February 9, 2018 at 12:38 am #300
[From User Stephane]
In the manual, it is mentionned : “Time Resolution” is specified in decimal hours, and determines how finely a forecast wind period is interpolated. For example, if the wind forecast period is 12 hours, and the time resolution is 2, then wind values will be interpolated every two hours within the period. Within each two hour window, the wind will be assumed constant. ”
I have one GRIB file with data each 3 hours. So I put Time Resolution (h) : 3.0 and then I run a optimization.
But in the nav details, it seems that the wind is not assumed constant within each 3 hours window as I can see in the column “Wind”.
Do you know why ?
Thanks and thanks for this nice tool.
February 9, 2018 at 12:38 am #301
Glad you find the tool useful.
The wind is always recalculated (through interpolation) at routepoints, whether they are user-created marks or generated by the optimizer. There is no way to disable this. The time resolution parameter applies when the vessel is traveling along long legs between routepoints.
I’m curious – would you prefer not to have interpolation happen at routepoints? I can understand that.
February 9, 2018 at 12:39 am #302
Thanks for your answer.
I am a particular user because I don’t sail.
I want to use your tool with students.
The GRIB files I have are 0.5 ° by 0.5 °, a geographical interpolation is preferable, but for ease of understanding, I would have liked no temporal interpolation between the three hours data that I have in a GRIB files.
What kind of geographically interpolation do you use ? Linear or spline ?
If I understand correctly, between two routepoints, there is no temporal interpolation (and geographically ?) and the wind is recalculated for each routepoint with a interpolation between the time and time+3 hours. Is that correct ?
Thank you, I’ll try to think about how to use it knowing these facts.
February 9, 2018 at 12:39 am #303
Interpolation is linear along the three dimensions of lon, lat, and time. The wind is calculated by interpolation for lon/line/time at each routepoint, and along the leg between routepoints every t hours, where t is the time resolution.
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