Facebook

Login

Support Sailonline

If you haven't already - join the SAILONLINE YACHT CLUB!

Please also consider making a donation - all amounts are greatly appreciated!

Board » Technical Support » #4 simple question to Phillipe/maitai.

Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-05-13 10:49:09 - #4 simple question to Phillipe/maitai.
Viva all.

And the questions are:

1 - Does qT uses Time Steps (TS) (in time units) calculations for the Isochrones calculations?
2 - If yes, is it 1 minute the minimum TS?
3 - If it doesn’t use TS for Isochrones calcs, does qT use Distance Step (DS) (in distance units)?
4 - In that case is 1 nm the minimum DS?

Thank you.
Sail Fair.
Posted by
maitai


Users avatar

Posts
114
Registered at
2016-02-25 08:15:33
2016-05-17 07:01:06 - Re: #4 simple question to Phillipe/maitai.
qtVlm uses a time step (otherwise it won't be called isochrone, would it?). The internal time step is configurable in the general settings. The minimum is 1mn. Routing module uses this internal step to calculate a way from one isochrone to the next, but the minimum time step between two isochrone is 5mn. That is already too small and useless, taking too much cpu, memory and time for nothing at all. 30mn or 1h between iso is a much better choice.
Posted by
JB


Users avatar

Posts
305
Registered at
2013-03-07 08:54:34
2016-05-17 13:30:52 - Re: #4 simple question to Phillipe/maitai.
Viva Philippe.

Thank you for your reply but it didn’t clear out my doubts. By the contrary.

I knew/know that qT used/uses one of the two processes: “Time” or “Distance” Step for calculating consecutive Isochrones.
Hence my questions on previous points 1 and 3.

As you know, if the process is a “Time Step” one, we have to use “Time” units for it, (seconds, minutes, hours, etc.).
But, if the process is a “Distance Step” one, the units are “Length” (meter, km, nautical miles, etc.).

In your reply you mix the “internal time step” (sic, I assume that it is in “Time” units) with a “minimum” of “1 nm” for the calculations (I assume it is in “Length” units), and “5 nm” for the distances between consecutive Isochrones (idem).

At minimum, it’s not physically congruent, Philippe.
Or you use time or you use distance. Not both at the same time.

Meanwhile I’ve made a small test with qT - pls see attached picture.
In top of a trivial routing I’ve put two marks, the first at the distance made by the boat on 1 minute and a second mark at a distance made in 5 minutes, this one on top of the first shown Isochrone in the routing.
Well, being an Isochrone calculation what you get in the chart plotter is a representation of the consecutive curves that can be reached at at the same time by a boat travelling at a constant speed between them.
But, again, I’m using here only “time” units (minutes), not “nm” (nautical miles), Philippe.

In relation to your opinion that “is already too small and useless”, the 5 minutes, I totally disagree.
There are several reasons for it. I give you two:

- Light winds;
- Fast boats on tight spaces.

Thank you again, Philippe.
Sail Fair.
Attachments
Posted by
maitai


Users avatar

Posts
114
Registered at
2016-02-25 08:15:33
2016-05-17 13:53:33 - Re: #4 simple question to Phillipe/maitai.
The minimum time between 2 routes points in 1 minute. The minimum time between 2 isochrones is 5 minutes. In case these 2 values are set to the minimum, it means it takes 5 steps to qtVlm to generate one isochrone. There is no distance concept there or elsewhere.
Posted by
maitai


Users avatar

Posts
114
Registered at
2016-02-25 08:15:33
2016-05-18 07:19:22 - Re: #4 simple question to Phillipe/maitai.
Plus: the boat does not travel at constant speed between 2 isos, not in real life nor in qtVlm. Wind and currents change constantly between 2 isos, and qtVlm takes that into consideration.

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

New Ice Age 2026 - Longyearbyen to Browerville


Although we have by no means exhausted the possibilities of ice boating on lakes at high latitudes or high altitudes, it was noticeable that as our 2025 Series progressed, there were calls from time to time for longer-distance challenges, and so in response to these calls we will pretend that global warming has reversed and as a result the coastal waters of Antarctica and Russia and Canada have fully (and smoothly!) frozen over offering us the possibility of a 4-race New Ice Age series in our trusted no-PL DN machines. Our first leg takes us 2600nm from Svalbard’s Longyearbyen east to North Alaska’s Browerville. You’ll be a few days on the ice, so dress warmly and take some provisions; go!
Race #1968
INFOby brainaid.de
DN PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: NIA - SYC
Race starts: Jan 22nd 07:00 Registration Open!
▶ Flash
GO TO RACE

Cross the Convergence 2026 - Robinson Crusoe to Galapagos


Welcome to our first race of a new series of ocean voyages across the World’s convergence zones, this first race taking you north from south of the Tropic of Capricorn to the Equator-straddling Galapagos, home of magical iguanas and other exotic fauna (but no mythical kings, Dory) Departing from the island where in 1704 adventurer Alexander Selkirk inspired Daniel Defoe to write the best-seller "The Life and Adventures of Robinson Crusoe", by debarking off the unsound "HMS Cinque Ports", four months before she foundered off the coast of present-day Colombia, we will sail the 2200nm in our decidedly sounder and faster than the " Cinque Ports",
Ocean 50 !
Race #1983
INFOby brainaid.de
Ocean 50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: CCZ - SYC
Race starts: Jan 16th 18:00 Registration Open!
▶ Flash
GO TO RACE

Bight of Bonny TIMED Race 2026

Welcome to the first TIMED race of 2026! Our race finds us in the Gulf of Guinea and the Bight of Bonny. Starting in Douala, Cameroon the 170 nm course takes us around the island of Bioko with its Caldera and tropical rainforests finishing in Calabar, Nigeria. The boat for this race is the sporty Farr 30. This is a TIMEDrace so you may RE-REGISTER HEREto try again after finishing a run. You will have 13 days and 11 hours to test your skill and decision making after the race opens.
Race #2004
INFOby brainaid.de
Farr 38 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ1 - TRCH - SYC
RACE CLOSE: Saturday,
24 January at 23:00 UTC
Race starts: Jan 11th 12:00 Registration Open!
▶ Flash
GO TO RACE

Cape Town to Rio 2026

Welcome to South Africa and RCYC's classic transatlantic Cape2Rio Race from Cape Town, South Africa, to Rio de Janeiro, Brazil. First run in 1971, this run is buddied with the IRL, Cape2Rio 2025 arranged by the Royal Cape Yacht Club with the cooperation of the
Iate Clube do Rio de Janeiro Despite this being announced the 2025 race (starting dec. 27) it is the 2026 SOL championship kickoff. This virtual version, will be raced once again in Mark Mills' 74ft speedster, the stunning C2R74.
Race #1996 INFO
by brainaid.de
C2R74 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
OCQ1 - OCCH - SUPBUD - SYC
Race starts: Dec 27th 12:00 Registration Closed

▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member KaSToR
  2. Sailonline Yacht Club Member WRmirekd
  3. Sailonline Yacht Club Member CriticalHippo
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member bonknhoot
  6. Sailonline Yacht Club Member Sax747
  7. Sailonline Yacht Club Member rumskib
  8. Sailonline Yacht Club Member vida
  9. Sailonline Yacht Club Member Panpyc
  10. Sailonline Yacht Club Member CollegeFund

View full list

Series

Mobile Client

SYC members have the benefit of access to our mobile/lightweight web client!

The mobile client