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Old 19-10-2020, 03:41   #1
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Weatherfax georeferencing

Hello and thanks in advance,
I am trying to exploit WetherFax plugin capabilities to georeference forecast maps or surface analysis maps or satellite photos, possibly overlading them.
In order to georeference the images I need the geographic coordinates so that any pixel position on the map determines the true geographic position.
However, when I download a synoptic chart from DWD Wetterzentrale or UK Met Office for example, the geographic coordinates are lacking. So my question is: How can I find the geographic coordinates of a downloaded image? I noticed from David Burch book Modern Marine Weather that charts downloaded from OPC have these informations but for some reason that still I have to fix, these are the only maps that I cannot download with WeatherFax. Is there the possibility to download an already georeferenced synoptic chart or satellite image? Provided that it is possible, do I have to convert the file in a .kap format to be imported in OpenCPN? What is the file format of the georeferenced map in WeatherFax plugin?
Very grateful for your answer

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Old 19-10-2020, 04:12   #2
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Re: Weatherfax georeferencing

Please read the documentation, https://opencpn.org/wiki/dokuwiki/do...her:weatherfax , including links to more resources. Come back after that, if necessary.

Thomas
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Old 20-10-2020, 15:01   #3
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Re: Weatherfax georeferencing

Quote:
...To georeference the images I need the geographic coordinates so that any pixel position on the map determines the true geographic position.
However, when I download a synoptic chart from DWD Wetterzentrale or UK Met Office for example, the geographic coordinates are lacking.
Yes, you are correct, the georeferences have to be shown on the image in order to use the Overlay Wizard, successfully. Often times these references are not completely clear, or you have to use a coordinate line that is not optimal. Sometimes you have to just try it, determine how it overlays and then just try again. However I would bother using images that do not have the coordinates shown, and clearer the coordinates are, the easier it is to get it right the first time.


This is the first time I have heard that DWD Wetterzentrale or UK Met Office do not have the georeferences!!
You had best go after them to get those back, and I hope everyone will pester and persist until they show clear georeferences. That is a disservice to all.


In answer to you last question. Is there a place to download met maps that are automatically georeferenced?
Yes, weatherfax should generally be updated at least every 3 months and this should be maintained by the users, but is not.
David, Hwe and I updated weatherfax not that long ago, but the weather services keep changing.


Perhaps a group of clever users should get together and update all of the weatherfax urls, or at least the ones in their section of the world, and then send the changes via the Cruiser Forum designated Weatherfax thread (not this one!)


Also reading that thread will give you more insight.
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Old 20-10-2020, 15:18   #4
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Re: Weatherfax georeferencing

BTW I just used Weatherfax v1.9.14.0 and it appears to me that all the NOAA weatherfaxes overlay properly when selected and a number of the German and UK wxfaxes work, so my conclusion is you are not using this tool properly and should RTFM (Read the Manual) before implying it does not work.
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Old 21-10-2020, 08:18   #5
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Re: Weatherfax georeferencing

There is clearly a misunderstanding probably due to language problems and I want to excuse me. My simple question is: I have 3 pictures like the following.
Fig 1 shows geographic coordinates easily recognisable
Fig 2 they are present but difficult to identify when zooming
Fig 3 coordinates are not seen (OpenCPN can convert polar image into Mercator).
So, how to handle in order to georeference the images?
Thank you and sorry again for the triviality of the question
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Old 21-10-2020, 13:42   #6
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Re: Weatherfax georeferencing

fabiobeltra...

Retrieve...Internet
Select provider and region.
Select forecast you need.(X)
Highlight and use the 'Selected' button.

Let us know if this works for you.

Mike
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Old 21-10-2020, 15:29   #7
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Re: Weatherfax georeferencing

Thank you

Fig 1 - I pick the two cross corners where I am going to pick, ahead of time and write down the lat/long coords for use later when selecting in the wizard.
Fig 2 - Yes it is difficult, do the same as above, try to remember the positions you decided on for the best overlay. If you made one of the corners wrong, just edit it again until you get it the way you want it.
Fig 3 - GOES images are more difficult. Try to pick peninsulas and points on continent outlines, in this image 1. The tip of Florida 2. The point on the Soviet Union. Then from Opencpn charts write down those lat/long coordinates and use those locations in the wizard.
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Old 21-10-2020, 15:30   #8
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Re: Weatherfax georeferencing

Quote:
Originally Posted by Rasbats View Post
fabiobeltra...

Retrieve...Internet
Select provider and region.
Select forecast you need.(X)
Highlight and use the 'Selected' button.

Let us know if this works for you.

Mike

Thanks Mike, that's definitely worth adding to the wiki.
Which I will do.


https://opencpn.org/wiki/dokuwiki/do...rieval_summary


The points are doubled to make the point in different ways!
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Old 22-10-2020, 10:42   #9
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Thanks to everybody. From your answers I am finally confident that I was in the right way. Moreover, NOA pictures could not be downloaded because of antivirus. Great
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