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

Posted by
JB


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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


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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


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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.
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Posted by
maitai


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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


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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.

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