Discussion utilisateur:Rgleason

With Maitai's instruction, I've tried to write some more detailed description. I will try to upload illustrations later and work on the formatting, structure, language and details in this further.

Download a Grib File first - Grib Files and Use

Download Grib

1. Select an area with the cursor by picking opposite corners.

2. Pick "Gribfile > Download" or Download from VLM (easiest way). Follow prompts.

3. Pick "Gribfile > Open" and pick the most current grib file.

4. A grib file must be downloaded before a Routing can be done.

Grib Update Schedule and accuracy

VLM 5 days 04h20, 10h20, 16h20, 22h20 UTC; Intrm-35mn before(12h).....[23h20, 5h20, 11h20, 17h20 EST]

Zygrib 8 days 05h05, 11h05, 17h05, 23h05 UTC..........................................[0h05, 7h05, 12h05, 18h05 EST]

UGrib 7 days 05h25, 11h25, 17h25, 23h25 UTC..........................................[0h25, 6h25, 12h25, 18h25 EST]

Saildocs Up to 16 days, large files, File from NOAA, Email

Accuracy and Route Information

VLM Files take the form "gfs_NOAA-2012121506.grb". The four daily VLM gribs begin with gfs_NOAA-[date] and end in "00", 06", "12", "18". The VLM 5 day grib file is used by the server to calculate all positions, for all virtual races and is the best one to use for preparation of 5 day, shorter more accurate "Routings" and "Routes" for the boat to follow during the race. For longer course planning the Saildocs grib recieved via email is useful. The Saildocs grib files differ slightly from VLM grib for the first 5 days, but offer up to 16 days and are good for approximation of longer routes which will change. Keep in mind that your boat's autopilot must be following a "Route" for as long as your next update interval, otherwise it will not progress and go off course. It is best to download a fresh grib shortly after it has become available. After selecting "GribFile/Download from VLM", you should "GribFile/Open" the file.

Also, each time there is an update of grib in the VLM Server (see schedule above) your route is not precise anymore. Since this it occurs every 6 hours there is a big chance you were sleeping at one point. When a new grib has been issued, it is very possible that your boat will no longer be following the optimized route. During this time, depending on the nature of the weather, the difference between the optimized route and the course your boat's autopilot is following may be larger or small (experience helps). In practice, if you know you will miss a [grib] meteo update (during sleep for example), prepare the route a bit differently, and don't sail too close to the rocks, or leave an adequately safe distance from the gates.

If you don't miss a meteo update and download a fresh grib each time, then the route is 100% accurate (maybe not the best, but what it shows is what the boat will do). Using qtVlm together with VLM you get exactly the same grib, interpolation algo for winds and polars, etc. Which is quite normal since it's made by the same team, and VLM/qtVLM are openSource anyway.

Once the skills for downloading gribs, using them appropriately, creating "Routings", converting to "Routes" and "Sending" to the Autopilot are mastered, you will have the challenge of predicting how the new grib file predictions will change between updates, in order to gain positions in the virtual race.

Make a POI to head towards - Marks/POI

Create a POI Locate cursor, right click and select "Place a new Mark". A POI is Point of Interest.

Edit a POI right click on it and pick "Edit mark".

Drag a POI or Mark Push shift down and left mouse button while highlighting the POI. Then drag the POI and release the mouse button. Then release the shift key.

Delete multiple POI select a rectangular area with the cursor and mouse, right click and pick "Delete".

Barriers are created using two POI or Beacons to prevent the "Routing" algorythm from considering certain areas. Locate the two POI or Beacons, then right click and Pick "Draw/edit a line to another POI" At the present time, POI/Beacons can only accept one line (in pairs of POI).

It is a good idea to keep your POI list simple by deleting ones that are not needed to avoid confusion with selection of POI with the same name.

Difference between a "Routing" and a "Route":

The two primary tools for optimizing routes are "Routing" and "Routes". Normally, after download of a current Grib file, you "Routing > Create a Routing" from your boat to a "Mark" or "POI" that you have created previously. Then from the "Routing > Edit" Route Settings dialogue box you can check "Convert to a Route" to do more "Simplification" and "Optimization".

Routing When learning, start first with a "Routing" which will calculate the best path from arrival to start based on your polar and the grib, using isochrons method. Avoid certain areas by putting "Barriers" on the map (see POI), but this is normally not needed. To create alternative child routes using "Right click - Create a Pivot" see notes below.

Convert to a Route Then to "Simplify" and "Optimize" a path to a POI, the "Routing" must be converted to a "Route" by checking "Convert to a Route" in the "Edit Routing" Route Setting dialogue box.

Route Simplification: (Check in Edit Route dialogue box) Routings have one Intermediate POI at each isochrone crossing which requires "Simplification" in order to Send a short list of 6 POI to the Autopilot and not overburden the server. The Simplification process will remove all POIs that do not improve the ETA, (typically aligned POIs are often not needed).

