG,SOG) and (HDG,BS). A vector substraction.

[maitai]

Originally Posted by rgleason

Maitai, I notice you've entered this race and it starts on the 10th. Is this a reasonable one to try, as a starter?
http://virtual-loup-de-mer.org/ics.php?idraces=20121110
Race : Le Vent des Globes
This race has not started yet
Start date : 2012/11/10 12:02:00 GMT

Well what can I say.... It's a race that occurs once every 4 years, the best of all. A must. The real event is here, surely you have heard about it Vendée Globe - Vendée Globe 2012-2013

If you intend to participate I strongly advise to train a bit before for instance with this race Virtual Loup-De-Mer, which is using the same boat/polar and that you can start/restart at leasure. You need to learn a bit about VLM's navigation modes and especially autopilot (pilototo as we call it)

Anyway there is no risk in trying... A lot of us do that in "tourist" mode and it's fun too. And you quit whenever you like

[sinbad7]

rgleason..

I have just downloaded the Vendee Globe app on my Galaxy smartphone and look forward to follow the race in 5 days.

Tore