Optimization: (Check in Edit Route dialogue Box)

Then eventually you can "Optimize" the "Route". Basically this process will try to reposition the POIs in better locations, because the routing process only looks at fix step (one hour), so it is understandable that a point might be better placed in between 2 isochrones. This is perfectionism, and IRL (in real life - actually sailing) not really useful, because the grib is not precise enough, however it is very useful in Virtual Racing (VLM), because the grib is of course 100% accurate in that case.

Next Create a "Routing" - Use of "Routing > Create": -

1. Routing > Create a Routing Start by Creating a Routing from the your boat to a particular POI that you have placed on the current grib. to create a POI, put the cursor at a destination location, use right mouse button and select "Place new mark". Then pick Routing > Create new Routing. Change the destination using the dropdown box to pick the new POI you created. Select "Apply" and let the isochrones and Routing be created. If you check "Convert to a Route" while creating the "Routing" the conversion will occur automatically with a prompt to "Simplify and Optimize" or to "Cancel conversion to a Route". When learning "Routing > Create a Routing" I suggest that you don't check "Convert to a Route" for awhile.

2. Routing Explanation "Routing" is different than a "Route". A "Routing" optimizes ETA using predicted wind from a Grib file, from the boat (or Mark) to a selected POI-Mark. Routings show "isochrones" which indicate lines of identical sailing time or ETA. These are similar to isobars (which show lines of the same pressure) but for sailing time or ETA. You will see "isochrones" that are close together, this means that sailing there is very slow (often caused by no or little wind). Conversely, if the isochrone lines are far apart then you are sailing faster in heavier winds. A "Routing" creates a good route optimization and shows the isochrones from the boat or the starting location. It is very important to select good destination points, by thinking about what the winds and weather is likely to do during the plotting and afterwards. It is helpful to study multiple "Routing"s. Once you have a "Routing" you like, it is time to convert it into a "Route". See "Convert to routing" below. 3. Route Details "Routing" does not show lat/longs, courses, boat speed, & winds along the "Routing", this is another reason to convert your "Routing" into a "Route". Then "Route > Edit" and see the route's "Details" tab, or "Route > Edit" and check "Display data from roadbook at grib date" option, to see all this while you change the grib's date.

Convert "Routing" to "Route":

1. Routing > Edit > Convert a Routing to a Route Use the Edit Routing Dialogue box and Check the "Convert to Route" box. Hit "Apply" the program will prompt "Is route from Boat?" If you select "No", the "Route" can then be "Frozen" (see below). If you select "Yes" the route will start be from the boat and will follow the boat around as it moves with each grib update, and you will continue to be able to "Optimize" and "Simplify" that "Route".

Simplify and Optimize the "Route" - Use of "Routes > Edit":

1. Route > Edit Name, size and color, start point, start date and time (good for sequential routes), Options, etc. see below

2. Route > Edit > Optimize a Route Check the box in the Route Dialogue and watch the program cycle through an optimization.

3. Route > Edit > Simplify a Route Check the box in the Route Dialogue after you have optimized the route, to simplify and reduce the number of Intermediate POI's used. Why is this necessary? Because at some point you will be sending the list of waypoints to the "Autopilot" and the Autopilot only accepts six or seven intermediate waypoint instructions. Also it is often better to let the optimization between intermediate POI or waypoints occur in accord with how the actual winds blow. Fewer waypoints allow this to happen.

4. Route from your Boat to POI can be re-run multiple times, and "Simplified", "Optimized" with newly download and up-to-date grib files. This is a shortcut if you are keeping the destination point the same. Sometimes the weather has changed enough that it is wise to review weather and set a new destination POI and create a new Routing and then convert that to a Route. But re-running an existing Route is good way to save time.

5. Route from POI to POI can be Frozen and unfrozen, but cannot be used on a fresh or new grib file to update the optimization of a route.

6. Route > Edit > Option to Freeze a Route- The Route must start from a POI (and end at a POI) and not be on VB-VLM. Routes from point to point can be frozen. Freezing the route stores all time and waypoint information for the last optimization. As you cycle through time the position will be shown, but it is for a previous (not current) grib file. If you uncheck a frozen route, and try to optimize it, it will complain and the route will probably disappear. Don't do this. You can hide and unhide frozen routes or export them.

7. Route > Edit > Option to Hide and Unhide a Route - Useful to identify a Route (you can also use hover) or to clean up the screen. Often I find myself eventually deleting hidden routes. It would be helpful to have the delete route option show if a route is (hidden).

8. Route > Edit > Option to Export/Import a Route - Simply save a route to a file (csv, txt, etc) Asks for POI or Detail. Or Import or retrieve an older route.

9. Route > Edit > Option to display wind's strength along the routing -edit routing, uncheck "see Isochrons", and check "Color TWS between isos" instead.

10. Route Details -"Routing" does not show lat/longs, courses, boat speed, & winds along the "Routing", Then "Route > Edit" and see the route's "Details" tab, or "Route > Edit" and check "Display data from roadbook at grib date" option, to see all this while you change the grib's date.